Electron spin resonance detected by a superconducting qubit
Kubo, Y; Grezes, C; Umeda, T; Isoya, J; Sumiya, H; Yamamoto, T; Abe, H; Onoda, S; Ohshima, T; Jacques, V; Dréau, A; Roch, J -F; Auffeves, A; Vion, D; Esteve, D; Bertet, P
2012-01-01
A new method for detecting the magnetic resonance of electronic spins at low temperature is demonstrated. It consists in measuring the signal emitted by the spins with a superconducting qubit that acts as a single-microwave-photon detector, resulting in an enhanced sensitivity. We implement this new type of electron-spin resonance spectroscopy using a hybrid quantum circuit in which a transmon qubit is coupled to a spin ensemble consisting of NV centers in diamond. With this setup we measure the NV center absorption spectrum at 30mK at an excitation level of \\thicksim15\\,\\mu_{B} out of an ensemble of 10^{11} spins.
Controlling electron quantum dot qubits by spin-orbit interactions
Stano, P.
2007-01-15
Single electron confined in a quantum dot is studied. A special emphasis is laid on the spin properties and the influence of spin-orbit interactions on the system. The study is motivated by a perspective exploitation of the spin of the confined electron as a qubit, a basic building block of in a foreseen quantum computer. The electron is described using the single band effective mass approximation, with parameters typical for a lateral electrostatically defined quantum dot in a GaAs/AlGaAs heterostructure. The stemming data for the analysis are obtained by numerical methods of exact diagonalization, however, all important conclusions are explained analytically. The work focuses on three main areas -- electron spectrum, phonon induced relaxation and electrically and magnetically induced Rabi oscillations. It is shown, how spin-orbit interactions influence the energy spectrum, cause finite spin relaxation and allow for all-electrical manipulation of the spin qubit. Among the main results is the discovery of easy passages, where the spin relaxation is unusually slow and the qubit is protected against parasitic electrical fields connected with manipulation by resonant electromagnetic fields. The results provide direct guide for manufacturing quantum dots with much improved properties, suitable for realizing single electron spin qubits. (orig.)
Semiconductor quantum dots for electron spin qubits
van der Wiel, Wilfred Gerard; Stopa, M.; Kodera, T.; Hatano, T.; Tarucha, S.
2006-01-01
We report on our recent progress in applying semiconductor quantum dots for spin-based quantum computation, as proposed by Loss and DiVincenzo (1998 Phys. Rev. A 57 120). For the purpose of single-electron spin resonance, we study different types of single quantum dot devices that are designed for
Tunable Few-Electron Quantum Dots as Spin Qubits
Elzerman, Jeroen; Hanson, Ronald; Greidanus, Jacob; Willems van Beveren, Laurens; de Franceschi, Silvano; Vandersypen, Lieven; Tarucha, Seigo; Kouwenhoven, Leo
2003-03-01
Recently it was proposed to make a quantum bit using the spin of an electron in a quantum dot. We present the first experimental steps towards realizing a system of two coupled qubits. The Zeeman splitting between the two spin states defining the qubit is measured for a one-electron dot in a parallel magnetic field. For a two-electron dot, we control the spin singlet-triplet energy difference with a perpendicular magnetic field, and we induce a transition from singlet to triplet ground state. We find relaxation from triplet to singlet to be extremely slow (> 1 mus), which is promising for quantum computing. We couple two few-electron dots, creating the first fully tunable few-electron double dot. Its charge configuration can be read out with a nearby QPC acting as an integrated charge detector.
Sato, Kazuo; Nakazawa, Shigeki; Rahimi, Robabeh D.; Nishida, Shinsuke; Ise, Tomoaki; Shimoi, Daisuke; Toyota, Kazuo; Morita, Yasushi; Kitagawa, Masahiro; Carl, Parick; Höfner, Peter; Takui, Takeji
2009-06-01
Electrons with the spin quantum number 1/2, as physical qubits, have naturally been anticipated for implementing quantum computing and information processing (QC/QIP). Recently, electron spin-qubit systems in organic molecular frames have emerged as a hybrid spin-qubit system along with a nuclear spin-1/2 qubit. Among promising candidates for QC/QIP from the materials science side, the reasons for why electron spin-qubits such as molecular spin systems, i.e., unpaired electron spins in molecular frames, have potentialities for serving for QC/QIP will be given in the lecture (Chapter), emphasizing what their advantages or disadvantages are entertained and what technical and intrinsic issues should be dealt with for the implementation of molecular-spin quantum computers in terms of currently available spin manipulation technology such as pulse-based electron-nuclear double resonance (pulsed or pulse ENDOR) devoted to QC/QIP. Firstly, a general introduction and introductory remarks to pulsed ENDOR spectroscopy as electron-nuclear spin manipulation technology is given. Super dense coding (SDC) experiments by the use of pulsed ENDOR are also introduced to understand differentiating QC ENDOR from QC NMR based on modern nuclear spin technology. Direct observation of the spinor inherent in an electron spin, detected for the first time, will be shown in connection with the entanglement of an electron-nuclear hybrid system. Novel microwave spin manipulation technology enabling us to deal with genuine electron-electron spin-qubit systems in the molecular frame will be introduced, illustrating, from the synthetic strategy of matter spin-qubits, a key-role of the molecular design of g-tensor/hyperfine-(A-)tensor molecular engineering for QC/QIP. Finally, important technological achievements of recently-emerging CD ELDOR (Coherent-Dual ELectron-electron DOuble Resonance) spin technology enabling us to manipulate electron spin-qubits are described.
Hybrid quantum circuit with a superconducting qubit coupled to an electron spin ensemble
Kubo, Yuimaru; Grezes, Cecile; Vion, Denis; Esteve, Daniel; Bertet, Patrice [Quantronics Group, SPEC (CNRS URA 2464), CEA-Saclay, 91191 Gif-sur-Yvette (France); Diniz, Igor; Auffeves, Alexia [Institut Neel, CNRS, BP 166, 38042 Grenoble (France); Isoya, Jun-ichi [Research Center for Knowledge Communities, University of Tsukuba, 305-8550 Tsukuba (Japan); Jacques, Vincent; Dreau, Anais; Roch, Jean-Francois [LPQM (CNRS, UMR 8537), Ecole Normale Superieure de Cachan, 94235 Cachan (France)
2013-07-01
We report the experimental realization of a hybrid quantum circuit combining a superconducting qubit and an ensemble of electronic spins. The qubit, of the transmon type, is coherently coupled to the spin ensemble consisting of nitrogen-vacancy (NV) centers in a diamond crystal via a frequency-tunable superconducting resonator acting as a quantum bus. Using this circuit, we prepare arbitrary superpositions of the qubit states that we store into collective excitations of the spin ensemble and retrieve back into the qubit. We also report a new method for detecting the magnetic resonance of electronic spins at low temperature with a qubit using the hybrid quantum circuit, as well as our recent progress on spin echo experiments.
Geometric quantum gates for an electron-spin qubit in a quantum dot
Malinovsky, Vladimir; Rudin, Sergey
2012-06-01
A scheme to perform arbitrary unitary operations on a single electron-spin qubit in a quantum dot is proposed. The design is based on the geometrical phase acquired after a cyclic evolution by the qubit state. The scheme is utilizing ultrafast linearly-chirped pulses providing adiabatic excitation of the qubit states and the geometric phase is fully controlled by the relative phase between pulses. The analytic expression of the evolution operator for the electron spin in a quantum dot, which provides a clear geometrical interpretation of the qubit dynamics, is obtained. Using parameters of InGAN/GaN, GaN/AlN quantum dots we provide an estimate for the time scale of the qubit rotations and parameters of the external fields. Robustness of the proposed scheme against external noise is also discussed.
Polyoxometalates as spin qubits
Gaita-Ariño, A.; Aldamen, M.; Clemente-Juan, J.-M.; Coronado, E.; Lehmann, J.; Loss, D.; Stamp, P.
2008-03-01
Polyoxometalates (POMs) are discrete fragments of metal oxides, clusters of regular MOn polyhedra. POMs show a remarkable flexibility in composition, structure and charge state, and thus can be designed according to specific electric and magnetic needs. The two localized spins with S = 1/2 on the V atoms in [PMo12O40(VO)2]^q- can be coupled through the delocalized electrons of the central core. This system was recently used for a theoretical scheme involving two-qubit gates and readout: the electrical manipulation of the molecular redox potential changes the charge of the core and thus the effective magnetic exchange between the qubits. Polyoxometalates can encapsulate magnetic ions, protecting them by a diamagnetic shell of controlled geometry. A great potential of POMs as spin qubits is that they can be constructed using only even elements, such as O, W, Mo and/or Si. Thus, there is a high abundance of polyoxometalate molecules without any nuclear spin, which could result in unusually low decoherence rates. There is currently an effort involving highly anisotropic, high magnetic moment, lanthanide@polyoxometalate molecules acting as spin qubits.
Optical control of electron spin qubit in InAs self-assembled quantum dots
Emary, Clive [TU Berlin, Sekr. PN 7-1, Institut fuer Theoretische Physik, Hardenbergstr. 36, D-10623 Berlin (Germany); Sham, Lu Jeu [Department of Physics, University of California San Diego, La Jolla, California 92093 (United States)
2008-07-01
The spin of an electron trapped in a self-assembled quantum dot is viewed as a promising quantum bit. We present here a theory of the control of such qubits using short laser pulses to excite virtual trion states within the dots. We describe mechanisms for qubit initialisation and for performing universal one and two qubit operations. We show that, for InAs dots, initialisation can be achieved on the nanosecond time-scale, and that coherent operations can performed with laser pulses with durations of tens of picoseconds. These results are of direct relevance to current experiments.
Controllable Quantum State Transfer Between a Josephson Charge Qubit and an Electronic Spin Ensemble
Yan, Run-Ying; Wang, Hong-Ling; Feng, Zhi-Bo
2016-01-01
We propose a theoretical scheme to implement controllable quantum state transfer between a superconducting charge qubit and an electronic spin ensemble of nitrogen-vacancy centers. By an electro-mechanical resonator acting as a quantum data bus, an effective interaction between the charge qubit and the spin ensemble can be achieved in the dispersive regime, by which state transfers are switchable due to the adjustable electrical coupling. With the accessible experimental parameters, we further numerically analyze the feasibility and robustness. The present scheme could provide a potential approach for transferring quantum states controllably with the hybrid system.
Making hybrid [n]-rotaxanes as supramolecular arrays of molecular electron spin qubits
Fernandez, Antonio; Ferrando-Soria, Jesus; Pineda, Eufemio Moreno; Tuna, Floriana; Vitorica-Yrezabal, Iñigo J.; Knappke, Christiane; Ujma, Jakub; Muryn, Christopher A.; Timco, Grigore A.; Barran, Perdita E.; Ardavan, Arzhang; Winpenny, Richard E. P.
2016-01-01
Quantum information processing (QIP) would require that the individual units involved--qubits--communicate to other qubits while retaining their identity. In many ways this resembles the way supramolecular chemistry brings together individual molecules into interlocked structures, where the assembly has one identity but where the individual components are still recognizable. Here a fully modular supramolecular strategy has been to link hybrid organic-inorganic [2]- and [3]-rotaxanes into still larger [4]-, [5]- and [7]-rotaxanes. The ring components are heterometallic octanuclear [Cr7NiF8(O2CtBu)16]- coordination cages and the thread components template the formation of the ring about the organic axle, and are further functionalized to act as a ligand, which leads to large supramolecular arrays of these heterometallic rings. As the rings have been proposed as qubits for QIP, the strategy provides a possible route towards scalable molecular electron spin devices for QIP. Double electron-electron resonance experiments demonstrate inter-qubit interactions suitable for mediating two-qubit quantum logic gates.
Optimization of a solid-state electron spin qubit using gate set tomography
Dehollain, Juan P.; Muhonen, Juha T.; Blume-Kohout, Robin; Rudinger, Kenneth M.; King Gamble, John; Nielsen, Erik; Laucht, Arne; Simmons, Stephanie; Kalra, Rachpon; Dzurak, Andrew S.; Morello, Andrea
2016-10-01
State of the art qubit systems are reaching the gate fidelities required for scalable quantum computation architectures. Further improvements in the fidelity of quantum gates demands characterization and benchmarking protocols that are efficient, reliable and extremely accurate. Ideally, a benchmarking protocol should also provide information on how to rectify residual errors. Gate set tomography (GST) is one such protocol designed to give detailed characterization of as-built qubits. We implemented GST on a high-fidelity electron-spin qubit confined by a single 31P atom in 28Si. The results reveal systematic errors that a randomized benchmarking analysis could measure but not identify, whereas GST indicated the need for improved calibration of the length of the control pulses. After introducing this modification, we measured a new benchmark average gate fidelity of 99.942(8) % , an improvement on the previous value of 99.90(2) % . Furthermore, GST revealed high levels of non-Markovian noise in the system, which will need to be understood and addressed when the qubit is used within a fault-tolerant quantum computation scheme.
Spin-orbit mediated control of spin qubits
Flindt, Christian; Sørensen, A.S; Flensberg, Karsten
2006-01-01
We propose to use the spin-orbit interaction as a means to control electron spins in quantum dots, enabling both single-qubit and two-qubit operations. Very fast single-qubit operations may be achieved by temporarily displacing the electrons. For two-qubit operations the coupling mechanism is based...... on a combination of the spin-orbit coupling and the mutual long-ranged Coulomb interaction. Compared to existing schemes using the exchange coupling, the spin-orbit induced coupling is less sensitive to random electrical fluctuations in the electrodes defining the quantum dots....
Coupling spin qubits via superconductors
Leijnse, Martin; Flensberg, Karsten
2013-01-01
We show how superconductors can be used to couple, initialize, and read out spatially separated spin qubits. When two single-electron quantum dots are tunnel coupled to the same superconductor, the singlet component of the two-electron state partially leaks into the superconductor via crossed...... Andreev reflection. This induces a gate-controlled singlet-triplet splitting which, with an appropriate superconductor geometry, remains large for dot separations within the superconducting coherence length. Furthermore, we show that when two double-dot singlet-triplet qubits are tunnel coupled...... to a superconductor with finite charging energy, crossed Andreev reflection enables a strong two-qubit coupling over distances much larger than the coherence length....
Universal set of single-qubit gates based on geometric phase of electron spin in a quantum dot
Malinovsky, Vladimir; Rudin, Sergey
2012-02-01
The electron spin in a single quantum dot is one of the perspective realizations of a qubit for the implementation of a quantum computer. During last decade several control schemes to perform single gate operations on a single quantum dot spin have been reported. We propose a scheme that allows performing ultrafast arbitrary unitary operations on a single qubit. We demonstrate how to use the geometric phase, which the Bloch vector gains along the cyclic path, to prepare an arbitrary state of a single qubit. It is shown that, the geometrical phase is fully controllable by the relative phase between the external fields. Using the analytic expression of the evolution operator for the electron spin in a quantum dot, we propose a scheme to design a universal set of single-qubit gates based solely on the geometrical phase that the qubit state acquires after a cyclic evolution in the parameter space. The scheme is utilizing ultrafast linearly-chirped pulses providing adiabatic excitation of the qubit states and the geometric phase is fully controlled by the relative phase between pulses.
Circuit quantum electrodynamics with a spin qubit.
Petersson, K D; McFaul, L W; Schroer, M D; Jung, M; Taylor, J M; Houck, A A; Petta, J R
2012-10-18
Electron spins trapped in quantum dots have been proposed as basic building blocks of a future quantum processor. Although fast, 180-picosecond, two-quantum-bit (two-qubit) operations can be realized using nearest-neighbour exchange coupling, a scalable, spin-based quantum computing architecture will almost certainly require long-range qubit interactions. Circuit quantum electrodynamics (cQED) allows spatially separated superconducting qubits to interact via a superconducting microwave cavity that acts as a 'quantum bus', making possible two-qubit entanglement and the implementation of simple quantum algorithms. Here we combine the cQED architecture with spin qubits by coupling an indium arsenide nanowire double quantum dot to a superconducting cavity. The architecture allows us to achieve a charge-cavity coupling rate of about 30 megahertz, consistent with coupling rates obtained in gallium arsenide quantum dots. Furthermore, the strong spin-orbit interaction of indium arsenide allows us to drive spin rotations electrically with a local gate electrode, and the charge-cavity interaction provides a measurement of the resulting spin dynamics. Our results demonstrate how the cQED architecture can be used as a sensitive probe of single-spin physics and that a spin-cavity coupling rate of about one megahertz is feasible, presenting the possibility of long-range spin coupling via superconducting microwave cavities.
Maurand, R.; Jehl, X.; Kotekar-Patil, D.; Corna, A.; Bohuslavskyi, H.; Laviéville, R.; Hutin, L.; Barraud, S.; Vinet, M.; Sanquer, M.; de Franceschi, S.
2016-11-01
Silicon, the main constituent of microprocessor chips, is emerging as a promising material for the realization of future quantum processors. Leveraging its well-established complementary metal-oxide-semiconductor (CMOS) technology would be a clear asset to the development of scalable quantum computing architectures and to their co-integration with classical control hardware. Here we report a silicon quantum bit (qubit) device made with an industry-standard fabrication process. The device consists of a two-gate, p-type transistor with an undoped channel. At low temperature, the first gate defines a quantum dot encoding a hole spin qubit, the second one a quantum dot used for the qubit read-out. All electrical, two-axis control of the spin qubit is achieved by applying a phase-tunable microwave modulation to the first gate. The demonstrated qubit functionality in a basic transistor-like device constitutes a promising step towards the elaboration of scalable spin qubit geometries in a readily exploitable CMOS platform.
High-frequency manipulation of few-electron double quantum dots-toward spin qubits
Kodera, T.; van der Wiel, W. G.; Ono, K.; Sasaki, S.; Fujisawa, T.; Tarucha, S.
2004-04-01
We use a photon-assisted tunneling (PAT) technique to study the high-frequency response of one- and two-electron states in a semiconductor vertically coupled double-dot system. In particular, PAT associated with two-electron spin states in the spin-blockade regime is observed up to the absorption of 10 photons, indicating the preservation of long relaxation times and hence the robustness of our electron spin device under strong microwave irradiation. An alternative double-dot structure with greater flexibility in tuning the inter-dot coupling is presented and its transport characteristics are discussed. This structure is proposed for high-frequency control of two-electron spin states, as required for quantum computation schemes using electron spins in quantum dots.
Adiabatic quantum computing with spin qubits hosted by molecules.
Yamamoto, Satoru; Nakazawa, Shigeaki; Sugisaki, Kenji; Sato, Kazunobu; Toyota, Kazuo; Shiomi, Daisuke; Takui, Takeji
2015-01-28
A molecular spin quantum computer (MSQC) requires electron spin qubits, which pulse-based electron spin/magnetic resonance (ESR/MR) techniques can afford to manipulate for implementing quantum gate operations in open shell molecular entities. Importantly, nuclear spins, which are topologically connected, particularly in organic molecular spin systems, are client qubits, while electron spins play a role of bus qubits. Here, we introduce the implementation for an adiabatic quantum algorithm, suggesting the possible utilization of molecular spins with optimized spin structures for MSQCs. We exemplify the utilization of an adiabatic factorization problem of 21, compared with the corresponding nuclear magnetic resonance (NMR) case. Two molecular spins are selected: one is a molecular spin composed of three exchange-coupled electrons as electron-only qubits and the other an electron-bus qubit with two client nuclear spin qubits. Their electronic spin structures are well characterized in terms of the quantum mechanical behaviour in the spin Hamiltonian. The implementation of adiabatic quantum computing/computation (AQC) has, for the first time, been achieved by establishing ESR/MR pulse sequences for effective spin Hamiltonians in a fully controlled manner of spin manipulation. The conquered pulse sequences have been compared with the NMR experiments and shown much faster CPU times corresponding to the interaction strength between the spins. Significant differences are shown in rotational operations and pulse intervals for ESR/MR operations. As a result, we suggest the advantages and possible utilization of the time-evolution based AQC approach for molecular spin quantum computers and molecular spin quantum simulators underlain by sophisticated ESR/MR pulsed spin technology.
2016-03-31
SECURITY CLASSIFICATION OF: The objective of this project is to implement an electron spin qubit system on a silicon metal-oxide- semiconductor ...Distribution Unlimited UU UU UU UU 31-03-2016 1-Nov-2010 30-Apr-2014 Final Report: Development of a Silicon Metal-Oxide- Semiconductor -Based Qubit Using Spin... Semiconductor -Based Qubit Using Spin Exchange Interactions Alone Report Title The objective of this project is to implement an electron spin qubit system on
Electrically driven spin qubit based on valley mixing
Huang, Wister; Veldhorst, Menno; Zimmerman, Neil M.; Dzurak, Andrew S.; Culcer, Dimitrie
2017-02-01
The electrical control of single spin qubits based on semiconductor quantum dots is of great interest for scalable quantum computing since electric fields provide an alternative mechanism for qubit control compared with magnetic fields and can also be easier to produce. Here we outline the mechanism for a drastic enhancement in the electrically-driven spin rotation frequency for silicon quantum dot qubits in the presence of a step at a heterointerface. The enhancement is due to the strong coupling between the ground and excited states which occurs when the electron wave function overcomes the potential barrier induced by the interface step. We theoretically calculate single qubit gate times tπ of 170 ns for a quantum dot confined at a silicon/silicon-dioxide interface. The engineering of such steps could be used to achieve fast electrical rotation and entanglement of spin qubits despite the weak spin-orbit coupling in silicon.
Phase-Tuned Entangled State Generation between Distant Spin Qubits
Stockill, R.; Stanley, M. J.; Huthmacher, L.; Clarke, E.; Hugues, M.; Miller, A. J.; Matthiesen, C.; Le Gall, C.; Atatüre, M.
2017-07-01
Quantum entanglement between distant qubits is an important feature of quantum networks. Distribution of entanglement over long distances can be enabled through coherently interfacing qubit pairs via photonic channels. Here, we report the realization of optically generated quantum entanglement between electron spin qubits confined in two distant semiconductor quantum dots. The protocol relies on spin-photon entanglement in the trionic Λ system and quantum erasure of the Raman-photon path information. The measurement of a single Raman photon is used to project the spin qubits into a joint quantum state with an interferometrically stabilized and tunable relative phase. We report an average Bell-state fidelity for |ψ(+)⟩ and |ψ(-)⟩ states of 61.6 ±2.3 % and a record-high entanglement generation rate of 7.3 kHz between distant qubits.
Anisotropic Spin Cluster as a Qubit
YAN Xiao-Bo; WANG Ming-Ji
2007-01-01
We study an anisotropic spin cluster of 3 spin S=1/2 particles with antiferromagnetic exchange interaction with non-uniform coupling constants. A time-dependent magnetic field is applied to control the time evolution of the cluster. It is well known that for an odd number og sites a spin cluster qubit can be defined in terms of the ground state doublet. The universal one-qubit logic gate can be constructed from the time evolution operator of the non-autonomous many-body system, and the six basic one-qubit gates can be realized by adjusting the applied time-dependent magnetic field.
Enhancing coherence in molecular spin qubits via atomic clock transitions
Shiddiq, Muhandis; Komijani, Dorsa; Duan, Yan; Gaita-Ariño, Alejandro; Coronado, Eugenio; Hill, Stephen
2016-03-01
Quantum computing is an emerging area within the information sciences revolving around the concept of quantum bits (qubits). A major obstacle is the extreme fragility of these qubits due to interactions with their environment that destroy their quantumness. This phenomenon, known as decoherence, is of fundamental interest. There are many competing candidates for qubits, including superconducting circuits, quantum optical cavities, ultracold atoms and spin qubits, and each has its strengths and weaknesses. When dealing with spin qubits, the strongest source of decoherence is the magnetic dipolar interaction. To minimize it, spins are typically diluted in a diamagnetic matrix. For example, this dilution can be taken to the extreme of a single phosphorus atom in silicon, whereas in molecular matrices a typical ratio is one magnetic molecule per 10,000 matrix molecules. However, there is a fundamental contradiction between reducing decoherence by dilution and allowing quantum operations via the interaction between spin qubits. To resolve this contradiction, the design and engineering of quantum hardware can benefit from a ‘bottom-up’ approach whereby the electronic structure of magnetic molecules is chemically tailored to give the desired physical behaviour. Here we present a way of enhancing coherence in solid-state molecular spin qubits without resorting to extreme dilution. It is based on the design of molecular structures with crystal field ground states possessing large tunnelling gaps that give rise to optimal operating points, or atomic clock transitions, at which the quantum spin dynamics become protected against dipolar decoherence. This approach is illustrated with a holmium molecular nanomagnet in which long coherence times (up to 8.4 microseconds at 5 kelvin) are obtained at unusually high concentrations. This finding opens new avenues for quantum computing based on molecular spin qubits.
Coupling of three-spin qubits to their electric environment
Russ, Maximilian; Ginzel, Florian; Burkard, Guido
2016-10-01
We investigate the behavior of qubits consisting of three electron spins in double and triple quantum dots subject to external electric fields. Our model includes two independent bias parameters, ɛ and ɛM, which both couple to external electromagnetic fields and can be controlled by gate voltages applied to the quantum dot structures. By varying these parameters, one can switch the qubit type by shifting the energies in the single quantum dots, thus changing the electron occupancy in each dot. Starting from the asymmetric resonant exchange qubit with a (2,0,1) and (1,0,2) charge admixture, one can smoothly cross over to the resonant exchange qubit with a detuned (1,1,1) charge configuration, and to the exchange-only qubit with the same charge configuration but equal energy levels down to the hybrid qubits with (1,2,0) and (0,2,1) charge configurations. Here, (l ,m ,n ) describes a configuration with l electrons in the left dot, m electrons in the center dot, and n electrons in the right dot. We first focus on random electromagnetic field fluctuations, i.e., "charge noise," at each quantum dot resulting in dephasing of the qubit, and we provide a complete map of the resulting dephasing time as a function of the bias parameters. We pay special attention to the so-called sweet spots and double sweet spots of the system, which are least susceptible to noise. In the second part, we investigate the coupling of the qubit system to the coherent quantized electromagnetic field in a superconducting strip-line cavity, and we also provide a complete map of the coupling strength as a function of the bias parameters. We analyze the asymmetric qubit-cavity coupling via ɛ and the symmetric coupling via ɛM.
Hybrid spin and valley quantum computing with singlet-triplet qubits.
Rohling, Niklas; Russ, Maximilian; Burkard, Guido
2014-10-24
The valley degree of freedom in the electronic band structure of silicon, graphene, and other materials is often considered to be an obstacle for quantum computing (QC) based on electron spins in quantum dots. Here we show that control over the valley state opens new possibilities for quantum information processing. Combining qubits encoded in the singlet-triplet subspace of spin and valley states allows for universal QC using a universal two-qubit gate directly provided by the exchange interaction. We show how spin and valley qubits can be separated in order to allow for single-qubit rotations.
Coherent Operations and Screening in Multielectron Spin Qubits
Higginbotham, Andrew Patrick; Kuemmeth, Ferdinand; Hanson, M.P.
2014-01-01
Multielectron spin qubits are demonstrated, and performance examined by comparing coherent exchange oscillations in coupled single-electron and multielectron quantum dots, measured in the same device. Fast (>1 GHz) exchange oscillations with a quality factor Q ∼ 15 are found for the multielectron......-independent dephasing is needed to obtain quantitative agreement across a broad parameter range....
Entangling qubits by Heisenberg spin exchange and anyon braiding
Zeuch, Daniel
As the discovery of quantum mechanics signified a revolution in the world of physics more than one century ago, the notion of a quantum computer in 1981 marked the beginning of a drastic change of our understanding of information and computability. In a quantum computer, information is stored using quantum bits, or qubits, which are described by a quantum-mechanical superposition of the quantum states 0 and 1. Computation then proceeds by acting with unitary operations on these qubits. These operations are referred to as quantum logic gates, in analogy to classical computation where bits are acted on by classical logic gates. In order to perform universal quantum computation it is, in principle, sufficient to carry out single-qubit gates and two-qubit gates, where the former act on individual qubits and the latter, acting on two qubits, are used to entangle qubits with each other. The present thesis is divided into two main parts. In the first, we are concerned with spin-based quantum computation. In a spin-based quantum computer, qubits are encoded into the Hilbert space spanned by spin-1/2 particles, such as electron spins trapped in semiconductor quantum dots. For a suitable qubit encoding, turning on-and-off, or "pulsing,'' the isotropic Heisenberg exchange Hamiltonian JSi · Sj allows for universal quantum computation and it is this scheme, known as exchange-only quantum computation, which we focus on. In the second part of this thesis, we consider a topological quantum computer in which qubits are encoded using so-called Fibonacci anyons, exotic quasiparticle excitations that obey non-Abelian statistics, and which may emerge in certain two-dimensional topological systems such as fractional quantum-Hall states. Quantum gates can then be carried out by moving these particles around one another, a process that can be viewed as braiding their 2+1 dimensional worldlines. The subject of the present thesis is the development and theoretical understanding of
Quantum Computing via Singlet-Triplet Spin Qubits in Nanowire Double Quantum Dots
XUE Peng
2011-01-01
We propose a new structure for quantum computing via spin qubits with high fidelity.Each spin qubit corresponds to two electrons in a nanowire double quantum dot,with the singlet and one of the triplets as the logical qubit states.The entangling gate is effected by virtual charge dipole transitions.We include noise to show the feasibility of this scheme under current experimental conditions.
Deterministic doping and the exploration of spin qubits
Schenkel, T.; Weis, C. D.; Persaud, A. [Accelerator and Fusion Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Lo, C. C. [Accelerator and Fusion Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Department of Electrical Engineering and Computer Science, University of California, Berkeley, CA 94720 (United States); London Centre for Nanotechnology (United Kingdom); Chakarov, I. [Global Foundries, Malta, NY 12020 (United States); Schneider, D. H. [Lawrence Livermore National Laboratory, Livermore, CA 94550 (United States); Bokor, J. [Accelerator and Fusion Research Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 (United States); Department of Electrical Engineering and Computer Science, University of California, Berkeley, CA 94720 (United States)
2015-01-09
Deterministic doping by single ion implantation, the precise placement of individual dopant atoms into devices, is a path for the realization of quantum computer test structures where quantum bits (qubits) are based on electron and nuclear spins of donors or color centers. We present a donor - quantum dot type qubit architecture and discuss the use of medium and highly charged ions extracted from an Electron Beam Ion Trap/Source (EBIT/S) for deterministic doping. EBIT/S are attractive for the formation of qubit test structures due to the relatively low emittance of ion beams from an EBIT/S and due to the potential energy associated with the ions' charge state, which can aid single ion impact detection. Following ion implantation, dopant specific diffusion mechanisms during device processing affect the placement accuracy and coherence properties of donor spin qubits. For bismuth, range straggling is minimal but its relatively low solubility in silicon limits thermal budgets for the formation of qubit test structures.
Heo, Jino [College of Electrical and Computer Engineering, Chungbuk National University, Chungdae-ro 1, Seowon-Gu, Cheongju (Korea, Republic of); Kang, Min-Sung [Center for Quantum Information, Korea Institute of Science and Technology (KIST), Seoul, 136-791 (Korea, Republic of); Hong, Chang-Ho [National Security Research Institute, P.O.Box 1, Yuseong, Daejeon, 34188 (Korea, Republic of); Choi, Seong-Gon [College of Electrical and Computer Engineering, Chungbuk National University, Chungdae-ro 1, Seowon-Gu, Cheongju (Korea, Republic of); Hong, Jong-Phil, E-mail: jongph@cbnu.ac.kr [College of Electrical and Computer Engineering, Chungbuk National University, Chungdae-ro 1, Seowon-Gu, Cheongju (Korea, Republic of)
2017-06-15
We propose a scheme for swapping two unknown states of a photon and electron spin confined to a charged quantum dot (QD) between two users by transferring a single photon. This scheme simultaneously transfers and teleports an unknown state (electron spin) between two users. For this bidirectional quantum communication, we utilize the interactions between a photonic and an electron-spin qubits of a QD located inside a single-sided optical cavity. Thus, our proposal using QD-cavity systems can obtain a certain success probability with high fidelity. Furthermore, compared to a previous scheme using cross-Kerr nonlinearities and homodyne detections, our scheme (using QD-cavity systems) can improve the feasibility under the decoherence effect in practice. - Highlights: • Design of Simultaneous quantum transmission and teleportation scheme via quantum dots and cavities. • We have developed the experimental feasibility of this scheme compared with the existing scheme. • Analysis of some benefits when our scheme is experimentally implemented using quantum dots and single-sided cavities.
Shen, Ze-Song; Hong, Fang-Yu
2016-11-01
We present a new scheme for quantum interfaces (QIs) to accomplish the interconversion of photonic qubits and spin qubits based on optomechanical resonators and the spin-orbit-induced interactions in suspended carbon nanotube quantum dots (CNTQDs). This interface implements quantum spin transducers and further enables electrical manipulation of local electron spin qubits, which lays the foundation for all-electrical control of state transfer protocols between two distant quantum nodes in a quantum network. We numerically evaluate the state transfer processes and proceed to estimate the effect of each coupling strength on the operation fidelities. The simulation suggests that high operation fidelities are obtainable under realistic experimental conditions.
Graphene antidot lattices: Designed defects and spin qubits
Pedersen, Thomas; Flindt, Christian; Pedersen, Jesper Goor
2008-01-01
Antidot lattices, defined on a two-dimensional electron gas at a semiconductor heterostructure, are a well-studied class of man-made structures with intriguing physical properties. We point out that a closely related system, graphene sheets with regularly spaced holes ("antidots"), should display...... similar phenomenology, but within a much more favorable energy scale, a consequence of the Dirac fermion nature of the states around the Fermi level. Further, by leaving out some of the holes one can create defect states, or pairs of coupled defect states, which can function as hosts for electron spin...... qubits. We present a detailed study of the energetics of periodic graphene antidot lattices, analyze the level structure of a single defect, calculate the exchange coupling between a pair of spin qubits, and identify possible avenues for further developments....
Tosi, Guilherme, E-mail: g.tosi@unsw.edu.au; Mohiyaddin, Fahd A.; Morello, Andrea, E-mail: a.morello@unsw.edu.au [Centre for Quantum Computation and Communication Technology, School of Electrical Engineering and Telecommunications, UNSW Australia, Sydney, New South Wales 2052, Australia. (Australia); Huebl, Hans [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, D-85748 Garching (Germany); Nanosystems Initiative Munich (NIM), Schellingstr. 4, D-80799 Munich, Germany. (Germany)
2014-08-15
Recent advances in silicon nanofabrication have allowed the manipulation of spin qubits that are extremely isolated from noise sources, being therefore the semiconductor equivalent of single atoms in vacuum. We investigate the possibility of directly coupling an electron spin qubit to a superconducting resonator magnetic vacuum field. By using resonators modified to increase the vacuum magnetic field at the qubit location, and isotopically purified {sup 28}Si substrates, it is possible to achieve coupling rates faster than the single spin dephasing. This opens up new avenues for circuit-quantum electrodynamics with spins, and provides a pathway for dispersive read-out of spin qubits via superconducting resonators.
Guilherme Tosi
2014-08-01
Full Text Available Recent advances in silicon nanofabrication have allowed the manipulation of spin qubits that are extremely isolated from noise sources, being therefore the semiconductor equivalent of single atoms in vacuum. We investigate the possibility of directly coupling an electron spin qubit to a superconducting resonator magnetic vacuum field. By using resonators modified to increase the vacuum magnetic field at the qubit location, and isotopically purified 28Si substrates, it is possible to achieve coupling rates faster than the single spin dephasing. This opens up new avenues for circuit-quantum electrodynamics with spins, and provides a pathway for dispersive read-out of spin qubits via superconducting resonators.
Flying spin-qubit gates implemented through Dresselhaus and Rashba spin orbit couplings
Gong, S. J.; Yang, Z. Q.
2007-07-01
A theoretical scheme is proposed to implement flying spin-qubit gates based on two semiconductor wires with Dresselhaus and Rashba spin orbit couplings (SOCs), respectively. It is found that under the manipulation of the Dresselhaus/Rashba SOC, spin rotates around x/y axis in the three-dimensional spin space. By combining the two kinds of manipulations, i.e. connecting the two kinds of semiconductor wires in series, we obtain a universal set of losses flying single-qubit gates including Hadamard, phase, and π/8 gates. A ballistic switching effect of electronic flow is also found in the investigation. Our results may be useful in future spin or nanoscale electronics.
Exchange-only singlet-only spin qubit
Sala, Arnau; Danon, Jeroen
2017-06-01
We propose a feasible and scalable quantum-dot-based implementation of a singlet-only spin qubit which is to leading order intrinsically insensitive to random effective magnetic fields set up by fluctuating nuclear spins in the host semiconductor. Our proposal thus removes an important obstacle for further improvement of spin qubits hosted in high-quality III-V semiconductors such as GaAs. We show how the resulting qubit could be initialized, manipulated, and read out by electrical means only, in a way very similar to a triple-dot exchange-only spin qubit. Due to the intrinsic elimination of the effective nuclear fields from the qubit Hamiltonian, we find an improvement of the dephasing time T2* of several orders of magnitude as compared to similar existing spin qubits.
Nonlocal entanglement and noise between spin qubits induced by Majorana bound states
Ke, Sha-Sha [State Key Laboratory of Electronic Thin Films and Integrated Devices and School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Lü, Hai-Feng, E-mail: lvhf81@gmail.com [State Key Laboratory of Electronic Thin Films and Integrated Devices and School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Department of Physics, The University of Hong Kong, Pokfulam Road, Hong Kong (China); Yang, Hua-Jun [State Key Laboratory of Electronic Thin Films and Integrated Devices and School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China); Guo, Yong [Department of Physics and State Key Laboratory of Low-Dimensional Quantum Physics, Tsinghua University, Beijing 100084 (China); Collaborative Innovation Center of Quantum Matter, Beijing (China); Zhang, Huai-Wu [State Key Laboratory of Electronic Thin Films and Integrated Devices and School of Physical Electronics, University of Electronic Science and Technology of China, Chengdu 610054 (China)
2015-01-23
We propose a scheme to create nonlocal entanglement between two spatially separated electron spin qubits by coupling them with a pair of Majorana bound states (MBSs). The spin qubits are based on the spins of electrons confined in quantum dots. It is shown that spin entanglement between two dots could be generated by the nonlocality of MBSs. We also demonstrate that in the transport regime, the current noise cross correlation can serve as a good indicator of spin entanglement. The Majorana-dot coupling not only induces an indirect interaction between qubits, but also produces spin localization in the strong coupling limit. These two competing effects lead to a nonmonotonic dependence of current cross-correlation and entanglement on the Majorana-qubit coupling strength. - Highlights: • We propose a scheme to create nonlocal entanglement between two spatially separated electron spin qubits by coupling them with a pair of Majorana bound states. • Spin entanglement between two dots could be generated by the nonlocality of MBSs. • The current noise cross correlation can serve as a good indicator of spin entanglement.
Long-distance entanglement of spin qubits via quantum Hall edge states
Yang, Guang; Hsu, Chen-Hsuan; Stano, Peter; Klinovaja, Jelena; Loss, Daniel
2016-02-01
The implementation of a functional quantum computer involves entangling and coherent manipulation of a large number of qubits. For qubits based on electron spins confined in quantum dots, which are among the most investigated solid-state qubits at present, architectural challenges are often encountered in the design of quantum circuits attempting to assemble the qubits within the very limited space available. Here, we provide a solution to such challenges based on an approach to realizing entanglement of spin qubits over long distances. We show that long-range Ruderman-Kittel-Kasuya-Yosida interaction of confined electron spins can be established by quantum Hall edge states, leading to an exchange coupling of spin qubits. The coupling is anisotropic and can be either Ising type or XY type, depending on the spin polarization of the edge state. Such a property, combined with the dependence of the electron spin susceptibility on the chirality of the edge state, can be utilized to gain valuable insights into the topological nature of various quantum Hall states.
Notch filtering the nuclear environment of a spin qubit.
Malinowski, Filip K; Martins, Frederico; Nissen, Peter D; Barnes, Edwin; Cywiński, Łukasz; Rudner, Mark S; Fallahi, Saeed; Gardner, Geoffrey C; Manfra, Michael J; Marcus, Charles M; Kuemmeth, Ferdinand
2017-01-01
Electron spins in gate-defined quantum dots provide a promising platform for quantum computation. In particular, spin-based quantum computing in gallium arsenide takes advantage of the high quality of semiconducting materials, reliability in fabricating arrays of quantum dots and accurate qubit operations. However, the effective magnetic noise arising from the hyperfine interaction with uncontrolled nuclear spins in the host lattice constitutes a major source of decoherence. Low-frequency nuclear noise, responsible for fast (10 ns) inhomogeneous dephasing, can be removed by echo techniques. High-frequency nuclear noise, recently studied via echo revivals, occurs in narrow-frequency bands related to differences in Larmor precession of the three isotopes (69)Ga, (71)Ga and (75)As (refs 15,16,17). Here, we show that both low- and high-frequency nuclear noise can be filtered by appropriate dynamical decoupling sequences, resulting in a substantial enhancement of spin qubit coherence times. Using nuclear notch filtering, we demonstrate a spin coherence time (T2) of 0.87 ms, five orders of magnitude longer than typical exchange gate times, and exceeding the longest coherence times reported to date in Si/SiGe gate-defined quantum dots.
Notch filtering the nuclear environment of a spin qubit
Malinowski, Filip K.; Martins, Frederico; Nissen, Peter D.; Barnes, Edwin; Cywiński, Łukasz; Rudner, Mark S.; Fallahi, Saeed; Gardner, Geoffrey C.; Manfra, Michael J.; Marcus, Charles M.; Kuemmeth, Ferdinand
2017-01-01
Electron spins in gate-defined quantum dots provide a promising platform for quantum computation. In particular, spin-based quantum computing in gallium arsenide takes advantage of the high quality of semiconducting materials, reliability in fabricating arrays of quantum dots and accurate qubit operations. However, the effective magnetic noise arising from the hyperfine interaction with uncontrolled nuclear spins in the host lattice constitutes a major source of decoherence. Low-frequency nuclear noise, responsible for fast (10 ns) inhomogeneous dephasing, can be removed by echo techniques. High-frequency nuclear noise, recently studied via echo revivals, occurs in narrow-frequency bands related to differences in Larmor precession of the three isotopes 69Ga, 71Ga and 75As (refs 15,16,17). Here, we show that both low- and high-frequency nuclear noise can be filtered by appropriate dynamical decoupling sequences, resulting in a substantial enhancement of spin qubit coherence times. Using nuclear notch filtering, we demonstrate a spin coherence time (T2) of 0.87 ms, five orders of magnitude longer than typical exchange gate times, and exceeding the longest coherence times reported to date in Si/SiGe gate-defined quantum dots.
Landau-Zener transitions in spin qubit encoded in three quantum dots
Łuczak, Jakub; Bułka, Bogdan R.
2017-01-01
We study generation and dynamics of an exchange spin qubit encoded in three coherently coupled quantum dots with three electrons. For two geometries of the system, a linear and a triangular one, the creation and coherent control of the qubit states are performed by the Landau-Zener transitions. In the triangular case, both the qubit states are equivalent and can be easily generated for particular symmetries of the system. If one of the dots is smaller than the others, one can observe Rabi oscillations that can be used for coherent manipulation of the qubit states. The linear system is easier to fabricate; however, then the qubit states are not equivalent, making qubit operations more difficult to control.
Interfacing spin qubits in quantum dots and donors—hot, dense, and coherent
Vandersypen, L. M. K.; Bluhm, H.; Clarke, J. S.; Dzurak, A. S.; Ishihara, R.; Morello, A.; Reilly, D. J.; Schreiber, L. R.; Veldhorst, M.
2017-09-01
Semiconductor spins are one of the few qubit realizations that remain a serious candidate for the implementation of large-scale quantum circuits. Excellent scalability is often argued for spin qubits defined by lithography and controlled via electrical signals, based on the success of conventional semiconductor integrated circuits. However, the wiring and interconnect requirements for quantum circuits are completely different from those for classical circuits, as individual direct current, pulsed and in some cases microwave control signals need to be routed from external sources to every qubit. This is further complicated by the requirement that these spin qubits currently operate at temperatures below 100 mK. Here, we review several strategies that are considered to address this crucial challenge in scaling quantum circuits based on electron spin qubits. Key assets of spin qubits include the potential to operate at 1 to 4 K, the high density of quantum dots or donors combined with possibilities to space them apart as needed, the extremely long-spin coherence times, and the rich options for integration with classical electronics based on the same technology.
Tunable Spin-Qubit Coupling Mediated by a Multielectron Quantum Dot
Srinivasa, V.; Xu, H.; Taylor, J. M.
2015-06-01
We present an approach for entangling electron spin qubits localized on spatially separated impurity atoms or quantum dots via a multielectron, two-level quantum dot. The effective exchange interaction mediated by the dot can be understood as the simplest manifestation of Ruderman-Kittel-Kasuya-Yosida exchange, and can be manipulated through gate voltage control of level splittings and tunneling amplitudes within the system. This provides both a high degree of tunability and a means for realizing high-fidelity two-qubit gates between spatially separated spins, yielding an experimentally accessible method of coupling donor electron spins in silicon via a hybrid impurity-dot system.
Wei, Hai-Rui; Deng, Fu-Guo
2014-12-18
Quantum logic gates are the key elements in quantum computing. Here we investigate the possibility of achieving a scalable and compact quantum computing based on stationary electron-spin qubits, by using the giant optical circular birefringence induced by quantum-dot spins in double-sided optical microcavities as a result of cavity quantum electrodynamics. We design the compact quantum circuits for implementing universal and deterministic quantum gates for electron-spin systems, including the two-qubit CNOT gate and the three-qubit Toffoli gate. They are compact and economic, and they do not require additional electron-spin qubits. Moreover, our devices have good scalability and are attractive as they both are based on solid-state quantum systems and the qubits are stationary. They are feasible with the current experimental technology, and both high fidelity and high efficiency can be achieved when the ratio of the side leakage to the cavity decay is low.
Universal control and error correction in multi-qubit spin registers in diamond.
Taminiau, T H; Cramer, J; van der Sar, T; Dobrovitski, V V; Hanson, R
2014-03-01
Quantum registers of nuclear spins coupled to electron spins of individual solid-state defects are a promising platform for quantum information processing. Pioneering experiments selected defects with favourably located nuclear spins with particularly strong hyperfine couplings. To progress towards large-scale applications, larger and deterministically available nuclear registers are highly desirable. Here, we realize universal control over multi-qubit spin registers by harnessing abundant weakly coupled nuclear spins. We use the electron spin of a nitrogen-vacancy centre in diamond to selectively initialize, control and read out carbon-13 spins in the surrounding spin bath and construct high-fidelity single- and two-qubit gates. We exploit these new capabilities to implement a three-qubit quantum-error-correction protocol and demonstrate the robustness of the encoded state against applied errors. These results transform weakly coupled nuclear spins from a source of decoherence into a reliable resource, paving the way towards extended quantum networks and surface-code quantum computing based on multi-qubit nodes.
Impact of g -factors and valleys on spin qubits in a silicon double quantum dot
Hwang, J. C. C.; Yang, C. H.; Veldhorst, M.; Hendrickx, N.; Fogarty, M. A.; Huang, W.; Hudson, F. E.; Morello, A.; Dzurak, A. S.
2017-07-01
We define single electron spin qubits in a silicon metal-oxide-semiconductor double quantum dot system. By mapping the qubit resonance frequency as a function of a gate-induced electric field, the spectrum reveals an anticrossing that is consistent with an intervalley spin-orbit coupling. We fit the data from which we extract an intervalley coupling strength of 43 MHz. In addition, we observe a narrow resonance near the primary qubit resonance when we operate the device in the (1 ,1 ) charge configuration. The experimental data are consistent with a simulation involving two weakly exchanged-coupled spins with a Zeeman energy difference of 1 MHz, of the same order as the Rabi frequency. We conclude that the narrow resonance is the result of driven transitions between the T- and T+ triplet states, using an electron spin resonance signal of frequency located halfway between the resonance frequencies of the two individual spins. The findings presented here offer an alternative method of implementing two-qubit gates, of relevance to the operation of larger-scale spin qubit systems.
Spin Qubits in GaAs Heterostructures and Gating of InAs Nanowires for Lowtemperature Measurements
Nissen, Peter Dahl
"Spintronics" is used to describes electronics based on control over the spin of the electron rather than the charge; instead of having the charge as the carrier of information, the electrons spin-state should be the target for control and detection in a given device. The spin qubit, one...... of the contenders in the race to build a large-scale quantum computer, is such a component, and research aiming to build, manipulate and couple spin qubits is looking at many materials systems to nd one where the requirements for fast control and long coherence time can be combined with ecient coupling between...... distant qubits. This thesis presents electric measurement on two of the materials systems currently at the forefront of the spin qubit race, namely InAs nanowires and GaAs/AlGaAs heterostructures. For the InAs nanowires we investigate dierent gating geometries towards the goal of dening stable quantum...
Electric nonadiabatic geometric entangling gates on spin qubits
Azimi Mousolou, Vahid
2017-07-01
Producing and maintaining entanglement reside at the heart of the optimal construction of quantum operations and are fundamental issues in the realization of universal quantum computation. We here introduce a setup of spin qubits that allows the geometric implementation of entangling gates between the register qubits with any arbitrary entangling power. We show this by demonstrating a circuit through a spin chain, which performs universal nonadiabatic holonomic two-qubit entanglers. The proposed gates are all electric and geometric, which would help to realize fast and robust entangling gates on spin qubits. This family of entangling gates contains gates that are as efficient as the cnot gate in quantum algorithms. We examine the robustness of the circuit to some extent.
Buhrman, Robert; Daughton, James; Molnár, Stephan; Roukes, Michael
2004-01-01
This report is a comparative review of spin electronics ("spintronics") research and development activities in the United States, Japan, and Western Europe conducted by a panel of leading U.S. experts in the field. It covers materials, fabrication and characterization of magnetic nanostructures, magnetism and spin control in magnetic nanostructures, magneto-optical properties of semiconductors, and magnetoelectronics and devices. The panel's conclusions are based on a literature review and a series of site visits to leading spin electronics research centers in Japan and Western Europe. The panel found that Japan is clearly the world leader in new material synthesis and characterization; it is also a leader in magneto-optical properties of semiconductor devices. Europe is strong in theory pertaining to spin electronics, including injection device structures such as tunneling devices, and band structure predictions of materials properties, and in development of magnetic semiconductors and semiconductor heterost...
Implementation of the Fredkin gate with a three-qubit mixed-spin Heisenberg model
无
2010-01-01
We show that a local unitary(LU) equivalent Fredkin gate can be obtained from the free evolution of three mixed-spin qubits by virtue of numerical simulation with only one step.The spin-1 qubit acts as the control qubit,and two spin-1/2 qubits,which interact with the spin-1 qubit via the first neighbor spin interaction,respectively,play the role of target qubits.We also examine the imperfect Fredkin gate operation by considering the effects of nonidentical coupling constants,uniform and inhomogeneous magnetic fields.
Two-Qubit Geometric Phase Gate for Quantum Dot Spins using Cavity Polariton Resonance
Puri, Shruti; Yamamoto, Yoshihisa
2012-01-01
We describe a design to implement a two-qubit geometric phase gate, by which a pair of electrons confined in adjacent quantum dots are entangled. The entanglement is a result of the Coulomb exchange interaction between the optically excited exciton-polaritons and the localized spins. This optical coupling, resembling the electron-electron Ruderman-Kittel-Kasuya-Yosida (RKKY) inter- actions, offers high speed, high fidelity two-qubit gate operation with moderate cavity quality factor Q. The errors due to the finite lifetime of the polaritons can be minimized by optimizing the optical pulse parameters (duration and energy). The proposed design, using electrostatic quantum dots, maximizes entanglement and ensures scalability.
Spin Qubits in GaAs Heterostructures and Gating of InAs Nanowires for Lowtemperature Measurements
Nissen, Peter Dahl
in lateral quantum dots. First, we incorporate ferromagnetic metal in the depletion gates making them double as micro-magnets supplying magnetic eld gradients allowing spin qubit operation. We demonstrate full tunability of the electron occupation with the magnetic gate structure, combined with a magnetic......"Spintronics" is used to describes electronics based on control over the spin of the electron rather than the charge; instead of having the charge as the carrier of information, the electrons spin-state should be the target for control and detection in a given device. The spin qubit, one...... of the contenders in the race to build a large-scale quantum computer, is such a component, and research aiming to build, manipulate and couple spin qubits is looking at many materials systems to nd one where the requirements for fast control and long coherence time can be combined with ecient coupling between...
Electron Spins in Semiconductor Quantum Dots
Hanson, R.
2005-01-01
This thesis describes a series of experiments aimed at understanding and controlling the behavior of the spin degree of freedom of single electrons, confined in semiconductor quantum dots. This research work is motivated by the prospects of using the electron spin as a quantum bit (qubit), the basic
Accuracy of circular polarization as a measure of spin polarization in quantum dot qubits.
Pryor, C E; Flatté, M E
2003-12-19
A quantum dot spin light emitting diode provides a test of carrier spin injection into a qubit and a means for analyzing carrier spin injection and local spin polarization. Even with 100% spin-polarized carriers the emitted light may be only partially circularly polarized due to the geometry of the dot. We have calculated carrier polarization-dependent optical matrix elements for InAs/GaAs self-assembled quantum dots (SAQDs) for electron and hole spin injection into a range of quantum dot sizes and shapes, and for arbitrary emission directions. Calculations for typical SAQD geometries with emission along [110] show light that is only 5% circularly polarized for spin states that are 100% polarized along [110]. Measuring along the growth direction gives near unity conversion of spin to photon polarization and is the least sensitive to uncertainties in SAQD geometry.
Farberovich, Oleg V.; Mazalova, Victoria L.; Soldatov, Alexander V.
2015-11-01
We present here the quantum model of a Ni solid-state electron spin qubit on a silicon surface with the use of a density-functional scheme for the calculation of the exchange integrals in the non-collinear spin configurations in the generalized spin Hamiltonian (GSH) with the anisotropic exchange coupling parameters linking the nickel ions with a silicon substrate. In this model the interaction of a spin qubit with substrate is considered in GSH at the calculation of exchange integrals Jij of the nanosystem Ni7-Si in the one-electron approach taking into account chemical bonds of all Si-atoms of a substrate (environment) with atoms of the Ni7-cluster. The energy pattern was found from the effective GSH Hamiltonian acting in the restricted spin space of the Ni ions by the application of the irreducible tensor operators (ITO) technique. In this paper we offer the model of the quantum solid-state N-spin qubit based on the studying of the spin structure and the spin-dynamics simulations of the 3d-metal Ni clusters on the silicon surface. The solution of the problem of the entanglement between spin states in the N-spin systems is becoming more interesting when considering clusters or molecules with a spectral gap in their density of states. For quantifying the distribution of the entanglement between the individual spin eigenvalues (modes) in the spin structure of the N-spin system we use the density of entanglement (DOE). In this study we have developed and used the advanced high-precision numerical techniques to accurately assess the details of the decoherence process governing the dynamics of the N-spin qubits interacting with a silicon surface. We have studied the Rabi oscillations to evaluate the N-spin qubits system as a function of the time and the magnetic field. We have observed the stabilized Rabi oscillations and have stabilized the quantum dynamical qubit state and Rabi driving after a fixed time (0.327 μs). The comparison of the energy pattern with the
Characterizing Si:P quantum dot qubits with spin resonance techniques
Wang, Yu; Chen, Chin-Yi; Klimeck, Gerhard; Simmons, Michelle Y.; Rahman, Rajib
2016-01-01
Quantum dots patterned by atomically precise placement of phosphorus donors in single crystal silicon have long spin lifetimes, advantages in addressability, large exchange tunability, and are readily available few-electron systems. To be utilized as quantum bits, it is important to non-invasively characterise these donor quantum dots post fabrication and extract the number of bound electron and nuclear spins as well as their locations. Here, we propose a metrology technique based on electron spin resonance (ESR) measurements with the on-chip circuitry already needed for qubit manipulation to obtain atomic scale information about donor quantum dots and their spin configurations. Using atomistic tight-binding technique and Hartree self-consistent field approximation, we show that the ESR transition frequencies are directly related to the number of donors, electrons, and their locations through the electron-nuclear hyperfine interaction. PMID:27550779
Entanglement and discord for qubits and higher spin systems
A R P Rau
2014-08-01
We discuss aspects of entanglement and quantum discord, two of the quantum correlations that are of much interest in the field of quantum information. Their definitions and handling will be discussed, with simple illustrative examples. A specific example is of entanglement decay resulting from a simple dissipative process and how to alter that decay. An analytical prescription for computing quantum discord when a qubit (spin-1/2 or two-level quantum system) is involved is presented along with applications, and its generalization to higher spins (many levels) indicated.
Dynamics of Genuine Three-Qubit Entanglement in Ising Spin Systems
PANG Chao-Yang; LI Yu-Liang
2006-01-01
We investigate the dynamics of genuine three-qubit entanglement in the Ising model of three spins. A scheme is presented for generating the genuine three-qubit entanglement by the nearest-neighbour couplings. The effect of magnetic fields on the dynamics of genuine three-qubit entanglement is also discussed.
Efficient controlled-phase gate for single-spin qubits in quantum dots
Meunier, T.; Calado, V.E.; Vandersypen, L.M.K.
2011-01-01
Two-qubit interactions are at the heart of quantum information processing. For single-spin qubits in semiconductor quantum dots, the exchange gate has always been considered the natural two-qubit gate. The recent integration of a magnetic field or g-factor gradients in coupled quantum dot systems
Employing Forbidden Transitions as Qubits in a Nuclear Spin-Free Chromium Complex.
Fataftah, Majed S; Zadrozny, Joseph M; Coste, Scott C; Graham, Michael J; Rogers, Dylan M; Freedman, Danna E
2016-02-01
The implementation of quantum computation (QC) would revolutionize scientific fields ranging from encryption to quantum simulation. One intuitive candidate for the smallest unit of a quantum computer, a qubit, is electronic spin. A prominent proposal for QC relies on high-spin magnetic molecules, where multiple transitions between the many MS levels are employed as qubits. Yet, over a decade after the original notion, the exploitation of multiple transitions within a single manifold for QC remains unrealized in these high-spin species due to the challenge of accessing forbidden transitions. To create a proof-of-concept system, we synthesized the novel nuclear spin-free complex [Cr(C3S5)3](3-) with precisely tuned zero-field splitting parameters that create two spectroscopically addressable transitions, with one being a forbidden transition. Pulsed electron paramagnetic resonance (EPR) measurements enabled the investigation of the coherent lifetimes (T2) and quantum control (Rabi oscillations) for two transitions, one allowed and one forbidden, within the S = (3)/2 spin manifold. This investigation represents a step forward in the development of high-spin species as a pathway to scalable QC systems within magnetic molecules.
An Electron-Nucleon Double Spin Solid-State Quantum Computer
Long, G L; Chen, H M; Long, Gui Lu; Ma, Ying-Jun; Chen, Hao-Ming
2003-01-01
An electron-nucleon double spin(ENDOS) solid-state quantum computer scheme is proposed. In this scheme, the qubits are the nuclear spins of phosphorus ion implanted on the (111) surface of $^{28}$Si substrate. An $^{13}$C atom on a scanning tunnelling probe tip is used both to complete single qubit and two-qubit control-not operation, and single qubit measurement. The scheme does not require interactions between qubits, and can accomplish two qubits without the use of SWAP gate. This scheme is scalable, and can be implemented with present-day or near-future technologies.
Reboiro, M., E-mail: reboiro@fisica.unlp.edu.ar [IFLP, CONICET-Department of Physics, University of La Plata, c.c. 67 1900, La Plata (Argentina); Civitarese, O., E-mail: osvaldo.civitarese@fisica.unlp.edu.ar [IFLP, CONICET-Department of Physics, University of La Plata, c.c. 67 1900, La Plata (Argentina); Ramírez, R. [IFLP, CONICET-Department of Mathematics, University of La Plata (Argentina)
2017-03-15
The degree of coherence in a hybrid system composed of superconducting flux-qubits and an electron ensemble is analysed. Both, the interactions among the electrons and among the superconducting flux-qubits are taken into account. The time evolution of the hybrid system is solved exactly, and discussed in terms of the reduced density matrix of each subsystem. It is seen that the inclusion of a line width, for the electrons and for the superconducting flux-qubits, influences the pattern of spin-squeezing and the coherence of the superconducting flux qubits. - Highlights: • The degree of coherence in a hybrid system, composed of superconducting flux qubits and an electron ensemble, is analysed. • The time evolution of the hybrid system is solved exactly and discussed in terms of the reduced density matrix of each subsystem. • It is shown that the initial state of the system evolves to a stationary squeezed state.
Farberovich, Oleg V. [School of Physics and Astronomy, Beverly and Raymond Sackler Faculty of Exact Sciences, Tel Aviv University, Tel Aviv 69978 (Israel); Research Center for Nanoscale Structure of Matter, Southern Federal University, Zorge 5, 344090 Rostov-on-Don (Russian Federation); Voronezh State University, Voronezh 394000 (Russian Federation); Mazalova, Victoria L., E-mail: mazalova@sfedu.ru [Research Center for Nanoscale Structure of Matter, Southern Federal University, Zorge 5, 344090 Rostov-on-Don (Russian Federation); Soldatov, Alexander V. [Research Center for Nanoscale Structure of Matter, Southern Federal University, Zorge 5, 344090 Rostov-on-Don (Russian Federation)
2015-11-15
We present here the quantum model of a Ni solid-state electron spin qubit on a silicon surface with the use of a density-functional scheme for the calculation of the exchange integrals in the non-collinear spin configurations in the generalized spin Hamiltonian (GSH) with the anisotropic exchange coupling parameters linking the nickel ions with a silicon substrate. In this model the interaction of a spin qubit with substrate is considered in GSH at the calculation of exchange integrals J{sub ij} of the nanosystem Ni{sub 7}–Si in the one-electron approach taking into account chemical bonds of all Si-atoms of a substrate (environment) with atoms of the Ni{sub 7}-cluster. The energy pattern was found from the effective GSH Hamiltonian acting in the restricted spin space of the Ni ions by the application of the irreducible tensor operators (ITO) technique. In this paper we offer the model of the quantum solid-state N-spin qubit based on the studying of the spin structure and the spin-dynamics simulations of the 3d-metal Ni clusters on the silicon surface. The solution of the problem of the entanglement between spin states in the N-spin systems is becoming more interesting when considering clusters or molecules with a spectral gap in their density of states. For quantifying the distribution of the entanglement between the individual spin eigenvalues (modes) in the spin structure of the N-spin system we use the density of entanglement (DOE). In this study we have developed and used the advanced high-precision numerical techniques to accurately assess the details of the decoherence process governing the dynamics of the N-spin qubits interacting with a silicon surface. We have studied the Rabi oscillations to evaluate the N-spin qubits system as a function of the time and the magnetic field. We have observed the stabilized Rabi oscillations and have stabilized the quantum dynamical qubit state and Rabi driving after a fixed time (0.327 μs). The comparison of the energy
Quantum entanglement between an optical photon and a solid-state spin qubit.
Togan, E; Chu, Y; Trifonov, A S; Jiang, L; Maze, J; Childress, L; Dutt, M V G; Sørensen, A S; Hemmer, P R; Zibrov, A S; Lukin, M D
2010-08-01
Quantum entanglement is among the most fascinating aspects of quantum theory. Entangled optical photons are now widely used for fundamental tests of quantum mechanics and applications such as quantum cryptography. Several recent experiments demonstrated entanglement of optical photons with trapped ions, atoms and atomic ensembles, which are then used to connect remote long-term memory nodes in distributed quantum networks. Here we realize quantum entanglement between the polarization of a single optical photon and a solid-state qubit associated with the single electronic spin of a nitrogen vacancy centre in diamond. Our experimental entanglement verification uses the quantum eraser technique, and demonstrates that a high degree of control over interactions between a solid-state qubit and the quantum light field can be achieved. The reported entanglement source can be used in studies of fundamental quantum phenomena and provides a key building block for the solid-state realization of quantum optical networks.
Gate-defined quantum dot devices in undoped Si/SiGe heterostructures for spin qubit applications
Volk, Christian; Martins, Frederico; Marcus, Charles M.; Kuemmeth, Ferdinand
Spin qubits based on few electron quantum dots in semiconductor heterostructures are among the most promising systems for realizing quantum computation. Due to its low concentration of nuclear-spin-carrying isotopes, silicon is of special interest as a host material. We characterize gate-defined double and triple quantum dot devices fabricated from undoped Si/Si0.7Ge0.3 heterostructures. Our device architecture is based on integrating all accumulation and depletion mode gates in a single gate layer. This allows us to omit the commonly used global accumulation gate in order to achieve a more local control of the potential landscape in the device. We present our recent progress towards implementing spin qubits in these structures. Support through the EC FP7- ICT project SiSPIN no. 323841, and the Danish National Research Foundation is acknowledged.
Manipulation coherente de qubits de spin dans une boite quantique triple
Gaudreau, Louis
Nous presentons dans cette these une etude detaillee du moment magnetique intrinseque de l'electron, i.e. le spin electronique, incluant la manipulation quantique coherente des etats de spin de trois electrons couples. A cette fin, nous utilisons des boites quantiques laterales pour confiner les electrons. Ces nano-structures, d'une grandeur autour de 1 pm, permettent de confiner un nombre precis d'electrons de facon controlee, allant jusqu'a zero electrons. Les developpements technologiques et d'ingeniosite durant la derniere decennie ont permis de coupler trois boites quantiques, ainsi l'interaction entre plusieurs electrons confines peut etre controlee comme par exemple le couplage quantique tunnel et l'interaction d'echange entre les spins de chacun d'entre eux. A l'aide de boites quantiques couplees, il est possible de realiser des experiences dans plusieurs domaines de la physique moderne : les etats up et down du spin des electrons confines peuvent etre utilisees comme etats quantiques binaires (qubits) dans le domaine de l'informatique quantique, la non-localite quantique peut etre testee en separant spatialement deux electrons enchevetres, il est possible de creer des 'courants de spin enchevetres' utiles en spintronique, et bien d'autres. La manipulation coherente des etats de spin du systeme a trois electrons se fait de facon purement electrique grace a des pulses a haute frequence qui permettent d'augmenter le couplage entre les electrons et de faire la mesure de l'etat resultant apres la manipulation. Nous utilisons l'interaction hyperfine entre les spins des electrons et ceux des noyaux du cristal dans lequel ils resident pour creer les rotations quantiques entre les etats, notamment les etats |Q +3/2> et (D+1/2>. Les resultats obtenus indiquent un temps de coherence de l'ordre de 10 ns. Ces experiences demontrent un niveau de controle sans precedant de boites quantiques triples et pavent la voie vers des nano-structures plus sophistiquees dans
Dynamics and decoherence of a single spin-qubit in a tunable environment
Ratschbacher, L; Carcagni, L; Silver, J M; Zipkes, C; Köhl, M
2013-01-01
We report on the immersion of a spin-qubit encoded in a single trapped ion into a spin-polarized neutral atom environment, which possesses both continuous (motional) and discrete (spin) degrees of freedom. The environment is widely tunable and offers the possibility of a precise microscopic description, both of which allows us to understand dynamics and decoherence from first principles. We observe the spin dynamics of the qubit and measure the decoherence times (T1 and T2), which are determined by the spin-exchange interaction as well as by an unexpectedly strong spin-nonconserving coupling mechanism.
Single-electron Spin Resonance in a Quadruple Quantum Dot
Otsuka, Tomohiro; Nakajima, Takashi; Delbecq, Matthieu R.; Amaha, Shinichi; Yoneda, Jun; Takeda, Kenta; Allison, Giles; Ito, Takumi; Sugawara, Retsu; Noiri, Akito; Ludwig, Arne; Wieck, Andreas D.; Tarucha, Seigo
2016-08-01
Electron spins in semiconductor quantum dots are good candidates of quantum bits for quantum information processing. Basic operations of the qubit have been realized in recent years: initialization, manipulation of single spins, two qubit entanglement operations, and readout. Now it becomes crucial to demonstrate scalability of this architecture by conducting spin operations on a scaled up system. Here, we demonstrate single-electron spin resonance in a quadruple quantum dot. A few-electron quadruple quantum dot is formed within a magnetic field gradient created by a micro-magnet. We oscillate the wave functions of the electrons in the quantum dots by applying microwave voltages and this induces electron spin resonance. The resonance energies of the four quantum dots are slightly different because of the stray field created by the micro-magnet and therefore frequency-resolved addressable control of each electron spin resonance is possible.
Intrinsic errors in transporting a single-spin qubit through a double quantum dot
Li, Xiao; Barnes, Edwin; Kestner, J. P.; Das Sarma, S.
2017-07-01
Coherent spatial transport or shuttling of a single electron spin through semiconductor nanostructures is an important ingredient in many spintronic and quantum computing applications. In this work we analyze the possible errors in solid-state quantum computation due to leakage in transporting a single-spin qubit through a semiconductor double quantum dot. In particular, we consider three possible sources of leakage errors associated with such transport: finite ramping times, spin-dependent tunneling rates between quantum dots induced by finite spin-orbit couplings, and the presence of multiple valley states. In each case we present quantitative estimates of the leakage errors, and discuss how they can be minimized. The emphasis of this work is on how to deal with the errors intrinsic to the ideal semiconductor structure, such as leakage due to spin-orbit couplings, rather than on errors due to defects or noise sources. In particular, we show that in order to minimize leakage errors induced by spin-dependent tunnelings, it is necessary to apply pulses to perform certain carefully designed spin rotations. We further develop a formalism that allows one to systematically derive constraints on the pulse shapes and present a few examples to highlight the advantage of such an approach.
Few-electron Qubits in Silicon Quantum Electronic Devices
2014-09-01
3.1). Ohmic contacts are made by thermally evaporating a 20/1/30/1/70 nm stack of Au/Sb/Au/Sb/Au and annealing at 390 ◦C for 10 min. Low-frequency ac...electron temperature, and Ω = √ ε2 + 4t2c is the qubit energy splitting [45]. With VN = 225 mV, the interdot charge transition is thermally broadened...quantum well layer and ρ is the density of Si. Ξu and Ξd are the shear and dilation potential constants and Q̂ are the phonon unit wave vectors [99]. The
Probing Johnson noise and ballistic transport in normal metals with a single-spin qubit
Kolkowitz, S; Safira, A; High, A. A; Devlin, R. C; Choi, S; Unterreithmeier, Q. P; Patterson, D; Zibrov, A. S; Manucharyan, V. E; Park, H; Lukin, M. D
2015-01-01
.... These fluctuations are intrinsically related to the conductivity of the metal. We use single-spin qubits associated with nitrogen-vacancy centers in diamond to probe Johnson noise in the vicinity of conductive silver films...
Quantum computing with an electron spin ensemble.
Wesenberg, J H; Ardavan, A; Briggs, G A D; Morton, J J L; Schoelkopf, R J; Schuster, D I; Mølmer, K
2009-08-14
We propose to encode a register of quantum bits in different collective electron spin wave excitations in a solid medium. Coupling to spins is enabled by locating them in the vicinity of a superconducting transmission line cavity, and making use of their strong collective coupling to the quantized radiation field. The transformation between different spin waves is achieved by applying gradient magnetic fields across the sample, while a Cooper pair box, resonant with the cavity field, may be used to carry out one- and two-qubit gate operations.
Experimental design of a loophole-free Bell test with spin qubits in diamond
Hensen, Bas; Bernien, Hannes; Dréau, Anaïs; Reiserer, Andreas; Ruitenberg, Just; Blok, Machiel; Wehner, Stephanie; Markham, M.; Twitchen, D.; Hanson, Ronald
2015-03-01
50 years ago, John Bell formulated his famous theorem. The outcomes of independent measurements on entangled objects can reveal strong correlations that violate Bell's inequality. Until now, all experimental implementations of Bell's test required additional assumptions, that open the door for so-called loopholes. These loopholes are particularly important in a cryptography setting where Bell violations enable fully device-independent protocols for quantum key distribution and certified generation of randomness. Here we will present the experimental design of a Bell test, aimed at closing the detection loophole and addressing the locality and free-will loopholes in a single experiment. We use two qubits associated with the electronic spin of the nitrogen-vacancy (NV) center in diamond, separated far enough to allow space-like separation between the two qubits during their measurement. The heralded nature of our remote entanglement protocol and efficient qubit readout allow us to use all entangled pairs, avoiding the fair-sampling assumption. Finally, the free-will loophole is addressed by the use of fast random number generators.
Exact solution of rate equations for a two-spin-qubit system
Le Thi Ha Linh; Nguyen Bich Ha [Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet Road, Cau Giay District, Hanoi (Viet Nam)], E-mail: linhlth@ims.vast.ac.vn
2009-09-01
The quantum dynamics of a system of two interacting spin-qubits is studied for elaborating the physical mechanism of the quantum information transfer between them. A simple model with their Heisenberg XY exchange interaction is investigated. The rate equations are established. The analytical expressions of their solution are exactly derived. They explicitly demonstrate, how the quantum information encoded into a spin-qubit at the initial time t = 0 is transferred to other one at any time t > 0.
Spin Switch and Qubit Register from a Spin Particle Controlled by a Time-Dependent Magnetic Field
WANG Shun-Jin; JIA Cheng-Long; AN Jun-Hong; LUO Hong- Gang
2004-01-01
@@ A spin particle subjected to any time-dependent magnetic field is investigated in detail at different magnetic field configurations. Spin flip probability, spin alignment, cyclic and noncyclic nonadiabatic geometric phases are calculated exactly and their analytical expressions are presented. Our theoretical study shows that a spin particle controlled by a resonant time-dependent magnetic field can be used as efficient controllable devices of spin switch or qubit register.
Spin-orbit qubits of rare-earth-metal ions in axially symmetric crystal fields.
Bertaina, S; Shim, J H; Gambarelli, S; Malkin, B Z; Barbara, B
2009-11-27
Contrary to the well-known spin qubits, rare-earth-metal qubits are characterized by a strong influence of crystal field due to large spin-orbit coupling. At low temperature and in the presence of resonance microwaves, it is the magnetic moment of the crystal-field ground state which nutates (for several micros) and the Rabi frequency Omega(R) is anisotropic. Here, we present a study of the variations of Omega(R)(H(0)) with the magnitude and direction of the static magnetic field H(0) for the odd 167Er isotope in a single crystal CaWO(4):Er(3+). The hyperfine interactions split the Omega(R)(H(0)) curve into eight different curves which are fitted numerically and described analytically. These "spin-orbit qubits" should allow detailed studies of decoherence mechanisms which become relevant at high temperature and open new ways for qubit addressing using properly oriented magnetic fields.
Simulation of micro-magnet stray-field dynamics for spin qubit manipulation
Neumann, R.; Schreiber, L. R., E-mail: lars.schreiber@physik.rwth-aachen.de [Quantum Technology Group, JARA-Institute for Quantum Information, RWTH Aachen University, 52056 Aachen (Germany)
2015-05-21
High-fidelity control and unprecedented long dephasing times in silicon-based single spin qubits have recently confirmed the prospects of solid-state quantum computation. We investigate the feasibility of using a micro-magnet stray field for all-electrical, addressable spin qubit control in a Si/SiGe double quantum dot. For a micro-magnet geometry optimized for high Rabi-frequency, addressability, and robustness to fabrication misalignment as previously demonstrated by Yoneda et al. [Phys. Rev. Lett. 113, 267601 (2014)], we simulate the qubit decoherence due to magnetic stray-field fluctuations, which may dominate in nuclear spin-free systems, e.g., quantum dots in Si/SiGe, Si-MOS structures and (bilayer) graphene. With calculated Rabi-frequencies of 15 MHz, a qubit addressability error below 10{sup −3} is achievable. Magnetic fluctuations from a micro-magnet limits the spin relaxation time to T{sub 1} ≳ 3 s, while pure spin dephasing is negligible. Our results show that micro-magnets are a promising tool for spin qubit computation in nuclear spin-free systems.
Genetic design of enhanced valley splitting towards a spin qubit in silicon
Zhang, Lijun; Luo, Jun-Wei; Saraiva, Andre; Koiller, Belita; Zunger, Alex
2013-09-01
The long spin coherence time and microelectronics compatibility of Si makes it an attractive material for realizing solid-state qubits. Unfortunately, the orbital (valley) degeneracy of the conduction band of bulk Si makes it difficult to isolate individual two-level spin-1/2 states, limiting their development. This degeneracy is lifted within Si quantum wells clad between Ge-Si alloy barrier layers, but the magnitude of the valley splittings achieved so far is small--of the order of 1meV or less--degrading the fidelity of information stored within such a qubit. Here we combine an atomistic pseudopotential theory with a genetic search algorithm to optimize the structure of layered-Ge/Si-clad Si quantum wells to improve this splitting. We identify an optimal sequence of multiple Ge/Si barrier layers that more effectively isolates the electron ground state of a Si quantum well and increases the valley splitting by an order of magnitude, to ~9meV.
Genetic design of enhanced valley splitting towards a spin qubit in silicon.
Zhang, Lijun; Luo, Jun-Wei; Saraiva, Andre; Koiller, Belita; Zunger, Alex
2013-01-01
The long spin coherence time and microelectronics compatibility of Si makes it an attractive material for realizing solid-state qubits. Unfortunately, the orbital (valley) degeneracy of the conduction band of bulk Si makes it difficult to isolate individual two-level spin-1/2 states, limiting their development. This degeneracy is lifted within Si quantum wells clad between Ge-Si alloy barrier layers, but the magnitude of the valley splittings achieved so far is small--of the order of 1 meV or less--degrading the fidelity of information stored within such a qubit. Here we combine an atomistic pseudopotential theory with a genetic search algorithm to optimize the structure of layered-Ge/Si-clad Si quantum wells to improve this splitting. We identify an optimal sequence of multiple Ge/Si barrier layers that more effectively isolates the electron ground state of a Si quantum well and increases the valley splitting by an order of magnitude, to ~9 meV.
Wubs, Martijn
2010-01-01
Qubits driven by resonant strong pulses are studied and a parameter regime is explored in which the dynamics can be solved in closed form. Instantaneous coherent destruction of tunneling can be seen for longer pulses, whereas shorter pulses allow a fast preparation of the qubit state. Results...... are compared with recent experiments of pulsed nitrogen-vacancy center spin qubits in diamond....
Clark, Susan M; Fu, Kai-Mei C; Ladd, Thaddeus D; Yamamoto, Yoshihisa
2007-07-27
We describe a fast quantum computer based on optically controlled electron spins in charged quantum dots that are coupled to microcavities. This scheme uses broadband optical pulses to rotate electron spins and provide the clock signal to the system. Nonlocal two-qubit gates are performed by phase shifts induced by electron spins on laser pulses propagating along a shared waveguide. Numerical simulations of this scheme demonstrate high-fidelity single-qubit and two-qubit gates with operation times comparable to the inverse Zeeman frequency.
Fast long-distance control of spin qubits by photon-assisted cotunneling
Stano, P.; Klinovaja, J.; Braakman, F.R.; Vandersypen, L.M.K.; Loss, D.
2015-01-01
We investigate theoretically the long-distance coupling and spin exchange in an array of quantum dot spin qubits in the presence of microwaves. We find that photon-assisted cotunneling is boosted at resonances between photon and energies of virtually occupied excited states and show how to make it
A fault-tolerant addressable spin qubit in a natural silicon quantum dot.
Takeda, Kenta; Kamioka, Jun; Otsuka, Tomohiro; Yoneda, Jun; Nakajima, Takashi; Delbecq, Matthieu R; Amaha, Shinichi; Allison, Giles; Kodera, Tetsuo; Oda, Shunri; Tarucha, Seigo
2016-08-01
Fault-tolerant quantum computing requires high-fidelity qubits. This has been achieved in various solid-state systems, including isotopically purified silicon, but is yet to be accomplished in industry-standard natural (unpurified) silicon, mainly as a result of the dephasing caused by residual nuclear spins. This high fidelity can be achieved by speeding up the qubit operation and/or prolonging the dephasing time, that is, increasing the Rabi oscillation quality factor Q (the Rabi oscillation decay time divided by the π rotation time). In isotopically purified silicon quantum dots, only the second approach has been used, leaving the qubit operation slow. We apply the first approach to demonstrate an addressable fault-tolerant qubit using a natural silicon double quantum dot with a micromagnet that is optimally designed for fast spin control. This optimized design allows access to Rabi frequencies up to 35 MHz, which is two orders of magnitude greater than that achieved in previous studies. We find the optimum Q = 140 in such high-frequency range at a Rabi frequency of 10 MHz. This leads to a qubit fidelity of 99.6% measured via randomized benchmarking, which is the highest reported for natural silicon qubits and comparable to that obtained in isotopically purified silicon quantum dot-based qubits. This result can inspire contributions to quantum computing from industrial communities.
A fault-tolerant addressable spin qubit in a natural silicon quantum dot
Takeda, Kenta; Kamioka, Jun; Otsuka, Tomohiro; Yoneda, Jun; Nakajima, Takashi; Delbecq, Matthieu R.; Amaha, Shinichi; Allison, Giles; Kodera, Tetsuo; Oda, Shunri; Tarucha, Seigo
2016-01-01
Fault-tolerant quantum computing requires high-fidelity qubits. This has been achieved in various solid-state systems, including isotopically purified silicon, but is yet to be accomplished in industry-standard natural (unpurified) silicon, mainly as a result of the dephasing caused by residual nuclear spins. This high fidelity can be achieved by speeding up the qubit operation and/or prolonging the dephasing time, that is, increasing the Rabi oscillation quality factor Q (the Rabi oscillation decay time divided by the π rotation time). In isotopically purified silicon quantum dots, only the second approach has been used, leaving the qubit operation slow. We apply the first approach to demonstrate an addressable fault-tolerant qubit using a natural silicon double quantum dot with a micromagnet that is optimally designed for fast spin control. This optimized design allows access to Rabi frequencies up to 35 MHz, which is two orders of magnitude greater than that achieved in previous studies. We find the optimum Q = 140 in such high-frequency range at a Rabi frequency of 10 MHz. This leads to a qubit fidelity of 99.6% measured via randomized benchmarking, which is the highest reported for natural silicon qubits and comparable to that obtained in isotopically purified silicon quantum dot–based qubits. This result can inspire contributions to quantum computing from industrial communities. PMID:27536725
Quantum Computing with Electron Spins in Quantum Dots
Vandersypen, L M K; Van Beveren, L H W; Elzerman, J M; Greidanus, J S; De Franceschi, S; Kouwenhoven, Leo P
2002-01-01
We present a set of concrete and realistic ideas for the implementation of a small-scale quantum computer using electron spins in lateral GaAs/AlGaAs quantum dots. Initialization is based on leads in the quantum Hall regime with tunable spin-polarization. Read-out hinges on spin-to-charge conversion via spin-selective tunneling to or from the leads, followed by measurement of the number of electron charges on the dot via a charge detector. Single-qubit manipulation relies on a microfabricated wire located close to the quantum dot, and two-qubit interactions are controlled via the tunnel barrier connecting the respective quantum dots. Based on these ideas, we have begun a series of experiments in order to demonstrate unitary control and to measure the coherence time of individual electron spins in quantum dots.
Spectrum of the Nuclear Environment for GaAs Spin Qubits.
Malinowski, Filip K; Martins, Frederico; Cywiński, Łukasz; Rudner, Mark S; Nissen, Peter D; Fallahi, Saeed; Gardner, Geoffrey C; Manfra, Michael J; Marcus, Charles M; Kuemmeth, Ferdinand
2017-04-28
Using a singlet-triplet spin qubit as a sensitive spectrometer of the GaAs nuclear spin bath, we demonstrate that the spectrum of Overhauser noise agrees with a classical spin diffusion model over 6 orders of magnitude in frequency, from 1 mHz to 1 kHz, is flat below 10 mHz, and falls as 1/f^{2} for frequency f≳1 Hz. Increasing the applied magnetic field from 0.1 to 0.75 T suppresses electron-mediated spin diffusion, which decreases the spectral content in the 1/f^{2} region and lowers the saturation frequency, each by an order of magnitude, consistent with a numerical model. Spectral content at megahertz frequencies is accessed using dynamical decoupling, which shows a crossover from the few-pulse regime (≲16π pulses), where transverse Overhauser fluctuations dominate dephasing, to the many-pulse regime (≳32 π pulses), where longitudinal Overhauser fluctuations with a 1/f spectrum dominate.
2016-09-01
Further support was provided by student interns from the Naval Research Enterprise Internship Program (NREIP) and the SDSU Research Foundation... nuclear spin states of qubits/quantum memory applicable to semiconductor, superconductor, ionic, and superconductor-ionic hybrid technologies. As the...magnetic and nuclear spins of an entangled ensemble or of single spins or photons. These quantum states can be controlled by resonant microwave
Coherence and control of quantum registers based on electronic spin in a nuclear spin bath.
Cappellaro, P; Jiang, L; Hodges, J S; Lukin, M D
2009-05-29
We consider a protocol for the control of few-qubit registers comprising one electronic spin embedded in a nuclear spin bath. We show how to isolate a few proximal nuclear spins from the rest of the bath and use them as building blocks for a potentially scalable quantum information processor. We describe how coherent control techniques based on magnetic resonance methods can be adapted to these solid-state spin systems, to provide not only efficient, high fidelity manipulation but also decoupling from the spin bath. As an example, we analyze feasible performances and practical limitations in the realistic setting of nitrogen-vacancy centers in diamond.
Universal Set of Quantum Gates for Double-Dot Exchange-Only Spin Qubits Under Realistic Conditions
de Michielis, Marco; Ferraro, Elena; Rotta, Davide; Mazzeo, Giovanni; Tagliaferri, Marco; Crippa, Alessandro; Fanciulli, Marco; Prati, Enrico
2014-03-01
We report on a universal set of quantum logic gates for hybrid qubits. In a hybrid qubit the information is encoded in the spin state of three electrons elettrostatically confined in a silicon double quantum dot (QD), in (2,1) filling. All electrical operations, reduced fabrication complexity and high scalability are the strengths of this technology. Schrieffer-Wolff effective models for both one and two coupled hybrid qubit are developed including the inescapable exchange interaction between electrons in the same QD. Optimal sequences of exchange interactions creating a complete set of quantum operations, namely Hadamard, π/8 and CNOT gates, are obtained by using a search algorithm, based on simplex and genetic ones. Silicon devices have been designed by SDFT-based program and efforts in its fabrication have produced in-plane inter-QDs distances down to 100 nm by means of electron beam lithography. Double QDs devices operating in few electron filling regime have been preliminary characterized at 4.2 K. Second affiliation: DSM, Università degli Studi di Milano-Bicocca, Via Cozzi 53, I-20125 Milano, Italy.
Hubert Pascal Seigneur
2010-01-01
Full Text Available We investigate in this paper the dynamics of entanglement between a QD spin qubit and a single photon qubit inside a quantum network node, as well as its robustness against various decoherence processes. First, the entanglement dynamics is considered without decoherence. In the small detuning regime (Δ=78 μeV, there are three different conditions for maximum entanglement, which occur after 71, 93, and 116 picoseconds of interaction time. In the large detuning regime (Δ=1.5 meV, there is only one peak for maximum entanglement occurring at 625 picoseconds. Second, the entanglement dynamics is considered with decoherence by including the effects of spin-nucleus and hole-nucleus hyperfine interactions. In the small detuning regime, a decent amount of entanglement (35% entanglement can only be obtained within 200 picoseconds of interaction. Afterward, all entanglement is lost. In the large detuning regime, a smaller amount of entanglement is realized, namely, 25%. And, it lasts only within the first 300 picoseconds.
Environmental noise effects on entanglement fidelity of exchange-coupled semiconductor spin qubits
Throckmorton, Robert E.; Barnes, Edwin; Das Sarma, S.
2017-02-01
We investigate the effect of magnetic field and charge noise on the generation of entanglement between two Heisenberg exchange-coupled electron spins in a double quantum dot. We focus on exchange-driven evolution that would ideally take an initial unentangled tensor product state to a maximally entangled state in the absence of noise. The presence of noise obviously adversely affects the attainment of maximal entanglement, which we study quantitatively and exactly. To quantify the effects of noise, we calculate two-qubit coherence times and entanglement fidelity, both of which can be extracted from simulations or measurements of the return probability as a function of interaction time, i.e., the time period during which the exchange coupling remains effective between the two spins. We perform these calculations for a broad range of noise strengths that includes the regime of recent experiments. We find that the two types of noise reduce the amount of entanglement in qualitatively distinct ways and that, although charge noise generally leads to faster decoherence, the relative importance of the two types of noise in entanglement creation depends sensitively on the strength of the exchange coupling. Our results can be used to determine the level of noise suppression needed to reach quantum error correction thresholds. We provide quantitative guidance for the requisite noise constraints necessary to eventually reach the >99 % fidelity consistent with the quantum error correction threshold.
Design of a Qubit and a Decoder in Quantum Computing Based on a Spin Field Effect
A. A. Suratgar
2012-04-01
Full Text Available In this paper we present a new method for designing a qubit and decoder in quantum computing based on the field effect in nuclear spin. In this method, the position of hydrogen has been studied in different external fields. The more we have different external field effects and electromagnetic radiation, the more we have different distribution ratios. Consequently, the quality of different distribution ratios has been applied to the suggested qubit and decoder model. We use the nuclear property of hydrogen in order to find a logical truth value. Computational results demonstrate the accuracy and efficiency that can be obtained with the use of these models.
Ultrafast control of electron spin in a quantum dot using geometric phase
Malinovsky, V. S.; Rudin, S.
2012-12-01
We propose a scheme to perform arbitrary unitary operations on a single electron-spin qubit in a quantum dot. The design is solely based on the geometrical phase that the qubit state acquires after a cyclic evolution in the parameter space. The scheme is utilizing ultrafast linearly-chirped pulses providing adiabatic excitation of the qubit states and the geometric phase is fully controlled by the relative phase between pulses. The analytic expression of the evolution operator for the electron spin in a quantum dot, which provides a clear geometrical interpretation of the qubit dynamics is obtained. Using parameters of InGaN/GaN, GaN/AlN quantum dots we provide an estimate for the time scale of the qubit rotations and parameters of the external fields.
Generation of concurrence between two qubits locally coupled to a one-dimensional spin chain
Nag, Tanay; Dutta, Amit
2016-08-01
We consider a generalized central spin model, consisting of two central qubits and an environmental spin chain (with periodic boundary condition) to which these central qubits are locally and weakly connected either at the same site or at two different sites separated by a distance d . Our purpose is to study the subsequent temporal generation of entanglement, quantified by concurrence, when initially the qubits are in an unentangled state. In the equilibrium situation, we show that the concurrence survives for a larger value of d when the environmental spin chain is critical. Importantly, a common feature observed both in the equilibrium and the nonequilibrium situations while the latter is created by a sudden but global change of the environmental transverse field is that the two qubits become maximally entangled for the critical quenching. Following a nonequilibrium evolution of the spin chain, our study for d ≠0 indicates that there exists a threshold time above which concurrence attains a finite value. Additionally, we show that the number of independent decohering channels (DCs) is determined by d as well as the local difference of the transverse field of the two underlying Hamiltonians governing the time evolution; the concurrence can be enhanced by a higher number of independent channels. The qualitatively similar behavior displayed by the concurrence for critical and off-critical quenches, as reported here, is characterized by analyzing the nonequilibrium evolution of these channels. The concurrence is maximum when the decoherence factor or the echo associated with the most rapidly DC decays to zero; on the contrary, the condition when the concurrence vanishes is determined nontrivially by the associated decay of one of the intermediate DCs. Analyzing the reduced density of a single qubit, we also explain the observation that the dephasing rate is always slower than the unentanglement rate. We further establish that the maximally and minimally decohering
Pairwise correlations via quantum discord and its geometric measure in a four-qubit spin chain
Abdel-Baset A. Mohamed
2013-04-01
Full Text Available The dynamic of pairwise correlations, including quantum entanglement (QE and discord (QD with geometric measure of quantum discord (GMQD, are shown in the four-qubit Heisenberg XX spin chain. The results show that the effect of the entanglement degree of the initial state on the pairwise correlations is stronger for alternate qubits than it is for nearest-neighbor qubits. This parameter results in sudden death for QE, but it cannot do so for QD and GMQD. With different values for this entanglement parameter of the initial state, QD and GMQD differ and are sensitive for any change in this parameter. It is found that GMQD is more robust than both QD and QE to describe correlations with nonzero values, which offers a valuable resource for quantum computation.
Single spin detection by qubit SWAP to a molecular nanomagnet
Feng, M
2004-01-01
Spin state detection is a key but very challenging step for any spin-based solid-state quantum computing technology. In fullerene based quantum computer technologies, we here propose to detect the single spin inside a fullerene by transferring the quantum information from the endohedral spin to the ground states of a molecular nanomagnet Fe$_{8}$, with large spin S=10. We show how to perform the required SWAP operation and how to read out the information through state-of-the-art techniques such as micro-SQUID.
Quantum Effects in Higher-Order Correlators of a Quantum-Dot Spin Qubit
Bechtold, A.; Li, F.; Müller, K.; Simmet, T.; Ardelt, P.-L.; Finley, J. J.; Sinitsyn, N. A.
2016-07-01
We measure time correlators of a spin qubit in an optically active quantum dot beyond the second order. Such higher-order correlators are shown to be directly sensitive to pure quantum effects that cannot be explained within the classical framework. They allow direct determination of ensemble and quantum dephasing times, T2* and T2, using only repeated projective measurements and without the need for coherent spin control. Our method enables studies of purely quantum behavior in solid state systems, including tests of the Leggett-Garg type of inequalities that rule out local hidden variable interpretation of the quantum-dot spin dynamics.
Electron spin resonance and spin-valley physics in a silicon double quantum dot.
Hao, Xiaojie; Ruskov, Rusko; Xiao, Ming; Tahan, Charles; Jiang, HongWen
2014-05-14
Silicon quantum dots are a leading approach for solid-state quantum bits. However, developing this technology is complicated by the multi-valley nature of silicon. Here we observe transport of individual electrons in a silicon CMOS-based double quantum dot under electron spin resonance. An anticrossing of the driven dot energy levels is observed when the Zeeman and valley splittings coincide. A detected anticrossing splitting of 60 MHz is interpreted as a direct measure of spin and valley mixing, facilitated by spin-orbit interaction in the presence of non-ideal interfaces. A lower bound of spin dephasing time of 63 ns is extracted. We also describe a possible experimental evidence of an unconventional spin-valley blockade, despite the assumption of non-ideal interfaces. This understanding of silicon spin-valley physics should enable better control and read-out techniques for the spin qubits in an all CMOS silicon approach.
Memory-keeping effects and forgetfulness in the dynamics of a qubit coupled to a spin chain
Apollaro, T J G; Plastina, F; Paternostro, M
2010-01-01
Using recently proposed measures for non-Markovianity [H. P. Breuer, E. M. Laine, and J. Piilo, Phys. Rev. Lett. {\\bf 103}, 210401 (2009)], we study the dynamics of a qubit coupled to a spin environment via an energy-exchange mechanism. We show the existence of a point, in the parameter space of the system, where the qubit dynamics is effectively Markovian and that such a point separates two regions with completely different dynamical behaviors. Indeed, our study demonstrates that the qubit evolution can in principle be tuned from a perfectly forgetful one to a deep non-Markovian regime where the qubit is strongly affected by the dynamical back-action of the environmental spins. By means of quantum process tomography, we provide a complete and intuitive characterization of the qubit channel.
Sudden Death, Birth and Stable Entanglement in a Two-Qubit Heisenberg XY Spin Chain
SHAN Chuan-Jia; CHENG Wei-Wen; LIU Tang-Kun; LIU Ji-Bing; WEI Hua
2008-01-01
Taking the decoherence effect due to population relaxation into account, we investigate the entanglement properties for two qubits in the Heisenberg XY interaction and subject to an external magnetic field. It is found that the phenomenon of entanglement sudden death (ESD) as well as sudden birth (ESB) appear during the evolution process for particular initial states. The influence of the external magnetic field and the spin environment on ESD and ESB are addressed in detail. It is shown that the concurrence, a measure of entanglement, can be controlled by tuning the parameters of the spin chain, such as the anisotropic parameter, external magnetic field, and the coupling strength with their environment. In particular, we find that a critical anisotropy constant exists, above which ESB vanishes while ESD appears. It is also notable that stable entanglement, which is independent of different initial states of the qubits, occurs even in the presence or decoherence.
Dynamic Entanglement Evolution of Two-qubit XYZ Spin Chain in Markovian Environment
Yi-Chong, Ren
2015-01-01
We propose a new approach called Ket-Bra Entangled State (KBES) Method for converting master equation into Schr\\"{o}dinger-like equation. With this method, we investigate decoherence process and entanglement dynamics induced by a $2$-qubit spin chain that each qubit coupled with reservoir. The spin chain is an anisotropy $XYZ$ Heisenberg model in the external magnetic field $B$, the corresponding master equation is solved concisely by KBES method; Furthermore, the effects of anisotropy, temperature, external field and initial state on concurrence dynamics is analyzed in detail for the case that initial state is Extended Wenger-Like(EWL) state. Finally we research the coherence and concurrence of the final state (namely the density operator for time tend to infinite)
Optically controlled spin-glasses generated using multi-qubit cavity systems
Lee, C F; Lee, Chiu Fan; Johnson, Neil F.
2004-01-01
Recent advances in nanofabrication and optical control imply that multi-qubit-cavity systems can now be engineered with pre-designed couplings. Here we propose optical realizations of spin-glass systems which exploit these new nanoscale technologies. By contrast with traditional realizations using magnetic solids, phase transition phenomena can now arise in both the matter and radiation subsystems. Moreover the phase transitions are tunable simply by varying the matter-radiation coupling strength.
Coherent control and detection of spin qubits in semiconductor with magnetic field engineering
Tokura, Yasuhiro
2012-02-01
Electrical control and detection of the spin qubits in semiconductor quantum dots (QDs) are among the major rapidly progressing fields for possible implementation of scalable quantum information processing. Coherent control of one-[1-3] and two-[4,5] spin qubits by electrical means had been demonstrated with various approaches. We have used an engineered magnetic field structure realized with proximal micro-magnets to transduce the spin and charge degrees of freedom and to selectively address one of the two spins [3]. We have demonstrated an all-electrical two-qubit gate consisting of single-spin rotations and interdot spin exchange in double QDs. A partially entangled output state is obtained by the application of the two-qubit gate to an initial, uncorrelated state. Our calculations taking into account of the nuclear spin fluctuation show the degree of entanglement. Non-uniform magnetic field also enables spin selective photon-assisted tunneling in double QDs, which then constitutes non-demolition spin read-out system in combination with a near-by charge detector [6]. [4pt] In collaboration with R. Brunner, Inst. of Phys., Montanuniversitaet Leoben, 8700, Austria, M. Pioro-Ladrière, D'ep. de Phys., Universit'e de Sherbrooke, Sherbrooke, Qu'ebec, J1K-2R1, Canada, T. Kubo, Y. -S. Shin, T. Obata, and S. Tarucha, ICORP-JST and Dep. of Appl. Phys., Univ. of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan.[4pt] [1] F. H. Koppens, et al., Nature 442, 766 (2006).[0pt] [2] K. C. Nowack, et al., Science 318, 1430 (2007).[0pt] [3] M. Pioro-Ladrière, et al., Nature Physics 4, 776 (2008).[0pt] [4] J. R. Petta, et al., Science 309, 2180 (2005).[0pt] [5] R. Brunner, et al., Phys. Rev. Lett. 107, 146801 (2011).[0pt] [6] Y. -S. Shin, et al., Phys. Rev. Lett. 104, 046802 (2010).
Storage of Multiple Coherent Microwave Excitations in an Electron Spin Ensemble
Wu, Hua; George, Richard E.; Wesenberg, Janus H.;
2010-01-01
stored and retrieved. Here we employ holographic techniques to realize a coherent memory using a pulsed magnetic field gradient and demonstrate the storage and retrieval of up to 100 weak 10 GHz coherent excitations in collective states of an electron spin ensemble. We further show that such collective......Strong coupling between a microwave photon and electron spins, which could enable a long-lived quantum memory element for superconducting qubits, is possible using a large ensemble of spins. This represents an inefficient use of resources unless multiple photons, or qubits, can be orthogonally...
Delteil, Aymeric; Sun, Zhe; Fält, Stefan; Imamoğlu, Atac
2017-04-28
Photonic losses pose a major limitation for the implementation of a quantum state transfer between nodes of a quantum network. A measurement that heralds a successful transfer without revealing any information about the qubit may alleviate this limitation. Here, we demonstrate the heralded absorption of a single photonic qubit, generated by a single neutral quantum dot, by a single-electron charged quantum dot that is located 5 m away. The transfer of quantum information to the spin degree of freedom takes place upon the emission of a photon; for a properly chosen or prepared quantum dot, the detection of this photon yields no information about the qubit. We show that this process can be combined with local operations optically performed on the destination node by measuring classical correlations between the absorbed photon color and the final state of the electron spin. Our work suggests alternative avenues for the realization of quantum information protocols based on cascaded quantum systems.
Noise to lubricate qubit transfer in a spin network
Rafiee, Morteza; Lupo, Cosmo; Mancini, Stefano
2013-09-01
We consider quantum state transfer in a fully connected spin network, in which the results indicate that it is impossible to achieve high fidelity by free dynamics. However, the addition of certain kinds of noise can be helpful for this purpose. In fact, we introduce a model of Gaussian white noise affecting the spin-spin couplings (edges), except those linked to the input and output node, and prove that it enhances the fidelity of state transfer. The observed noise benefit is scale free as it applies to a quantum network of any size. The amount of the fidelity enhancement, depending on the noise strength as well as on the number of edges to which it is applied, can be so high as to take the fidelity close to one.
Quantum Entanglement of Quantum Dot Spin Using Flying Qubits
2015-05-01
SPDC photon is teleported to a single quantum dot spin by a projective measurement using a Hong Ou Mandel (HOM) interferometer. The SPDC source...photo diode B: Blue CW: Continuous wave DBR: Distributed Bragg reflector EOM: Electro-optics modulator H: Horizontal HOM: Hong-Ou- Mandel InAs
Coherent manipulation of a ^{40}Ca^{+} spin qubit in a micro ion trap
Poschinger, U.G.; Huber, G.; Ziesel, F.;
2009-01-01
We demonstrate the implementation of a spin qubit with a single 40Ca+ ion in a micro ion trap. The qubit is encoded in the Zeeman ground state levels mJ = +1/2 and mJ = -1/2 of the S1/2 state of the ion. We show sideband cooling close to the vibrational ground state and demonstrate the initializa......We demonstrate the implementation of a spin qubit with a single 40Ca+ ion in a micro ion trap. The qubit is encoded in the Zeeman ground state levels mJ = +1/2 and mJ = -1/2 of the S1/2 state of the ion. We show sideband cooling close to the vibrational ground state and demonstrate...... to extract the phonon number distribution. The dynamics of this distribution is analysed to deduce the trap-induced heating rate of 0.3(1) phonons ms-1....
Zhang, Y. G.; Tang, Z., E-mail: ztang@ee.ecnu.edu.cn; Zhao, X. G.; Cheng, G. D.; Tu, Y.; Cong, W. T.; Zhu, Z. Q.; Chu, J. H. [Key Laboratory of Polar Materials and Devices, Ministry of Education of China, East China Normal University, Shanghai 200241 (China); Peng, W., E-mail: wpeng@ecnu.edu.cn [Supercomputer Center, Administration Department of Equipments, East China Normal University, Shanghai 200062 (China)
2014-08-04
Spintronic and electronic properties of a neutral oxygen-vacancy (O-V) center, an isoelectronic defect similar to the negatively charged nitrogen-vacancy center in diamond, were studied by combining first-principles calculations and a mean-field theory for spin hyperfine interaction. It is elucidated that the neutral O-V center is stable in the p-type diamond and possesses an S = 1 triplet ground state and four spin-conserved excited states with the spin coherence times in an order of second at T = 0 K. The results indicate that the neutral O-V center is another promising candidate for spin coherent manipulation and qubit operation.
Electron spin relaxation in a transition-metal dichalcogenide quantum dot
Pearce, Alexander J.; Burkard, Guido
2017-06-01
We study the relaxation of a single electron spin in a circular quantum dot in a transition-metal dichalcogenide monolayer defined by electrostatic gating. Transition-metal dichalcogenides provide an interesting and promising arena for quantum dot nano-structures due to the combination of a band gap, spin-valley physics and strong spin-orbit coupling. First we will discuss which bound state solutions in different B-field regimes can be used as the basis for qubits states. We find that at low B-fields combined spin-valley Kramers qubits to be suitable, while at large magnetic fields pure spin or valley qubits can be envisioned. Then we present a discussion of the relaxation of a single electron spin mediated by electron-phonon interaction via various different relaxation channels. In the low B-field regime we consider the spin-valley Kramers qubits and include impurity mediated valley mixing which will arise in disordered quantum dots. Rashba spin-orbit admixture mechanisms allow for relaxation by in-plane phonons either via the deformation potential or by piezoelectric coupling, additionally direct spin-phonon mechanisms involving out-of-plane phonons give rise to relaxation. We find that the relaxation rates scale as \\propto B 6 for both in-plane phonons coupling via deformation potential and the piezoelectric effect, while relaxation due to the direct spin-phonon coupling scales independant to B-field to lowest order but depends strongly on device mechanical tension. We will also discuss the relaxation mechanisms for pure spin or valley qubits formed in the large B-field regime.
Geometric Phase for a Qutrit-Qubit Mixed-Spin System
WANG Ai-Ping; QIANG Wen-Chao; LING Ya-Wen; XIN Hong; YANG Yong-Ming
2011-01-01
@@ We study the geometric phase of a qutrit-qubit mixed-spin system in an external homogeneous magnetic field.Both the spin-spin interaction strength J and the external magnetic field B can affect the geometric phase of the system.In addition,we consider the negativity of the composite system.The relationship between the negativity and the geometric phase is obtained.Finally,we calculate the geometric phase for a thermal mixed state and show how the geometric phase depends on the resealed coupling parameter and temperature.In the limit T→0,we can recover the result of the ground state.This analysis has some implications in realistic implementations of geometric quantum computation.
STIC: Development of a System of Nonlocally Interconnected Spin Qubits for Quantum Computation
2012-09-23
Taylor, W. Dür, P. Zoller, A. Yacoby, C. Marcus, M. Lukin. Solid-State Circuit for Spin Entanglement Generation and Purification, Physical Review Letters , (06...Triplet Qubit, Physical Review Letters , (10 2009): 160503. doi: 10.1103/PhysRevLett.103.160503 2012/09/04 08:13:52 16 D. J. Reilly, J. M. Taylor, J...Double Quantum Dot, Physical Review Letters , (07 2006): 0. doi: 10.1103/PhysRevLett.97.056801 2012/09/04 02:25:07 7 J. Taylor, J. Petta, A. Johnson, A
无
2010-01-01
The synthesis of the Toffoli gate, Fredkin gate, three-qubit Inversion-on-equality gate and D(α) gate, as well as their implementation in a three spins system coupled with Ising interaction are investigated. The sequences of the control pulse and the drift process to implement these gates are given. It is revealed that the implementation of some three-qubit gates in a circular spin chain is much better than in a linear spin chain, and every two measurements of the quantum computation complexity are not always consistent. It is significant to directly study the implementation of the multi-qubit gates and even more complicated components of quantum information processing without resorting to their synthesis.
Quantum computing by optical control of electron spins
Liu, Ren-Bao; Sham, L J
2010-01-01
We review the progress and main challenges in implementing large-scale quantum computing by optical control of electron spins in quantum dots (QDs). Relevant systems include self-assembled QDs of III-V or II-VI compound semiconductors (such as InGaAs and CdSe), monolayer fluctuation QDs in compound semiconductor quantum wells, and impurity centers in solids such as P-donors in silicon and nitrogen-vacancy centers in diamond. The decoherence of the electron spin qubits is discussed and various schemes for countering the decoherence problem are reviewed. We put forward designs of local nodes consisting of a few qubits which can be individually addressed and controlled. Remotely separated local nodes are connected by photonic structures (microcavities and waveguides) to form a large-scale distributed quantum system or a quantum network. The operation of the quantum network consists of optical control of a single electron spin, coupling of two spins in a local nodes, optically controlled quantum interfacing betwe...
Control and measurement of electron spins in semiconductor quantum dots
Kouwenhoven, L.P.; Elzerman, J.M.; Hanson, R.; Willems van Beveren, L.H.; Vandersypen, L.M.K. [ERATO Mesoscopic Correlation Project, Delft University of Technology, Delft (Netherlands); Kavli Institute of Nanoscience Delft (Netherlands)
2006-11-15
We present an overview of experimental steps taken towards using the spin of a single electron trapped in a semiconductor quantum dot as a spin qubit [Loss and DiVincenzo, Phys. Rev. A 57, 120 (1998)]. Fabrication and characterization of a double quantum dot containing two coupled spins has been achieved, as well as initialization and single-shot read-out of the spin state. The relaxation time T {sub 1} of single-spin and two-spin states was found to be on the order of a millisecond, dominated by spin-orbit interactions. The time-averaged dephasing time T{sub 2}{sup *}, due to fluctuations in the ensemble of nuclear spins in the host semiconductor, was determined to be on the order of several tens of nanoseconds. Coherent manipulation of single-spin states can be performed using a microfabricated wire located close to the quantum dot, while two-spin interactions rely on controlling the tunnel barrier connecting the respective quantum dots [Petta et al., Science 309, 2180 (2005)]. (copyright 2006 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Extreme Harmonic Generation in an InAs Spin-Orbit Qubit
Stehlik, J.; Schroer, M. D.; Maialle, M. Z.; Degani, M. H.; Petta, J. R.
2014-03-01
Strong spin-orbit materials have shown great promise in the field of quantum computation. Unlike conventional semiconductor materials, fast all-electrical control is achieved through electric dipole spin resonance (EDSR). In this work we explore EDSR in an InAs nanowire spin-orbit qubit. We observe signs of harmonic generation where spin flips occur at the resonance condition nhf = gμB B , where f is the applied frequency, B is the magnetic field, g is the g-factor and n is an integer. Near the interdot charge transition we observe harmonics up to n = 8, indicating extreme harmonic generation. At far detuning we only observe the n = 1 resonance. Further, we find odd/even structure in the harmonic response: odd harmonics result in an increase in the leakage current while even harmonics result in its suppression. Finally we observe oscillations in the resonant current as a function of detuning. The striking detuning dependence suggests that the harmonics may be caused by Landau-Zener transitions occurring due to the anti-crossing between the differing charge states. Numerical simulations of the system are qualitatively consistent with this picture. Funded by the Sloan and Packard Foundations, the NSF, and the Army Research Office. M.Z.M. and M.H.D. were funded by Fundação de Amparo à Pesquisa de São Paulo (Fapesp) and INCT-DISSE/CNPq, Brazil.
Conversion from Single Photon to Single Electron Spin Using Electrically Controllable Quantum Dots
Oiwa, Akira; Fujita, Takafumi; Kiyama, Haruki; Allison, Giles; Ludwig, Arne; Wieck, Andreas D.; Tarucha, Seigo
2017-01-01
Polarization is a fundamental property of light and could provide various solutions to the development of secure optical communications with high capacity and high speed. In particular, the coherent quantum state conversion between single photons and single electron spins is a prerequisite for long-distance quantum communications and distributed quantum computation. Electrically defined quantum dots have already been proven to be suitable for scalable solid state qubits by demonstrations of single-spin coherent manipulations and two-qubit gate operations. Thus, their capacity for quantum information technologies would be considerably extended by the achievement of entanglement between an electron spin in the quantum dots and a photon. In this review paper, we show the basic technologies for trapping single electrons generated by single photons in quantum dots and for detecting their spins using the Pauli effect with sensitive charge sensors.
Electronic spin transport and spin precession in single graphene layers at room temperature.
Tombros, Nikolaos; Jozsa, Csaba; Popinciuc, Mihaita; Jonkman, Harry T; van Wees, Bart J
2007-08-02
Electronic transport in single or a few layers of graphene is the subject of intense interest at present. The specific band structure of graphene, with its unique valley structure and Dirac neutrality point separating hole states from electron states, has led to the observation of new electronic transport phenomena such as anomalously quantized Hall effects, absence of weak localization and the existence of a minimum conductivity. In addition to dissipative transport, supercurrent transport has also been observed. Graphene might also be a promising material for spintronics and related applications, such as the realization of spin qubits, owing to the low intrinsic spin orbit interaction, as well as the low hyperfine interaction of the electron spins with the carbon nuclei. Here we report the observation of spin transport, as well as Larmor spin precession, over micrometre-scale distances in single graphene layers. The 'non-local' spin valve geometry was used in these experiments, employing four-terminal contact geometries with ferromagnetic cobalt electrodes making contact with the graphene sheet through a thin oxide layer. We observe clear bipolar (changing from positive to negative sign) spin signals that reflect the magnetization direction of all four electrodes, indicating that spin coherence extends underneath all of the contacts. No significant changes in the spin signals occur between 4.2 K, 77 K and room temperature. We extract a spin relaxation length between 1.5 and 2 mum at room temperature, only weakly dependent on charge density. The spin polarization of the ferromagnetic contacts is calculated from the measurements to be around ten per cent.
Controllable spin-orbit couplings of trapped electrons for distant quantum manipulations
Zhang, Miao
2012-01-01
Spin-orbit interactions of carriers yield various many-body quantum effects in the semiconducting physics. Here, we propose an approach to coherently manipulate spin-orbit interactions of electrons trapped on the liquid Helium at a single quantum level. The configuration consists of single electrons, confined individually on the liquid Helium by the micro-electrodes, moving along the surface as the harmonic oscillators. The spin of an electron could be coupled to its orbit (i.e., the vibrational motion) by properly applying a magnetic field. Interestingly, a Jaynes-Cummings (JC) type interaction between the spin of an electron and the vibrational motion of another distant electron is induced by virtually exciting the vibrational motion of the electron. With the present JC model, the quantum information processing between the spin qubits of the distant electrons could be effectively realized without moving the electrons. The proposal could be generlizedly applied to the other Fermi-Bosonic systems.
Spin blockade and coherent dynamics of high-spin states in a three-electron double quantum dot
Chen, Bao-Bao; Wang, Bao-Chuan; Cao, Gang; Li, Hai-Ou; Xiao, Ming; Guo, Guang-Can; Jiang, Hong-Wen; Hu, Xuedong; Guo, Guo-Ping
2017-01-01
Asymmetry in a three-electron double quantum dot (DQD) allows spin blockade, when spin-3/2 (quadruplet) states and spin-1/2 (doublet) states have different charge configurations. We have observed this DQD spin blockade near the (1,2)-(2,1) charge transition using a pulsed-gate technique and a charge sensor. We, then, use this spin blockade to detect Landau-Zener-Stückelberg interference and coherent oscillations between the spin quadruplet and doublet states. Such studies add to our understandings of coherence and control properties of three-spin states in a double dot, which, in turn, would benefit explorations into various qubit encoding schemes in semiconductor nanostructures.
Zhang, Kai; Nusran, N. M.; Slezak, B. R.; Gurudev Dutt, M. V.
2016-05-01
While it is often thought that the geometric phase is less sensitive to fluctuations in the control fields, a very general feature of adiabatic Hamiltonians is the unavoidable dynamic phase that accompanies the geometric phase. The effect of control field noise during adiabatic geometric quantum gate operations has not been probed experimentally, especially in the canonical spin qubit system that is of interest for quantum information. We present measurement of the Berry phase and carry out adiabatic geometric phase gate in a single solid-state spin qubit associated with the nitrogen-vacancy center in diamond. We manipulate the spin qubit geometrically by careful application of microwave radiation that creates an effective rotating magnetic field, and observe the resulting Berry phase signal via spin echo interferometry. Our results show that control field noise at frequencies higher than the spin echo clock frequency causes decay of the quantum phase, and degrades the fidelity of the geometric phase gate to the classical threshold after a few (∼10) operations. This occurs inspite of the geometric nature of the state preparation, due to unavoidable dynamic contributions. We have carried out systematic analysis and numerical simulations to study the effects of the control field noise and imperfect driving waveforms on the quantum phase gate.
Noise suppression and long-range exchange coupling for gallium arsenide spin qubits
Malinowski, Filip
to put the highest, up to date, lower bound on the electron spin coherence time in gallium arsenide: 870 ms. Later, we study the perspectives of exploiting a multielectron quantum dot as a mediator of the exchange interaction. We investigate interaction between a single spin and the multelectron quantum...
Electronic structure of spin systems
Saha-Dasgupta, Tanusri
2016-04-15
Highlights: • We review the theoretical modeling of quantum spin systems. • We apply the Nth order muffin-tin orbital electronic structure method. • The method shows the importance of chemistry in the modeling. • CuTe{sub 2}O{sub 5} showed a 2-dimensional coupled spin dimer behavior. • Ti substituted Zn{sub 2}VO(PO{sub 4}){sub 2} showed spin gap behavior. - Abstract: Low-dimensional quantum spin systems, characterized by their unconventional magnetic properties, have attracted much attention. Synthesis of materials appropriate to various classes within these systems has made this field very attractive and a site of many activities. The experimental results like susceptibility data are fitted with the theoretical model to derive the underlying spin Hamiltonian. However, often such a fitting procedure which requires correct guess of the assumed spin Hamiltonian leads to ambiguity in deciding the representative model. In this review article, we will describe how electronic structure calculation within the framework of Nth order muffin-tin orbital (NMTO) based Wannier function technique can be utilized to identify the underlying spin model for a large number of such compounds. We will show examples from compounds belonging to vanadates and cuprates.
Coherent spin control of a nanocavity-enhanced qubit in diamond
Li, Luozhou; Chen, Edward H; Walsh, Michael; Bayn, Igal; Goldstein, Jordan; Gaathon, Ophir; Trusheim, Matthew E; Lu, Ming; Mower, Jacob; Cotlet, Mircea; Markham, Matthew L; Twitchen, Daniel J; Englund, Dirk
2014-01-01
A central aim of quantum information processing is the efficient entanglement of multiple stationary quantum memories via photons. Among solid-state systems, the nitrogen-vacancy (NV) centre in diamond has emerged as an excellent optically addressable memory with second-scale electron spin coherence times. Recently, quantum entanglement and teleportation have been shown between two NV-memories, but scaling to larger networks requires more efficient spin-photon interfaces such as optical resonators. Here, we demonstrate such NV-nanocavity systems with optical quality factors approaching 10,000 and electron spin coherence times exceeding 200 $\\mu$s using a silicon hard-mask fabrication process. This spin-photon interface is integrated with on-chip microwave striplines for coherent spin control, providing an efficient quantum memory for quantum networks.
Spin Dynamics of Electrons Confined in Silicon Heterostructures
Jock, Ryan Michael
The spin states of electrons confined in silicon heterostructures have shown promise as qubits for quantum information processing. Recently, a host of single and few electron silicon quantum dot device architectures have arisen as implementations for quantum computation. These devices often combine regions of low density two-dimensional (2D) electrons, localized electrons, and interfaces depleted of electrons. Electron spin resonance (ESR) is a unique tool for probing the spin dynamics of both mobile and localized electrons at silicon heterointerfaces and investigating the effects limiting the ability to control electrons and their spin states in these structures. We use a continuous wave ESR method to examine localized 2D electron band-tail states at Si/SiO 2 interfaces in large area metal-oxide-semiconductor transistors. We compare two devices, fabricated in different laboratories, which display similar low temperature (4.2 K) peak mobilities. We find that one of the devices displays a smaller band-tail density of confined states and a shallower characteristic confinement. Thus, ESR reveals a difference in device quality, which is not apparent from mobility measurements, and is a valuable tool for evaluating the interface quality in Si/SiO2 heterostructures. Additionally, we use pulsed ESR techniques to study the spin dynamics of electrons confined in Si/SiGe heterostructures. For mobile 2D electrons, the density-dependent Dyakonov-Perel mechanism dominates spin relaxation. At low 2D densities, stronger electron-electron interactions cause an increase in the electron effective mass, leading to an increase in spin susceptibility. For very low densities, natural disorder localizes electrons at the silicon heterointerface. Naturally localized electrons in these structures display short spin relaxation times (ensembles of around 108 quantum dots in Si/SiGe heterostructures. By tailoring the device structure, a long electron spin relaxation time (T1 = 1.4 ms) is
Long-range spin wave mediated control of defect qubits in nanodiamonds
Andrich, Paolo; de las Casas, Charles F.; Liu, Xiaoying; Bretscher, Hope L.; Berman, Jonson R.; Heremans, F. Joseph; Nealey, Paul F.; Awschalom, David D.
2017-07-17
Hybrid architectures that combine nitrogen-vacancy (NV) centers in diamond with other materials and physical systems have been proposed to enhance the NV center’s capabilities in many quantum sensing and information applications. In particular, spin waves (SWs) in ferromagnetic materials are a promising candidate to implement these platforms due to their strong magnetic fields, which could be used to efficiently interact with the NV centers. Here we develop an yttrium iron garnet-nanodiamond hybrid architecture constructed with the help of directed assembly and transfer printing techniques. Operating at ambient conditions, we demonstrate that surface confined SWs excited in the ferromagnet (FM) can strongly amplify the interactions between a microwave source and the NV centers by enhancing the local microwave magnetic field by several orders of magnitude. Crucially, we show the existence of a regime in which coherent interactions between SWs and NV centers dominate over incoherent mechanisms associated with the broadband magnetic field noise generated by the FM. These accomplishments enable the SW mediated coherent control of spin qubits over distances larger than 200 um, and allow low power operations for future spintronic technologies.
Charge noise and dynamical decoupling in singlet-triplet spin qubits
Ramon, Guy
2013-03-01
We consider theoretically the effects of an ensemble of fluctuating charges on the coherence of a singlet-triplet qubit in gate-defined double quantum dots. We predict a crossover behavior of the system between non-Gaussian noise and 1/f spectrum, going from mesoscopic single-qubit devices to multi-qubit larger devices. With increasing size of the fluctuator ensemble we find a narrowed distribution of qubit dephasing times that result from random sets of fluctuators. At the same time the noise becomes Markovian with a characteristic Gaussian spectrum and it is dominated by a large collection of weakly-coupled fluctuators. The efficiency of dynamical decoupling pulse sequences in restoring coherence is examined as a function of the qubit's working position and the fluctuator ensemble size. Analytical solutions for qubit dephasing in the limits of weak and strong qubit-fluctuator coupling shed light on the distinct dynamics at different parameter regimes. Supported by Research Corporation
Nanofabrication de boites quantiques laterales pour l'optimisation de qubits de spin
Camirand Lemyre, Julien
On présente dans ce travail un nouveau type de qubit de spin dont les performances reposent sur les propriétés d'un seul électron dans une double boîte quantique. Le fort moment dipolaire de la double boite combiné à une large variation du champ magnétique entre les deux boîtes permettrait de réaliser des opérations logiques plus rapidement que dans une seule boîte quantique. Pour maximiser les variations du champ magnétique, on utilisera un micro-aimant placé le plus près possible d'une des deux boîtes. À cette fin, une hétérostructure de GaAs/A1GaAs sur laquelle sont déposées des grilles d'aluminium a été utilisée pour former une double boite quantique latérale. L'occupation par un seul électron de la double boîte est confirmée par des mesures de transport électrique à basse température ainsi que par l'observation du blocage de spin. De plus, un procédé d'oxydation des grilles par plasma d'oxygène a été développé. Une étude des propriétés de l'oxyde formé par cette méthode montre qu'il est possible de placer un micro-aimant directement sur la surface de l'hétérostructure sans affecter l'isolation électrique entre les grilles. Cette nouvelle approche permet de produire des champs magnétiques encore plus intenses que dans les expériences antérieures, pour lesquelles le micro-aimant est placé beaucoup plus loin de la surface. L'ensemble du procédé de fabrication, de la photolithographie à l'électrolithographie, a été développé au cours de ce travail dans les salles blanches du département de génie électrique et dans les salles propres du département de physique de l'Université de Sherbrooke. Ce travail est une étape importante dans la réalisation de qubits de spin plus performants dans les boîtes quantiques latérales. Mots-clés: Information quantique, Spin, Rotations ultra-rapides, Boîtes quantiques latérales, Micro-aimants, Oxydation plasma, Nanofabrication.
Optical manipulation of the Berry phase in a solid-state spin qubit
Yale, Christopher G.; Heremans, F. Joseph; Zhou, Brian B.; Auer, Adrian; Burkard, Guido; Awschalom, David D.
2016-03-01
Phase relations between quantum states represent a resource for storing and processing quantum information. Although quantum phases are commonly controlled dynamically by tuning energetic interactions, the use of geometric phases that accumulate during cyclic evolution may offer superior robustness to noise. To date, demonstrations of geometric phase in solid-state systems employ microwave fields that have limited spatial resolution. Here, we demonstrate an all-optical method to accumulate a geometric phase, the Berry phase, in an individual nitrogen-vacancy centre in diamond. Using stimulated Raman adiabatic passage controlled by diffraction-limited laser light, we loop the nitrogen-vacancy centre's spin around the Bloch sphere to enclose an arbitrary Berry phase. We investigate the limits of this control due to the loss of adiabaticity and decoherence, as well as its robustness to noise introduced into the experimental control parameters. These techniques set the foundation for optical geometric manipulation in photonic networks of solid-state qubits linked and controlled by light.
Nag, Tanay
2016-06-01
We take a central spin model (CSM), consisting of a one-dimensional environmental Ising spin chain and a single qubit connected globally to all the spins of the environment, to study the excess energy (EE) of the environment and the logarithm of decoherence factor namely, generalized fidelity susceptibility per site (GFSS), associated with the qubit under a periodic driving of the transverse field term of environment across its critical point using the Floquet theory. The coupling to the qubit, prepared in a pure state, with the transverse field of the spin chain yields two sets of EE corresponding to the two species of Floquet operators. In the limit of weak coupling, we derive an approximated expression of GFSS after an infinite number of driving period which can successfully estimate the low- and intermediate-frequency behavior of GFSS obtained numerically with a large number of time periods. Our main focus is to analytically investigate the effect of system-environment coupling strength on the EEs and GFSS and relate the behavior of GFSS to EEs as a function of frequency by plausible analytical arguments. We explicitly show that the low-frequency beatinglike pattern of GFSS is an outcome of two frequencies, causing the oscillations in the two branches of EEs, that are dependent on the coupling strength. In the intermediate frequency regime, dip structure observed in GFSS can be justified by the resonance peaks of EEs at those coupling parameter-dependent frequencies; high-frequency saturation behavior of EEs and GFSS are controlled by the same static Hamiltonian and the associated saturation values are related to the coupling strength.
Coupling of spin and orbital motion of electrons in carbon nanotubes.
Kuemmeth, F; Ilani, S; Ralph, D C; McEuen, P L
2008-03-27
Electrons in atoms possess both spin and orbital degrees of freedom. In non-relativistic quantum mechanics, these are independent, resulting in large degeneracies in atomic spectra. However, relativistic effects couple the spin and orbital motion, leading to the well-known fine structure in their spectra. The electronic states in defect-free carbon nanotubes are widely believed to be four-fold degenerate, owing to independent spin and orbital symmetries, and also to possess electron-hole symmetry. Here we report measurements demonstrating that in clean nanotubes the spin and orbital motion of electrons are coupled, thereby breaking all of these symmetries. This spin-orbit coupling is directly observed as a splitting of the four-fold degeneracy of a single electron in ultra-clean quantum dots. The coupling favours parallel alignment of the orbital and spin magnetic moments for electrons and antiparallel alignment for holes. Our measurements are consistent with recent theories that predict the existence of spin-orbit coupling in curved graphene and describe it as a spin-dependent topological phase in nanotubes. Our findings have important implications for spin-based applications in carbon-based systems, entailing new design principles for the realization of quantum bits (qubits) in nanotubes and providing a mechanism for all-electrical control of spins in nanotubes.
Randomized benchmarking of quantum gates implemented by electron spin resonance
Park, Daniel K.; Feng, Guanru; Rahimi, Robabeh; Baugh, Jonathan; Laflamme, Raymond
2016-06-01
Spin systems controlled and probed by magnetic resonance have been valuable for testing the ideas of quantum control and quantum error correction. This paper introduces an X-band pulsed electron spin resonance spectrometer designed for high-fidelity coherent control of electron spins, including a loop-gap resonator for sub-millimeter sized samples with a control bandwidth ∼40 MHz. Universal control is achieved by a single-sideband upconversion technique with an I-Q modulator and a 1.2 GS/s arbitrary waveform generator. A single qubit randomized benchmarking protocol quantifies the average errors of Clifford gates implemented by simple Gaussian pulses, using a sample of gamma-irradiated quartz. Improvements in unitary gate fidelity are achieved through phase transient correction and hardware optimization. A preparation pulse sequence that selects spin packets in a narrowed distribution of static fields confirms that inhomogeneous dephasing (1 / T2∗) is the dominant source of gate error. The best average fidelity over the Clifford gates obtained here is 99.2 % , which serves as a benchmark to compare with other technologies.
One- and two-qubit logic using silicon-MOS quantum dots
Dzurak, Andrew
Spin qubits in silicon are excellent candidates for scalable quantum information processing due to their long coherence times and the enormous investment in silicon CMOS technology. While our Australian effort in Si QC has largely focused on spin qubits based upon phosphorus dopant atoms implanted in Si, we are also exploring spin qubits based on single electrons confined in SiMOS quantum dots. Such qubits can have long spin lifetimes T1 = 2 s, while electric field tuning of the conduction-band valley splitting removes problems due to spin-valley mixing. In isotopically enriched Si-28 these SiMOS qubits have a control fidelity of 99.6%, consistent with that required for fault-tolerant QC. By gate-voltage tuning the electron g*-factor, the ESR operation frequency can be Stark shifted by >10 MHz, allowing individual addressability of many qubits. Most recently we have coupled two SiMOS qubits to realize a CNOT gate using exchange-based controlled phase (CZ) operations. The speed of the two-qubit CZ-operations is controlled electrically via the detuning energy and over 100 two-qubit gates can be performed within a coherence time of 8 μs. We acknowledge support from the Australian Research Council (CE11E0001017), the US Army Research Office (W911NF-13-1-0024) and the Australian National Fabrication Facility.
Yu, Leo; Natarajan, Chandra M.; Horikiri, Tomoyuki; Langrock, Carsten; Pelc, Jason S.; Tanner, Michael G.; Abe, Eisuke; Maier, Sebastian; Schneider, Christian; Höfling, Sven; Kamp, Martin; Hadfield, Robert H.; Fejer, Martin M.; Yamamoto, Yoshihisa
2015-11-01
Practical quantum communication between remote quantum memories rely on single photons at telecom wavelengths. Although spin-photon entanglement has been demonstrated in atomic and solid-state qubit systems, the produced single photons at short wavelengths and with polarization encoding are not suitable for long-distance communication, because they suffer from high propagation loss and depolarization in optical fibres. Establishing entanglement between remote quantum nodes would further require the photons generated from separate nodes to be indistinguishable. Here, we report the observation of correlations between a quantum-dot spin and a telecom single photon across a 2-km fibre channel based on time-bin encoding and background-free frequency downconversion. The downconverted photon at telecom wavelengths exhibits two-photon interference with another photon from an independent source, achieving a mean wavepacket overlap of greater than 0.89 despite their original wavelength mismatch (900 and 911 nm). The quantum-networking operations that we demonstrate will enable practical communication between solid-state spin qubits across long distances.
Liu, Bo; Xue, Kang; Wang, Gangcheng
2016-12-01
In this paper, we investigate the four-qubit spin-1/2 XXZ Heisenberg chain with Dzyaloshinskii-Moriya interaction by topological basis method, and research the relationship between the topological basis states and the ground states. In order to study the Hamiltonian system beyond XXZ model, we introduce two Temperley-Lieb algebra generators and two other generalized generators. Then we investigate the relationship between topological basis and Heisenberg XXZ model with Dzyaloshinskii-Moriya interaction. The results show that the ground state of this model falls on the topological basis state for anti-ferromagnetic case and gapless phase case.
Electron spin separation without magnetic field.
Pawłowski, J; Szumniak, P; Skubis, A; Bednarek, S
2014-08-27
A nanodevice capable of separating spins of two electrons confined in a quantum dot formed in a gated semiconductor nanowire is proposed. Two electrons confined initially in a single quantum dot in the singlet state are transformed into the system of two electrons confined in two spatially separated quantum dots with opposite spins. In order to separate the electrons' spins we exploit transitions between the singlet and the triplet state, which are induced by resonantly oscillating Rashba spin-orbit coupling strength. The proposed device is all electrically controlled and the electron spin separation can be realized within tens of picoseconds. The results are supported by solving numerically the quasi-one-dimensional time-dependent Schroedinger equation for two electrons, where the electron-electron correlations are taken into account in the exact manner.
Isolated Spin Qubits in SiC with a High-Fidelity Infrared Spin-to-Photon Interface
Christle, David J.; Klimov, Paul V.; de las Casas, Charles F.; Szász, Krisztián; Ivády, Viktor; Jokubavicius, Valdas; Ul Hassan, Jawad; Syväjärvi, Mikael; Koehl, William F.; Ohshima, Takeshi; Son, Nguyen T.; Janzén, Erik; Gali, Ádám; Awschalom, David D.
2017-04-01
The divacancies in SiC are a family of paramagnetic defects that show promise for quantum communication technologies due to their long-lived electron spin coherence and their optical addressability at near-telecom wavelengths. Nonetheless, a high-fidelity spin-photon interface, which is a crucial prerequisite for such technologies, has not yet been demonstrated. Here, we demonstrate that such an interface exists in isolated divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that divacancies in 4H-SiC have minimal undesirable spin mixing, and that the optical linewidths in our current sample are already similar to those of recent remote entanglement demonstrations in other systems. Moreover, we find that 3C-SiC divacancies have a millisecond Hahn-echo spin coherence time, which is among the longest measured in a naturally isotopic solid. The presence of defects with these properties in a commercial semiconductor that can be heteroepitaxially grown as a thin film on Si shows promise for future quantum networks based on SiC defects.
Lin, C C Y; Wu, Y Z; Zhang, W M; Lin, Cyrus C.Y.; Soo, Chopin; Wu, Yin-Zhong; Zhang, Wei-Min
2004-01-01
Using electrostatic gates to control the electron positions, we present a new controlled-NOT gate based on quantum dots. The qubit states are chosen to be the spin states of an excess conductor electron in the quantum dot; and the main ingredients of our scheme are the superpositions of space-time paths of electrons and the effect of Coulomb blockade. All operations are performed only on individual quantum dots and are based on fundamental interactions. Without resorting to spin-spin terms or other assumed interactions, the scheme can be realized with a dedicated circuit and a necessary number of quantum dots. Gate fidelity of the quantum computation is also presented.
Rousseau, E
2006-12-15
An electron on helium presents a quantized energy spectrum. The interaction with the environment is considered sufficiently weak in order to allow the realization of a quantum bit (qubit) by using the first two energy levels. The first stage in the realization of this qubit was to trap and control a single electron. This is carried out thanks to a set of micro-fabricated electrodes defining a well of potential in which the electron is trapped. We are able with such a sample to trap and detect a variables number of electrons varying between one and around twenty. This then allowed us to study the static behaviour of a small number of electrons in a trap. They are supposed to crystallize and form structures called Wigner molecules. Such molecules have not yet been observed yet with electrons above helium. Our results bring circumstantial evidence for of Wigner crystallization. We then sought to characterize the qubit more precisely. We sought to carry out a projective reading (depending on the state of the qubit) and a measurement of the relaxation time. The results were obtained by exciting the electron with an incoherent electric field. A clean measurement of the relaxation time would require a coherent electric field. The conclusion cannot thus be final but it would seem that the relaxation time is shorter than calculated theoretically. That is perhaps due to a measurement of the relaxation between the oscillating states in the trap and not between the states of the qubit. (author)
Xiao, M; Martin, I; Yablonovitch, E; Jiang, H W
2004-07-22
The ability to manipulate and monitor a single-electron spin using electron spin resonance is a long-sought goal. Such control would be invaluable for nanoscopic spin electronics, quantum information processing using individual electron spin qubits and magnetic resonance imaging of single molecules. There have been several examples of magnetic resonance detection of a single-electron spin in solids. Spin resonance of a nitrogen-vacancy defect centre in diamond has been detected optically, and spin precession of a localized electron spin on a surface was detected using scanning tunnelling microscopy. Spins in semiconductors are particularly attractive for study because of their very long decoherence times. Here we demonstrate electrical sensing of the magnetic resonance spin-flips of a single electron paramagnetic spin centre, formed by a defect in the gate oxide of a standard silicon transistor. The spin orientation is converted to electric charge, which we measure as a change in the source/drain channel current. Our set-up may facilitate the direct study of the physics of spin decoherence, and has the practical advantage of being composed of test transistors in a conventional, commercial, silicon integrated circuit. It is well known from the rich literature of magnetic resonance studies that there sometimes exist structural paramagnetic defects near the Si/SiO2 interface. For a small transistor, there might be only one isolated trap state that is within a tunnelling distance of the channel, and that has a charging energy close to the Fermi level.
Entanglement and Metrology with Singlet-Triplet Qubits
Shulman, Michael Dean
Electron spins confined in semiconductor quantum dots are emerging as a promising system to study quantum information science and to perform sensitive metrology. Their weak interaction with the environment leads to long coherence times and robust storage for quantum information, and the intrinsic tunability of semiconductors allows for controllable operations, initialization, and readout of their quantum state. These spin qubits are also promising candidates for the building block for a scalable quantum information processor due to their prospects for scalability and miniaturization. However, several obstacles limit the performance of quantum information experiments in these systems. For example, the weak coupling to the environment makes inter-qubit operations challenging, and a fluctuating nuclear magnetic field limits the performance of single-qubit operations. The focus of this thesis will be several experiments which address some of the outstanding problems in semiconductor spin qubits, in particular, singlet-triplet (S-T0) qubits. We use these qubits to probe both the electric field and magnetic field noise that limit the performance of these qubits. The magnetic noise bath is probed with high bandwidth and precision using novel techniques borrowed from the field of Hamiltonian learning, which are effective due to the rapid control and readout available in S-T 0 qubits. These findings allow us to effectively undo the undesired effects of the fluctuating nuclear magnetic field by tracking them in real-time, and we demonstrate a 30-fold improvement in the coherence time T2*. We probe the voltage noise environment of the qubit using coherent qubit oscillations, which is partially enabled by control of the nuclear magnetic field. We find that the voltage noise bath is frequency-dependent, even at frequencies as high as 1MHz, and it shows surprising and, as of yet, unexplained temperature dependence. We leverage this knowledge of the voltage noise environment, the
Scalable quantum register based on coupled electron spins in a room temperature solid
Neumann, P; Naydenov, B; Beck, J; Rempp, F; Steiner, M; Jacques, V; Balasubramanian, G; Markham, M L; Twitchen, D J; Pezzagna, S; Meijer, J; Twamley, J; Jelezko, F; Wrachtrup, J; 10.1038/nphys1536
2010-01-01
Realization of devices based on quantum laws might lead to building processors that outperform their classical analogues and establishing unconditionally secure communication protocols. Solids do usually present a serious challenge to quantum coherence. However, owing to their spin-free lattice and low spin orbit coupling, carbon materials and particularly diamond are suitable for hosting robust solid state quantum registers. We show that scalable quantum logic elements can be realized by exploring long range magnetic dipolar coupling between individually addressable single electron spins associated with separate color centers in diamond. Strong distance dependence of coupling was used to characterize the separation of single qubits 98 A with unprecedented accuracy (3 A) close to a crystal lattice spacing. Our demonstration of coherent control over both electron spins, conditional dynamics, selective readout as well as switchable interaction, opens the way towards a room temperature solid state scalable quant...
Theory of electron spin echoes in solids
Asadullina, N Y; Asadullin, Y Y
2002-01-01
We propose modified Bloch equations (MBEs) with specific power-dependent relaxation and dispersion parameters characteristic for two-pulse excitation and when the magnetic dipole-dipole interactions in the electron spin system control the dephasing. We discriminate between the 'active' (excited by both pulses) and 'passive' (excited by the second pulse only) spins: it is shown that the 'active' spins participate in a new effect, an active spin frequency modulation effect giving rise to the power-dependent dispersion and multiple electron spin echoes (ESEs); the 'passive' spins contribute to the power-dependent relaxation. The MBEs are solved and a general expression for the two-pulse ESEs is obtained. Detailed numerical analysis of this expression gives results in good quantitative agreement with the recent experiments on the two-pulse ESEs at conventional low applied fields. The developed theory is applied also to high field ESEs, which are promising for future investigations. On the basis of published resul...
Gate fidelity and coherence of an electron spin in an Si/SiGe quantum dot with micromagnet.
Kawakami, Erika; Jullien, Thibaut; Scarlino, Pasquale; Ward, Daniel R; Savage, Donald E; Lagally, Max G; Dobrovitski, Viatcheslav V; Friesen, Mark; Coppersmith, Susan N; Eriksson, Mark A; Vandersypen, Lieven M K
2016-10-18
The gate fidelity and the coherence time of a quantum bit (qubit) are important benchmarks for quantum computation. We construct a qubit using a single electron spin in an Si/SiGe quantum dot and control it electrically via an artificial spin-orbit field from a micromagnet. We measure an average single-qubit gate fidelity of ∼99% using randomized benchmarking, which is consistent with dephasing from the slowly evolving nuclear spins in the substrate. The coherence time measured using dynamical decoupling extends up to ∼400 μs for 128 decoupling pulses, with no sign of saturation. We find evidence that the coherence time is limited by noise in the 10-kHz to 1-MHz range, possibly because charge noise affects the spin via the micromagnet gradient. This work shows that an electron spin in an Si/SiGe quantum dot is a good candidate for quantum information processing as well as for a quantum memory, even without isotopic purification.
Schaibley, J R; Burgers, A P; McCracken, G A; Duan, L-M; Berman, P R; Steel, D G; Bracker, A S; Gammon, D; Sham, L J
2013-04-19
The electron spin state of a singly charged semiconductor quantum dot has been shown to form a suitable single qubit for quantum computing architectures with fast gate times. A key challenge in realizing a useful quantum dot quantum computing architecture lies in demonstrating the ability to scale the system to many qubits. In this Letter, we report an all optical experimental demonstration of quantum entanglement between a single electron spin confined to a single charged semiconductor quantum dot and the polarization state of a photon spontaneously emitted from the quantum dot's excited state. We obtain a lower bound on the fidelity of entanglement of 0.59±0.04, which is 84% of the maximum achievable given the timing resolution of available single photon detectors. In future applications, such as measurement-based spin-spin entanglement which does not require sub-nanosecond timing resolution, we estimate that this system would enable near ideal performance. The inferred (usable) entanglement generation rate is 3×10(3) s(-1). This spin-photon entanglement is the first step to a scalable quantum dot quantum computing architecture relying on photon (flying) qubits to mediate entanglement between distant nodes of a quantum dot network.
Quantum Computing with an Electron Spin Ensemble
Wesenberg, Janus; Ardavan, A.; Briggs, G.A.D.
2009-01-01
We propose to encode a register of quantum bits in different collective electron spin wave excitations in a solid medium. Coupling to spins is enabled by locating them in the vicinity of a superconducting transmission line cavity, and making use of their strong collective coupling to the quantized...
Theoretical foundations of electron spin resonance
Harriman, John E
2013-01-01
Theoretical Foundations of Electron Spin Resonance deals with the theoretical approach to electron paramagnetic resonance. The book discusses electron spin resonance in applications related to polyatomic, probably organic, free radicals in condensed phases. The book also focuses on essentially static phenomena, that is, the description and determination of stationary-state energy levels. The author reviews the Dirac theory of the electron in which a four-component wave function is responsible for the behavior of the electron. The author then connects this theory with the nonrelativistic wave f
Shimo-Oka, T.; Miwa, S.; Suzuki, Y.; Mizuochi, N., E-mail: mizuochi@mp.es.osaka-u.ac.jp [Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531 (Japan); Kato, H.; Yamasaki, S. [Energy Technology Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Jelezko, F. [Institut für Quantenoptik, Universität Ulm, Albert-Einstein-Allee 11, 89081 Ulm (Germany)
2015-04-13
Individual nuclear spins in diamond can be optically detected through hyperfine couplings with the electron spin of a single nitrogen-vacancy (NV) center; such nuclear spins have outstandingly long coherence times. Among the hyperfine couplings in the NV center, the nearest neighbor {sup 13}C nuclear spins have the largest coupling strength. Nearest neighbor {sup 13}C nuclear spins have the potential to perform fastest gate operations, providing highest fidelity in quantum computing. Herein, we report on the control of coherences in the NV center where all three nearest neighbor carbons are of the {sup 13}C isotope. Coherence among the three and four qubits are generated and analyzed at room temperature.
Spin Decomposition of Electron in QED
Ji, Xiangdong; Yuan, Feng; Zhang, Jian-Hui; Zhao, Yong
2015-01-01
We perform a systematic study on the spin decomposition of an electron in QED at one-loop order. It is found that the electron orbital angular momentum defined in Jaffe-Manohar and Ji spin sum rules agrees with each other, and the so-called potential angular momentum vanishes at this order. The calculations are performed in both dimensional regularization and Pauli-Villars regularization for the ultraviolet divergences, and they lead to consistent results. We further investigate the calculations in terms of light-front wave functions, and find a missing contribution from the instantaneous interaction in light-front quantization. This clarifies the confusing issues raised recently in the literature on the spin decomposition of an electron, and will help to consolidate the spin physics program for nucleons in QCD.
Yang, A; Steger, M; Sekiguchi, T; Thewalt, M L W; Ladd, T D; Itoh, K M; Riemann, H; Abrosimov, N V; Becker, P; Pohl, H-J
2009-06-26
We demonstrate a method which can hyperpolarize both the electron and nuclear spins of 31P donors in Si at low field, where both would be essentially unpolarized in equilibrium. It is based on the selective ionization of donors in a specific hyperfine state by optically pumping donor bound exciton hyperfine transitions, which can be spectrally resolved in 28Si. Electron and nuclear polarizations of 90% and 76%, respectively, are obtained in less than a second, providing an initialization mechanism for qubits based on these spins, and enabling further ESR and NMR studies on dilute 31P in 28Si.
Bonora, Marco; Becker, James; Saxena, Sunil
2004-10-01
We show the use of the observer blind spots effect for the elimination of electron spin-echo envelope modulation (ESEEM) peaks in double quantum coherence (DQC) electron spin resonance (ESR). The suppression of ESEEM facilitates the routine and unambiguous extraction of distances from DQC-ESR spectra. This is also the first demonstration of this challenging methodology on commercial instrumentation.
Effects of impurity on the entanglement of the three-qubit Heisenberg XXX spin chain
2007-01-01
We investigate the entanglement of the three-qubit Heisenberg XXX chain in the presence of impurity and obtain the analytical expressions of the concurrence C. It is found that for impurity entanglement, C appears only when J1 > J for J > 0, and J1 > 0 for J < 0, and in these two regions C increases with the increase of J1, so is the critical temperature Tc. When J1 >>|J| , C reaches its maximum value 0.5 and Tc reaches the asymptotic value Tc = 3.41448J1. For entanglement between the normal lattices, C appears only when J > 0 and 2J < J1 < J, and initially increases with the increase of J1 and arrives at the maximum value Cmax = (e4JIT-3)/(e4JIT+3) before it decays to zero gradually, so is the critical temperature Tc with, however, the maximum value Tcmax = 4J/ln3.
A modular design of molecular qubits to implement universal quantum gates
Ferrando-Soria, Jesús; Moreno Pineda, Eufemio; Chiesa, Alessandro; Fernandez, Antonio; Magee, Samantha A.; Carretta, Stefano; Santini, Paolo; Vitorica-Yrezabal, Iñigo J.; Tuna, Floriana; Timco, Grigore A.; McInnes, Eric J. L.; Winpenny, Richard E. P.
2016-04-01
The physical implementation of quantum information processing relies on individual modules--qubits--and operations that modify such modules either individually or in groups--quantum gates. Two examples of gates that entangle pairs of qubits are the controlled NOT-gate (CNOT) gate, which flips the state of one qubit depending on the state of another, and the gate that brings a two-qubit product state into a superposition involving partially swapping the qubit states. Here we show that through supramolecular chemistry a single simple module, molecular {Cr7Ni} rings, which act as the qubits, can be assembled into structures suitable for either the CNOT or gate by choice of linker, and we characterize these structures by electron spin resonance spectroscopy. We introduce two schemes for implementing such gates with these supramolecular assemblies and perform detailed simulations, based on the measured parameters including decoherence, to demonstrate how the gates would operate.
Strain and electric field control of hyperfine interactions for donor spin qubits in silicon
Usman, M.; Hill, C. D.; Rahman, R.; Klimeck, G.; Simmons, M. Y.; Rogge, S.; Hollenberg, L. C. L.
2015-06-01
Control of hyperfine interactions is a fundamental requirement for quantum computing architecture schemes based on shallow donors in silicon. However, at present, there is lacking an atomistic approach including critical effects of central-cell corrections and nonstatic screening of the donor potential capable of describing the hyperfine interaction in the presence of both strain and electric fields in realistically sized devices. We establish and apply a theoretical framework, based on atomistic tight-binding theory, to quantitatively determine the strain and electric-field-dependent hyperfine couplings of donors. Our method is scalable to millions of atoms, and yet captures the strain effects with an accuracy level of DFT method. Excellent agreement with the available experimental data sets allow reliable investigation of the design space of multiqubit architectures, based on both strain only as well as hybrid (strain + field) control of qubits. The benefits of strain are uncovered by demonstrating that a hybrid control of qubits based on (001) compressive strain and in-plane (100 or 010) fields results in higher gate fidelities and or faster gate operations, for all of the four donor species considered (P, As, Sb, and Bi). The comparison between different donor species in strained environments further highlights the trends of hyperfine shifts, providing predictions where no experimental data exists. While faster gate operations are realizable with in-plane fields for P, As, and Sb donors, only for the Bi donor, our calculations predict faster gate response in the presence of both in-plane and out-of-plane fields, truly benefiting from the proposed planar field control mechanism of the hyperfine interactions.
Spin dependent electron transport in nanostructures
Yanik, Ahmet Ali
2007-12-01
Spin-electronic devices, exploiting the spin degree of freedom of the current carrying particles, are currently a topic of great interest. In parallel with experimental developments, theoretical studies in this field have been mainly focused on the coherent transport regime characteristics of these devices. However, spin dephasing processes are still a fundamental concern [1-6]. The Landauer transmission formalism has been the widely used method in the coherent transport regime [7]. Recently this formalism has been adapted to incorporate spin scattering processes by introducing random disorder directly into the conducting medium and subsequently solving the disordered transport problem over a large ensemble of disorder distributions [8-10]. Although proposed to be a way of incorporating spin scattering processes, what this approach basically offers is an averaged way of adding random coherent scatterings (similar to the scatterings from boundaries) into the transport problem. Certainly such a treatment of spin-dephasing processes misses the incoherent and inelastic nature of the scattering processes. As a result, a rigorous way of treating the spin scattering processes is still needed [10-12]. The objective of this thesis is to present a quantum transport model based on non-equilibrium Green's function (NEGF) formalism providing a unified approach to incorporate spin scattering processes using generalized interaction Hamiltonians. Here, the NEGF formalism is presented for both coherent and incoherent transport regimes without going into derivational details. Subsequently, spin scattering operators are derived for the specific case of electron-impurity exchange interactions and the model is applied to clarify the experimental measurements [5]. Device characteristics of magnetic tunnel junctions (MTJs) with embedded magnetic impurity layers are studied as a function of tunnel junction thicknesses and barrier heights for varying impurity concentrations in comparison
Electron-mediated nuclear-spin interactions between distant nitrogen-vacancy centers.
Bermudez, A; Jelezko, F; Plenio, M B; Retzker, A
2011-10-07
We propose a scheme enabling controlled quantum coherent interactions between separated nitrogen-vacancy centers in diamond in the presence of strong magnetic fluctuations. The proposed scheme couples nuclear qubits employing the magnetic dipole-dipole interaction between the electron spins and, crucially, benefits from the suppression of the effect of environmental magnetic field fluctuations thanks to a strong microwave driving. This scheme provides a basic building block for a full-scale quantum-information processor or quantum simulator based on solid-state technology.
Electron-Mediated Nuclear-Spin Interactions Between Distant NV Centers
Bermudez, A; Plenio, M B; Retzker, A
2011-01-01
We propose a scheme enabling controlled quantum coherent interactions between separated nitrogen-vacancy centers in diamond in the presence of strong magnetic fluctuations. The proposed scheme couples nuclear qubits employing the magnetic dipole-dipole interaction between the electron spins and, crucially, benefits from the suppression of the effect of environmental magnetic field fluctuations thanks to a strong microwave driving. This scheme provides a basic building block for a full-scale quantum information processor or quantum simulator based on solid-state technology.
Fast Optically Driven Spin Qubit Gates in an InAs Quantum Dot
2010-01-01
epitaxy. The sample is placed in a magneto cryostat to enable operating temperatures of approximately 5 K. Optical excitation through 1μm diameter...Reinecke and D. Gammon, “ Optical Spin Initialization and Nondestructive Measurement in a Quantum Dot Molecule ”, Phys. Rev. Lett., 101, 236804 (2008) 12...Theory of Fast Optical Spin Rotation in a Quantum Dot Based on Geometric Phases and Trapped States”, Phys. Rev. Lett., 99, 217401 (2007) 16. Y
Disentanglement of Two Qubits Coupled to an XY Spin Chain at Finite Temperature
NIE Jing; WANG Lin-Cheng; YI Xue-Xi
2009-01-01
The disentanglement evolution of bipartite spin-1/2 system coupled to a common surrounding XY chain in transverse fields at nonzero temperature is studied in this letter. The dynamical process of the entanglement is numerically and anaiytically investigated. We find that thermal effects can enhance disentanglement if the entangled initial state of the central spins does not in the decoherenee free space. The critical phenomenon of quantum phase transitions reflected in the disentanglement can be washed out by the thermal effect eventually.
Long Spin Relaxation and Coherence Times of Electrons In Gated Si/SiGe Quantum Dots
He, Jianhua; Tyryshkin, A. M.; Lyon, S. A.; Lee, C.-H.; Huang, S.-H.; Liu, C. W.
2012-02-01
Single electron spin states in semiconductor quantum dots are promising candidate qubits. We report the measurement of 250 μs relaxation (T1) and coherence (T2) times of electron spins in gated Si/SiGe quantum dots at 350 mK. The experiments used conventional X-band (10 GHz) pulsed electron spin resonance (pESR), on a large area (3.5 x 20 mm^2) dual-gate undoped high mobility Si/SiGe heterostructure sample, which was patterned with 2 x 10^8 quantum dots using e-beam lithography. Dots having 150 nm radii with a 700 nm period are induced in a natural Si quantum well by the gates. The measured T1 and T2 at 350 mK are much longer than those of free 2D electrons, for which we measured T1 to be 10 μs and T2 to be 6.5 μs in this gated sample. The results provide direct proof that the effects of a fluctuating Rashba field have been greatly suppressed by confining the electrons in quantum dots. From 0.35 K to 0.8 K, T1 of the electron spins in the quantum dots shows little temperature dependence, while their T2 decreased to about 150 μs at 0.8 K. The measured 350 mK spin coherence time is 10 times longer than previously reported for any silicon 2D electron-based structures, including electron spins confined in ``natural quantum dots'' formed by potential disorder at the Si/SiO2ootnotetextS. Shankar et al., Phys. Rev. B 82, 195323 (2010) or Si/SiGe interface, where the decoherence appears to be controlled by spin exchange.
Spin fluctuation theory of itinerant electron magnetism
Takahashi, Yoshinori
2013-01-01
This volume shows how collective magnetic excitations determine most of the magnetic properties of itinerant electron magnets. Previous theories were mainly restricted to the Curie-Weiss law temperature dependence of magnetic susceptibilities. Based on the spin amplitude conservation idea including the zero-point fluctuation amplitude, this book shows that the entire temperature and magnetic field dependence of magnetization curves, even in the ground state, is determined by the effect of spin fluctuations. It also shows that the theoretical consequences are largely in agreement with many experimental observations. The readers will therefore gain a new comprehensive perspective of their unified understanding of itinerant electron magnetism.
Theory of electron spin echoes in solids
Asadullina, N.Ya.; Asadullin, T.Ya.; Asadullin, Ya.Ya. [Kazan State Technical University, Department of General Physics, Karl Marx Street 10, Kazan (Russian Federation)
2002-11-04
We propose modified Bloch equations (MBEs) with specific power-dependent relaxation and dispersion parameters characteristic for two-pulse excitation and when the magnetic dipole-dipole interactions in the electron spin system control the dephasing. We discriminate between the 'active' (excited by both pulses) and 'passive' (excited by the second pulse only) spins: it is shown that the 'active' spins participate in a new effect, an active spin frequency modulation effect giving rise to the power-dependent dispersion and multiple electron spin echoes (ESEs); the 'passive' spins contribute to the power-dependent relaxation. The MBEs are solved and a general expression for the two-pulse ESEs is obtained. Detailed numerical analysis of this expression gives results in good quantitative agreement with the recent experiments on the two-pulse ESEs at conventional low applied fields. The developed theory is applied also to high field ESEs, which are promising for future investigations. On the basis of published results it is deduced that the instantaneous diffusion mechanism is ineffective.
Effects of impurity on the entanglement of the three-qubit Heisenberg XXX spin chain
HU MingLiang; TIAN DongPing
2007-01-01
We investigate the entanglement of the three-qubit Heisenberg XXX chain in the presence of impurity and obtain the analytical expressions of the concurrence C. It is found that for impurity entanglement, C appears only when J1 ＞ J for J ＞ 0, and J1 ＞ 0 for J ＜ 0, and in these two regions C increases with the increase of J1, so is the critical temperature Tc. When J1 >> |J|, C reaches its maximum value 0.5 and Tc reaches the asymptotic value Tc = 3.41448J1. For entanglement between the normal lattices, C appears only when J ＞ 0 and -2J ＜ J1 ＜ J, and initially increases with the increase of J1 and arrives at the maximum value Cmax= (e4J/T-3)/(e4J/T+3) before it decays to zero gradually, so is the critical temperature Tc with, however, the maximum value Tcmax = 4J/In3.
High-Fidelity Microwave Control of Single-Atom Spin Qubits in Silicon
2014-07-08
systems, the value of a bit is obtained by measuring a low-voltage (0) or high-voltage (1) at the terminals of a transistor. In order to measure our...time TH2 . In bulk experiments, this measurement is realised by detecting the magnetisation of the spins after the πx pulse. Magnetisation will be...current values for the separate states N↑ and N↓ (see Figure 2.10b). From these we can extract the electrical fidelity in measuring a spin-up (Fe
Undergraduate Electron-Spin-Resonance Experiment.
Willis, James S.
1980-01-01
Describes the basic procedures for use of an electron-spin resonance spectrometer and potassium azide (KN3) in an experiment which extends from the phase of sample preparation (crystal growth, sample mounting, and orientation) through data taking to the stages of calculation and theoretical explanation. (Author/DS)
A. Gover
2006-06-01
Full Text Available The problems of spin-polarized free-electron beam interaction with electromagnetic wave at electron-spin resonance conditions in a magnetic field and of superradiant spin-flip radiative emission are analyzed in the framework of a comprehensive classical model. The spontaneous emission of spin-flip radiation from electron beams is very weak. We show that the detectivity of electron spin resonant spin-flip and combined spin-flip/cyclotron-resonance-emission radiation can be substantially enhanced by operating with ultrashort spin-polarized electron beam bunches under conditions of superradiant (coherent emission. The proposed radiative spin-state modulation and the spin-flip radiative emission schemes can be used for control and noninvasive diagnostics of polarized electron/positron beams. Such schemes are of relevance in important scattering experiments off nucleons in nuclear physics and off magnetic targets in condensed matter physics.
Electron Spin in Single Wall Carbon Nanotubes
Lindelof, P. E.; Borggreen, J.; Jensen, A.; Nygård, J.; Poulsen, P. R.
2003-10-01
We review aspects of electrical transport in metallic single wall carbon nanotubes (SWCNT) related to the spin of the conductance electrons. For large contact resistances, R ≫ h/2e2, a SWCNT exhibits Coulomb blockade, and transmission can only occur, when a gate voltage leads to an energy degeneracy for two different numbers of electrons in the SWCNT. The Coulomb blockade gate voltage change is directly proportional to the addition energy for single electron tunnelling. In certain ideal cases every second of the populated electronic states has a higher addition energy, indicating that two spindegenerate electrons are roomed at each orbital state. A low addition energy therefore corresponds to approaching an even number of electrons. The odd-even alternation can be checked in a magnetic field, since then the odd additional electron may enter in one of two Zeeman states. If the high resistance contact is a tunnel junction, the transmission reflects the density of states. This leads to a direct detection of the so-called Luttinger liquid state of the electrons. Ferromagnetic contacts to the SWCNT leads to a conductance which depends on the orientation of the magnetic domains in the contacts. The magnetoresistance effect can be much larger than expected from a simple spin-valve phenomenon. For any intermediate normal metal (Au) contact resistances, R ˜ h/2e2, the Coulomb blockade may still separate the single electron states in the SWCNT with odd and even numbers of electrons. However, at the lowest temperatures the transmission only shows Coulomb blockade for even number of electrons. In the situations with odd number of electrons a coherent tunnelling process dominates. This shortage of the blockade is rooted in the Kondo states formed in the two Au electrodes by exchange interaction due to the spin state in the SWCNT. This tunnelling process is a result of a net spin on the SWCNT and consequently a spin degeneracy. A triplet state is forced into degeneracy with
Ishmuratov, I. K.; Baibekov, E. I.
2016-12-01
We investigate the possibility to restore transient nutations of electron spin centers embedded in the solid using specific composite pulse sequences developed previously for the application in nuclear magnetic resonance spectroscopy. We treat two types of systematic errors simultaneously: (i) rotation angle errors related to the spatial distribution of microwave field amplitude in the sample volume, and (ii) off-resonance errors related to the spectral distribution of Larmor precession frequencies of the electron spin centers. Our direct simulations of the transient signal in erbium- and chromium-doped CaWO4 crystal samples with and without error corrections show that the application of the selected composite pulse sequences can substantially increase the lifetime of Rabi oscillations. Finally, we discuss the applicability limitations of the studied pulse sequences for the use in solid-state electron paramagnetic resonance spectroscopy.
Quantum Computation and Spin Electronics
DiVincenzo, David P.; Burkard, Guido; Loss, Daniel; Sukhorukov, Eugene V.
1999-01-01
In this chapter we explore the connection between mesoscopic physics and quantum computing. After giving a bibliography providing a general introduction to the subject of quantum information processing, we review the various approaches that are being considered for the experimental implementation of quantum computing and quantum communication in atomic physics, quantum optics, nuclear magnetic resonance, superconductivity, and, especially, normal-electron solid state physics. We discuss five ...
Entangling distant resonant exchange qubits via circuit quantum electrodynamics
Srinivasa, V.; Taylor, J. M.; Tahan, Charles
2016-11-01
We investigate a hybrid quantum system consisting of spatially separated resonant exchange qubits, defined in three-electron semiconductor triple quantum dots, that are coupled via a superconducting transmission line resonator. Drawing on methods from circuit quantum electrodynamics and Hartmann-Hahn double resonance techniques, we analyze three specific approaches for implementing resonator-mediated two-qubit entangling gates in both dispersive and resonant regimes of interaction. We calculate entangling gate fidelities as well as the rate of relaxation via phonons for resonant exchange qubits in silicon triple dots and show that such an implementation is particularly well suited to achieving the strong coupling regime. Our approach combines the favorable coherence properties of encoded spin qubits in silicon with the rapid and robust long-range entanglement provided by circuit QED systems.
Schwartz, I; Schmidgall, E R; Gantz, L; Don, Y; Zielinski, M; Gershoni, D
2015-01-01
We use one single, few-picosecond-long, variably polarized laser pulse to deterministically write any selected spin state of a quantum dot confined dark exciton whose life and coherence time are six and five orders of magnitude longer than the laser pulse duration, respectively. The pulse is tuned to an absorption resonance of an excited dark exciton state, which acquires non-negligible oscillator strength due to residual mixing with bright exciton states. We obtain a high fidelity one-to-one mapping from any point on the Poincar\\'e sphere of the pulse polarization to a corresponding point on the Bloch sphere of the spin of the deterministically photogenerated dark exciton.
2016-09-01
10 16. Gain plot of DARPA SURF tunable band-pass filter tuned to 950-MHz .............................. 10 v 17. VSG at -50 dBm: Experimental... strength and the pulse duration with enough accuracy to control the spin states reliably. A rotation angle error arises from the inaccuracy of the pulse...gain. Figure 8 plots the simulation in red and a direct output from the VSG in blue. The VSG alone provides a high-quality pulse train with a 15-MHz
Janzing, D; Beth, T; Janzing, Dominik; Decker, Thomas; Beth, Thomas
2003-01-01
An n-qubit quantum register can in principle be completely controlled by operating on a single qubit that interacts with the register via an appropriate fixed interaction. We consider a hypothetical system consisting of n spin-1/2 nuclei that interact with an electron spin via a magnetic interaction. We describe algorithms that measure non-trivial joint observables on the register by acting on the control spin only. For large n this is not an efficient model for universal quantum computation but it can be modified to an efficient one if one allows n possible positions of the control particle. This toy model of measurements illustrates in which way specific interactions between the register and a probe particle support specific types of joint measurements in the sense that some joint observables can be measured by simple sequences of operations on the probe particle.
Doppler effect induced spin relaxation boom
Zhao, Xinyu; Huang, Peihao; Hu, Xuedong
2016-03-01
We study an electron spin qubit confined in a moving quantum dot (QD), with our attention on both spin relaxation, and the product of spin relaxation, the emitted phonons. We find that Doppler effect leads to several interesting phenomena. In particular, spin relaxation rate peaks when the QD motion is in the transonic regime, which we term a spin relaxation boom in analogy to the classical sonic boom. This peak indicates that a moving spin qubit may have even lower relaxation rate than a static qubit, pointing at the possibility of coherence-preserving transport for a spin qubit. We also find that the emitted phonons become strongly directional and narrow in their frequency range as the qubit reaches the supersonic regime, similar to Cherenkov radiation. In other words, fast moving excited spin qubits can act as a source of non-classical phonons. Compared to classical Cherenkov radiation, we show that quantum dot confinement produces a small but important correction on the Cherenkov angle. Taking together, these results have important implications to both spin-based quantum information processing and coherent phonon dynamics in semiconductor nanostructures.
Towards optimizing two-qubit operations in three-electron double quantum dots
Frees, Adam; Gamble, John King; Mehl, Sebastian; Friesen, Mark; Coppersmith, S. N.
The successful implementation of single-qubit gates in the quantum dot hybrid qubit motivates our interest in developing a high fidelity two-qubit gate protocol. Recently, extensive work has been done to characterize the theoretical limitations and advantages in performing two-qubit operations at an operation point located in the charge transition region. Additionally, there is evidence to support that single-qubit gate fidelities improve while operating in the so-called ``far-detuned'' region, away from the charge transition. Here we explore the possibility of performing two-qubit gates in this region, considering the challenges and the benefits that may present themselves while implementing such an operational paradigm. This work was supported in part by ARO (W911NF-12-0607) (W911NF-12-R-0012), NSF (PHY-1104660), ONR (N00014-15-1-0029). The authors gratefully acknowledge support from the Sandia National Laboratories Truman Fellowship Program, which is funded by the Laboratory Directed Research and Development (LDRD) Program. Sandia is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the US Department of Energy's National Nuclear Security Administration under Contract No. DE-AC04-94AL85000.
Magnetic resonance spectroscopy of an atomically thin material using a single-spin qubit
Lovchinsky, I.; Sanchez-Yamagishi, J. D.; Urbach, E. K.; Choi, S.; Fang, S.; Andersen, T. I.; Watanabe, K.; Taniguchi, T.; Bylinskii, A.; Kaxiras, E.; Kim, P.; Park, H.; Lukin, M. D.
2017-02-01
Two-dimensional (2D) materials offer a promising platform for exploring condensed matter phenomena and developing technological applications. However, the reduction of material dimensions to the atomic scale poses a challenge for traditional measurement and interfacing techniques that typically couple to macroscopic observables. We demonstrate a method for probing the properties of 2D materials via nanometer-scale nuclear quadrupole resonance (NQR) spectroscopy using individual atomlike impurities in diamond. Coherent manipulation of shallow nitrogen-vacancy (NV) color centers enables the probing of nanoscale ensembles down to approximately 30 nuclear spins in atomically thin hexagonal boron nitride (h-BN). The characterization of low-dimensional nanoscale materials could enable the development of new quantum hybrid systems, combining atomlike systems coherently coupled with individual atoms in 2D materials.
Bonizzoni, C; Ghirri, A; Bader, K; van Slageren, J; Perfetti, M; Sorace, L; Lan, Y; Fuhr, O; Ruben, M; Affronte, M
2016-11-14
We present spectroscopic measurements looking for the coherent coupling between molecular magnetic centers and microwave photons. The aim is to find the optimal conditions and the best molecular features to achieve the quantum strong coupling regime, for which coherent dynamics of hybrid photon-spin states take place. To this end, we used a high critical temperature YBCO superconducting planar resonator working at 7.7 GHz and at low temperatures to investigate three molecular mononuclear coordination compounds, namely (PPh4)2[Cu(mnt)2] (where mnt(2-) = maleonitriledithiolate), [ErPc2](-)TBA(+) (where pc(2-) is the phtalocyaninato and TBA(+) is the tetra-n-butylammonium cation) and Dy(trensal) (where H3trensal = 2,2',2''-tris(salicylideneimino)triethylamine). Although the strong coupling regime was not achieved in these preliminary experiments, the results provided several hints on how to design molecular magnetic centers to be integrated into hybrid quantum circuits.
Optical manipulation of Berry phase in a solid-state spin qubit
Yale, Christopher G; Zhou, Brian B; Auer, Adrian; Burkard, Guido; Awschalom, David D
2015-01-01
The phase relation between quantum states represents an essential resource for the storage and processing of quantum information. While quantum phases are commonly controlled dynamically by tuning energetic interactions, utilizing geometric phases that accumulate during cyclic evolution may offer superior robustness to noise. To date, demonstrations of geometric phase control in solid-state systems rely on microwave fields that have limited spatial resolution. Here, we demonstrate an all-optical method based on stimulated Raman adiabatic passage to accumulate a geometric phase, the Berry phase, in an individual nitrogen-vacancy (NV) center in diamond. Using diffraction-limited laser light, we guide the NV center's spin along loops on the Bloch sphere to enclose arbitrary Berry phase and characterize these trajectories through time-resolved state tomography. We investigate the limits of this control due to loss of adiabiaticity and decoherence, as well as its robustness to noise intentionally introduced into t...
Electron-Spin Resonance in Boron Carbide
Wood, Charles; Venturini, Eugene L.; Azevedo, Larry J.; Emin, David
1987-01-01
Samples exhibit Curie-law behavior in temperature range of 2 to 100 K. Technical paper presents studies of electron-spin resonance of samples of hot pressed B9 C, B15 C2, B13 C2, and B4 C. Boron carbide ceramics are refractory solids with high melting temperatures, low thermal conductives, and extreme hardnesses. They show promise as semiconductors at high temperatures and have unusually large figures of merit for use in thermoelectric generators.
Electron Doping a Kagome Spin Liquid
Kelly, Z. A.; Gallagher, M. J.; McQueen, T. M.
2016-10-01
Herbertsmithite, ZnCu3 (OH )6Cl2 , is a two-dimensional kagome lattice realization of a spin liquid, with evidence for fractionalized excitations and a gapped ground state. Such a quantum spin liquid has been proposed to underlie high-temperature superconductivity and is predicted to produce a wealth of new states, including a Dirac metal at 1 /3 electron doping. Here, we report the topochemical synthesis of electron-doped ZnLix Cu3 (OH )6Cl2 from x =0 to x =1.8 (3 /5 per Cu2 + ). Contrary to expectations, no metallicity or superconductivity is induced. Instead, we find a systematic suppression of magnetic behavior across the phase diagram. Our results demonstrate that significant theoretical work is needed to understand and predict the role of doping in magnetically frustrated narrow band insulators, particularly the interplay between local structural disorder and tendency toward electron localization, and pave the way for future studies of doped spin liquids.
Observation of coherent oscillations in a single electron spin.
Jelezko, F; Gaebel, T; Popa, I; Gruber, A; Wrachtrup, J
2004-02-20
Rabi nutations and Hahn echo modulation of a single electron spin in a single defect center have been observed. The coherent evolution of the spin quantum state is followed via optical detection of the spin state. Coherence times up to several microseconds at room temperature have been measured. Optical excitation of the spin states leads to decoherence. Quantum beats between electron spin transitions in a single spin Hahn echo experiment are observed. A closer analysis reveals that beats also result from the hyperfine coupling of the electron spin to a single 14N nuclear spin. The results are analyzed in terms of a density matrix approach of an electron spin interacting with two oscillating fields.
Spin current and polarization in impure two-dimensional electron systems with spin-orbit coupling.
Mishchenko, E G; Shytov, A V; Halperin, B I
2004-11-26
We derive the transport equations for two-dimensional electron systems with Rashba spin-orbit interaction and short-range spin-independent disorder. In the limit of slow spatial variations, we obtain coupled diffusion equations for the electron density and spin. Using these equations we calculate electric-field induced spin accumulation and spin current in a finite-size sample for an arbitrary ratio between spin-orbit energy splitting Delta and elastic scattering rate tau(-1). We demonstrate that the spin-Hall conductivity vanishes in an infinite system independent of this ratio.
From spin flip excitations to the spin susceptibility enhancement of a two-dimensional electron gas.
Perez, F; Aku-leh, C; Richards, D; Jusserand, B; Smith, L C; Wolverson, D; Karczewski, G
2007-07-13
The g-factor enhancement of the spin-polarized two-dimensional electron gas was measured directly over a wide range of spin polarizations, using spin flip resonant Raman scattering spectroscopy on two-dimensional electron gases embedded in Cd(1-x)Mn(x)Te semimagnetic quantum wells. At zero Raman transferred momentum, the single-particle spin flip excitation, energy Z*, coexists in the Raman spectrum with the spin flip wave of energy Z, the bare giant Zeeman splitting. We compare the measured g-factor enhancement with recent spin-susceptibility enhancement theories and deduce the spin-polarization dependence of the mass renormalization.
Coherent manipulation of an NV center and one carbon nuclear spin
Scharfenberger, Burkhard; Nemoto, Kae [National Institute of Informatics, 2-1-2 Hitotsubashi, Chiyoda-ku, Tokyo 101-8430 (Japan); Munro, William J. [NTT Basic Research Laboratories, NTT Corporation, 3-1 Morinosato Wakamiya, Atsugi, Kanagawa 243-0198 (Japan)
2014-12-04
We study a three-qubit system formed by the NV center’s electronic and nuclear spin plus an adjacent spin 1/2 carbon {sup 13}C. Specifically, we propose a manipulation scheme utilizing the hyperfine coupling of the effective S=1 degree of freedom of the vacancy electrons to the two adjacent nuclear spins to achieve accurate coherent control of all three qubits.
Coherent control and suppressed nuclear feedback of a single quantum dot hole qubit
De Greve, Kristiaan; Press, David; Ladd, Thaddeus D; Bisping, Dirk; Schneider, Christian; Kamp, Martin; Worschech, Lukas; Hoefling, Sven; Forchel, Alfred; Yamamoto, Yoshihisa
2011-01-01
Future communication and computation technologies that exploit quantum information require robust and well-isolated qubits. Electron spins in III-V semiconductor quantum dots, while promising candidates, see their dynamics limited by undesirable hysteresis and decohering effects of the nuclear spin bath. Replacing electrons with holes should suppress the hyperfine interaction and consequently eliminate strong nuclear effects. Using picosecond optical pulses, we demonstrate coherent control of a single hole qubit and examine both free-induction and spin-echo decay. In moving from electrons to holes, we observe significantly reduced hyperfine interactions, evidenced by the reemergence of hysteresis-free dynamics, while obtaining similar coherence times, limited by non-nuclear mechanisms. These results demonstrate the potential of optically controlled, quantum dot hole qubits.
Electron spin coherence and effect of spin polarization on electron relaxation dynamics in GaAs
Teng, Lihua; Wang, Xia; Ge, Weikun; Lai, Tianshu
2011-09-01
Time-resolved circularly and linearly polarized pump-probe spectroscopy is used to study the evolution of the electron spin coherence and electron relaxation dynamics in bulk GaAs at 9.6 K. In particular, their dependence on photon energy (or electron excess energy) is carefully investigated. The absorption quantum beats which are observed in circularly polarized pump-probe spectroscopy are obtained, reflecting the dephasing of the electron spin coherence. A circularly dichromatic pump-probe model is developed with both the spin-polarization-dependent band-filling and band-gap renormalization effects being taken into account. The model is used to simulate the differential transmission spectra for the collinearly polarized, co-helicity circularly polarized and cross-helicity circularly polarized pump-probe configurations, respectively. It is found that the model simulates well the features of the absorption quantum beats for a spin-dependent thermalized distribution of the photocreated carriers by a circularly polarized pump pulse, such as the variation of the oscillatory amplitude and phase reversal of the absorption quantum beats with photon energy increase. The simulation is in good agreement with our experimental results and reveals the effect of spin polarization on electron relaxation dynamics.
Evolution of electron spin polarization in semiconductor heterostructures
Pershin, Yuriy; Privman, Vladimir
2004-03-01
Last years theoretical and experimental investigations of electron spin-related effects in semiconductor heterostructures have received much consideration because of idea to create a semiconductor device based on the manipulation of electron spin. High degree of electron spin polarization is of crucial importance in operation of spintronic devices. We study possibilities to increase electron spin relaxation time by different means in systems where the D'yakonov-Perel' relaxation mechanism is dominant. Specifically, we show that the electron spin relaxation time in a two-dimensional electron gas with an antidote lattice increases exponentially with antidote radius for certain values of parameters. In another approach, we propose to use electron spin polarization having non-homogeneous direction of spin polarization vector in operation of a spintronic device. It is found that that the electron spin relaxation time essentially depends on the initial spin polarization distribution. This effect has its origin in the coherent spin precession of electrons diffusing in the same direction. We predict a long spin relaxation time of a novel structure: a spin coherence standing wave and discuss its experimental realization.
Induction-detection electron spin resonance with spin sensitivity of a few tens of spins
Artzi, Yaron; Twig, Ygal; Blank, Aharon [Schulich Faculty of Chemistry Technion—Israel Institute of Technology, Haifa 32000 (Israel)
2015-02-23
Electron spin resonance (ESR) is a spectroscopic method that addresses electrons in paramagnetic materials directly through their spin properties. ESR has many applications, ranging from semiconductor characterization to structural biology and even quantum computing. Although it is very powerful and informative, ESR traditionally suffers from low sensitivity, requiring many millions of spins to get a measureable signal with commercial systems using the Faraday induction-detection principle. In view of this disadvantage, significant efforts were made recently to develop alternative detection schemes based, for example, on force, optical, or electrical detection of spins, all of which can reach single electron spin sensitivity. This sensitivity, however, comes at the price of limited applicability and usefulness with regard to real scientific and technological issues facing modern ESR which are currently dealt with conventional induction-detection ESR on a daily basis. Here, we present the most sensitive experimental induction-detection ESR setup and results ever recorded that can detect the signal from just a few tens of spins. They were achieved thanks to the development of an ultra-miniature micrometer-sized microwave resonator that was operated at ∼34 GHz at cryogenic temperatures in conjunction with a unique cryogenically cooled low noise amplifier. The test sample used was isotopically enriched phosphorus-doped silicon, which is of significant relevance to spin-based quantum computing. The sensitivity was experimentally verified with the aid of a unique high-resolution ESR imaging approach. These results represent a paradigm shift with respect to the capabilities and possible applications of induction-detection-based ESR spectroscopy and imaging.
Saito, Shiro; Zhu, Xiaobo; Amsüss, Robert; Matsuzaki, Yuichiro; Kakuyanagi, Kosuke; Shimo-Oka, Takaaki; Mizuochi, Norikazu; Nemoto, Kae; Munro, William J; Semba, Kouichi
2013-09-06
We have built a hybrid system composed of a superconducting flux qubit (the processor) and an ensemble of nitrogen-vacancy centers in diamond (the memory) that can be directly coupled to one another, and demonstrated how information can be transferred from the flux qubit to the memory, stored, and subsequently retrieved. We have established the coherence properties of the memory and succeeded in creating an entangled state between the processor and memory, demonstrating how the entangled state's coherence is preserved. Our results are a significant step towards using an electron spin ensemble as a quantum memory for superconducting qubits.
van Bree, J.; Silov, A. Yu.; van Maasakkers, M. L.; Pryor, C. E.; Flatté, M. E.; Koenraad, P. M.
2016-01-01
Using single spins in semiconductor quantum dots as qubits requires full control over the spin state. As the g tensor provides the coupling in a Hamiltonian between a spin and an external magnetic field, a deeper understanding of the g tensor underlies magnetic-field control of the spin. The g tensor is affected by the presence of spin-correlated orbital currents, of which the spatial structure has been recently clarified. Here we extend that framework to investigate the influence of the shape of quantum dots on the anisotropy of the electron g tensor. We find that the spin-correlated orbital currents form a simple current loop perpendicular to the magnetic moment's orientation. The current loop is therefore directly sensitive to the shape of the nanostructure: for cylindrical quantum dots, the electron g -tensor anisotropy is mainly governed by the aspect ratio of the dots. Through a systematic experimental study of the size dependence of the separate electron and hole g tensors of InAs/InP quantum dots, we have validated this picture. Moreover, we find that through size engineering it is possible to independently change the sign of the in-plane and growth direction electron g factors. The hole g tensor is found to be strongly anisotropic and very sensitive to the radius and elongation. The comparable importance of itinerant and localized currents to the hole g tensor complicates the analysis relative to the electron g tensor.
Spin Effects in Collisions of Electrons with Atoms and Molecules
无
2000-01-01
Some recent experimental and theoretical work on spin-dependent electron-atom and electron-molecule collisions is reviewed. The spin is involved in such collisions by explicit spin-dependent interactions such as the spin-orbit interaction of the continuum electron (Mott scattering) but also by exchange, which, in conjunction with the Pauli principle, gives rise to observable spin exchange effects. We present results for Mn and Na atoms and experiments in which electron dichroism with chiral molecules has been studied.
Two-Dimensional Electron-Spin Resonance
Freed, Jack H.
2000-03-01
The extension of the concepts of 2D-NMR to ESR posed significant technological challenges, especially for liquids. ESR relaxation times are very short, as low as 10-15 ns. for T_2's. Spectral bandwidths are 100-250 MHz for nitroxide spin labels. Adequate coverage is obtained with 3-5 ns. π/2 (9-17 GHz) microwave pulses into a small low Q resonator. Dead-times are currently 25-30 ns. Additional requirements are rapid phase shifting for phase cycling, nsec. data acquisition, and fast repetition rates (10-100 kHz). 2D-ELDOR (electron-electron double resonance), which is a 3-pulse 2D-exchange experiment, takes about 30 minutes with just 0.5 nanomole spin-probe in solution (SNR 200). 2D-ELDOR is very useful in studies of molecular dynamics and local structure in complex fluids. For such media, the slow rotational dynamics requires a theory based upon the stochastic Liouville equation which enables quantitative interpretation of 2D-ELDOR experiments. In studies of spin-probes in a liquid crystal new insights could be obtained on the dynamic structure in different phases. One obtains, in addition to ordering and reorientation rates of the probes, details of the local dynamic cage: its orienting potential and (slow) relaxation rate. 2D-ELDOR overcomes the loss of resolution resulting from microscopically ordered but macroscopically disordered complex fluids. This is illustrated by studies of the dynamic structure of lipid membrane vesicles, and the effects of adding a peptide. The short dead times enable the observation of both the bulk lipids and the more immobilized lipids that coat (or are trapped) by the (aggregates of) peptides. Also, new developments of multi-quantum (2D) FT-ESR from nitroxide spin labels interacting by dipolar interactions show considerable promise in measuring distances of ca. 15-70A in macromolecules.
Lee, Seungwon; vonAllmen, Paul; Oyafuso, Fabiano; Klimeck, Gerhard; Whale, K. Birgitta
2004-01-01
Electron spin dephasing and decoherence by its interaction with nuclear spins in self-assembled quantum dots are investigated in the framework of the empirical tight-binding model. Electron spin dephasing in an ensemble of dots is induced by the inhomogeneous precession frequencies of the electron among dots, while electron spin decoherence in a single dot arises from the inhomogeneous precession frequencies of nuclear spins in the dot. For In(x)Ga(1-x) As self-assembled dots containing 30000 nuclei, the dephasing and decoherence times are predicted to be on the order of 100 ps and 1 (micro)s.
Quantum State Transfer from a Single Photon to a Distant Quantum-Dot Electron Spin
He, Yu; He, Yu-Ming; Wei, Yu-Jia; Jiang, Xiao; Chen, Kai; Lu, Chao-Yang; Pan, Jian-Wei; Schneider, Christian; Kamp, Martin; Höfling, Sven
2017-08-01
Quantum state transfer from flying photons to stationary matter qubits is an important element in the realization of quantum networks. Self-assembled semiconductor quantum dots provide a promising solid-state platform hosting both single photon and spin, with an inherent light-matter interface. Here, we develop a method to coherently and actively control the single-photon frequency bins in superposition using electro-optic modulators, and measure the spin-photon entanglement with a fidelity of 0.796 ±0.020 . Further, by Greenberger-Horne-Zeilinger-type state projection on the frequency, path, and polarization degrees of freedom of a single photon, we demonstrate quantum state transfer from a single photon to a single electron spin confined in an InGaAs quantum dot, separated by 5 m. The quantum state mapping from the photon's polarization to the electron's spin is demonstrated along three different axes on the Bloch sphere, with an average fidelity of 78.5%.
Quantum State Transfer from a Single Photon to a Distant Quantum-Dot Electron Spin.
He, Yu; He, Yu-Ming; Wei, Yu-Jia; Jiang, Xiao; Chen, Kai; Lu, Chao-Yang; Pan, Jian-Wei; Schneider, Christian; Kamp, Martin; Höfling, Sven
2017-08-11
Quantum state transfer from flying photons to stationary matter qubits is an important element in the realization of quantum networks. Self-assembled semiconductor quantum dots provide a promising solid-state platform hosting both single photon and spin, with an inherent light-matter interface. Here, we develop a method to coherently and actively control the single-photon frequency bins in superposition using electro-optic modulators, and measure the spin-photon entanglement with a fidelity of 0.796±0.020. Further, by Greenberger-Horne-Zeilinger-type state projection on the frequency, path, and polarization degrees of freedom of a single photon, we demonstrate quantum state transfer from a single photon to a single electron spin confined in an InGaAs quantum dot, separated by 5 m. The quantum state mapping from the photon's polarization to the electron's spin is demonstrated along three different axes on the Bloch sphere, with an average fidelity of 78.5%.
A coherent beam splitter for electronic spin states.
Petta, J R; Lu, H; Gossard, A C
2010-02-05
Rapid coherent control of electron spin states is required for implementation of a spin-based quantum processor. We demonstrated coherent control of electronic spin states in a double quantum dot by sweeping an initially prepared spin-singlet state through a singlet-triplet anticrossing in the energy-level spectrum. The anticrossing serves as a beam splitter for the incoming spin-singlet state. When performed within the spin-dephasing time, consecutive crossings through the beam splitter result in coherent quantum oscillations between the singlet state and a triplet state. The all-electrical method for quantum control relies on electron-nuclear spin coupling and drives single-electron spin rotations on nanosecond time scales.
Spin-to-Orbital Angular Momentum Conversion and Spin-Polarization Filtering in Electron Beams
Karimi, Ebrahim; Grillo, Vincenzo; Santamato, Enrico; 10.1103/PhysRevLett.108.044801
2012-01-01
We propose the design of a space-variant Wien filter for electron beams that induces a spin half-turn and converts the corresponding spin angular momentum variation into orbital angular momentum of the beam itself by exploiting a geometrical phase arising in the spin manipulation. When applied to a spatially coherent input spin-polarized electron beam, such a device can generate an electron vortex beam, carrying orbital angular momentum. When applied to an unpolarized input beam, the proposed device, in combination with a suitable diffraction element, can act as a very effective spin-polarization filter. The same approach can also be applied to neutron or atom beams.
Schuster, D I; Fragner, A; Dykman, M I; Lyon, S A; Schoelkopf, R J
2010-07-23
We propose a hybrid architecture in which an on-chip high finesse superconducting cavity is coupled to the lateral motion and spin state of a single electron trapped on the surface of superfluid helium. We estimate the motional coherence times to exceed 15 μs, while energy will be coherently exchanged with the cavity photons in less than 10 ns for charge states and faster than 1 μs for spin states, making the system attractive for quantum information processing and strong coupling cavity quantum electrodynamics experiments. The cavity is used for nondestructive readout and as a quantum bus mediating interactions between distant electrons or an electron and a superconducting qubit.
High-Fidelity Bidirectional Nuclear Qubit Initialization in SiC
Ivády, Viktor; Klimov, Paul V.; Miao, Kevin C.; Falk, Abram L.; Christle, David J.; Szász, Krisztián; Abrikosov, Igor A.; Awschalom, David D.; Gali, Adam
2016-11-01
Dynamic nuclear polarization (DNP) is an attractive method for initializing nuclear spins that are strongly coupled to optically active electron spins because it functions at room temperature and does not require strong magnetic fields. In this Letter, we theoretically demonstrate that DNP, with near-unity polarization efficiency, can be generally realized in weakly coupled electron spin-nuclear spin systems. Furthermore, we theoretically and experimentally show that the nuclear spin polarization can be reversed by magnetic field variations as small as 0.8 Gauss. This mechanism offers new avenues for DNP-based sensors and radio-frequency free control of nuclear qubits.
Kerr-Newman Electron as Spinning Soliton
Burinskii, Alexander
2015-10-01
Measurable parameters of the electron indicate that its background should be described by the Kerr-Newman (KN) solution. The spin/mass ratio of the electron is extreme large, and the black hole horizons disappear, opening a topological defect of space-time - the Kerr singular ring of Compton size, which may be interpreted as a closed fundamental string of low energy string theory. The singular and two-sheeted structure of the corresponding Kerr space has to be regularised, and we consider the old problem of regularising the source of the KN solution. As a development of the earlier Keres-Israel-Hamity-López model, we describe the model of smooth and regular source forming a gravitating and relativistically rotating soliton based on the chiral field model and the Higgs mechanism of broken symmetry. The model reveals some new remarkable properties: (1) the soliton forms a relativistically rotating bubble of Compton radius, which is filled by the oscillating Higgs field in a pseudo-vacuum state; (2) the boundary of the bubble forms a domain wall which interpolates between the internal flat background and the external exact Kerr-Newman (KN) solution; (3) the phase transition is provided by a system of chiral fields; (4) the vector potential of the external the KN solution forms a closed Wilson loop which is quantised, giving rise to a quantised spin of the soliton; (5) the soliton is bordered by a closed string, which is a part of the general complex stringy structure.
A quantum spin transducer based on nano electro-mechancial resonator arrays
Rabl, P; Koppens, F H; Harris, J G E; Zoller, P; Lukin, M D
2009-01-01
Implementation of quantum information processing faces the contradicting requirements of combining excellent isolation to avoid decoherence with the ability to control coherent interactions in a many-body quantum system. For example, spin degrees of freedom of electrons and nuclei provide a good quantum memory due to their weak magnetic interactions with the environment. However, for the same reason it is difficult to achieve controlled entanglement of spins over distances larger than tens of nanometers. Here we propose a universal realization of a quantum data bus for electronic spin qubits where spins are coupled to the motion of magnetized mechanical resonators via magnetic field gradients. Provided that the mechanical system is charged, the magnetic moments associated with spin qubits can be effectively amplified to enable a coherent spin-spin coupling over long distances via Coulomb forces. Our approach is applicable to a wide class of electronic spin qubits which can be localized near the magnetized tip...
Shevkunov, S. V.
2016-08-01
A method for calculating the spin of the ground quantum state of nonrelativistic electrons and distance between energy levels of quantum states differing in the spin magnitude from first principles is proposed. The approach developed is free from the one-electron approximation and applicable in multielectron systems with allowance for all spatial correlations. The possibilities of the method are demonstrated by the example of calculating the energy gap between spin states in model ellipsoidal quantum dots with a harmonic confining field. The results of computations by the Monte Carlo method point to high sensitivity of the energy gap to the break of spherical symmetry of the quantum dot. For three electrons, the phenomenon of inversion has been revealed for levels corresponding to high and low values of the spin. The calculations demonstrate the practical possibility to obtain spin states with arbitrarily close energies by varying the shape of the quantum dot, which is a key condition for development prospects in technologies of storage systems based on spin qubits.
Resonance fluorescence and electron spin in semiconductor quantum dots
Zhao, Yong
2009-11-18
The work presented in this dissertation contains the first observation of spin-resolved resonance fluorescence from a single quantum dot and its application of direct measurement of electron spin dynamics. The Mollow triplet and the Mollow quintuplet, which are the hallmarks of resonance fluorescence, are presented as the non-spin-resolved and spin-resolved resonance fluorescence spectrum, respectively. The negligible laser background contribution, the near pure radiative broadened spectrum and the anti-bunching photon statistics imply the sideband photons are background-free and near transform-limited single photons. This demonstration is a promising step towards the heralded single photon generation and electron spin readout. Instead of resolving spectrum, an alternative spin-readout scheme by counting resonance fluorescence photons under moderate laser power is demonstrated. The measurements of n-shot time-resolved resonance fluorescence readout are carried out to reveal electron spin dynamics of the measurement induced back action and the spin relaxation. Hyperfine interaction and heavy-light hole mixing are identified as the relevant mechanisms for the back action and phonon-assistant spin-orbit interaction dominates the spin relaxation. After a detailed discussion on charge-spin configurations in coupled quantum dots system, the single-shot readout on electron spin are proposed. (orig.)
Electron Spin Relaxation in Intrinsic Bulk InP Semiconductor
Ma, Hong; Wang, Lihua; Ma, Guohong
2010-01-01
Electron spin dynamics is studied by time resolved pump probe reflectivity (TRPPR) technique using the co- and counter-circularly polarized femtosecond pulses in intrinsic bulk Indium Phosphide (InP) crystal at room temperature and 70 K. The reflectivity change from bleaching into absorption enhancement is observed with increasing pump photon energy. This phenomenon can be explained in terms of the spin sensitive band filling and band gap renormalization effects. Although electron spin relaxation process at room temperature is much faster than that at 70K, carrier density dependence of electron spin relaxation shows similar tendency. With increasing carrier density, the electron spin relaxation time increases initially and then decreases after reaching a maximum value. Our experimental results agree well with the recent theoretical prediction and D'yakonov-Perel' mechanism is considered as a dominating contribution to the electron spin relaxation in intrinsic bulk InP semiconductor.
Deterministic Writing and Control of the Dark Exciton Spin Using Single Short Optical Pulses
I. Schwartz
2015-01-01
Full Text Available We demonstrate that the quantum dot-confined dark exciton forms a long-lived integer spin solid-state qubit that can be deterministically on-demand initiated in a pure state by one optical pulse. Moreover, we show that this qubit can be fully controlled using short optical pulses, which are several orders of magnitude shorter than the life and coherence times of the qubit. Our demonstrations do not require an externally applied magnetic field, and they establish that the quantum dot-confined dark exciton forms an excellent solid-state matter qubit with some advantages over the half-integer spin qubits, such as the confined electron and hole, separately. Since quantum dots are semiconductor nanostructures that allow integration of electronic and photonic components, the dark exciton may have important implications for implementations of quantum technologies consisting of semiconductor qubits.
Electron-spin dynamics in elliptically polarized light waves
Bauke, Heiko; Grobe, Rainer
2014-01-01
We investigate the coupling of the spin angular momentum of light beams with elliptical polarization to the spin degree of freedom of free electrons. It is shown that this coupling, which is of similar origin as the well-known spin-orbit coupling, can lead to spin precession. The spin-precession frequency is proportional to the product of the laser-field's intensity and its spin density. The electron-spin dynamics is analyzed by employing exact numerical methods as well as time-dependent perturbation theory based on the fully relativistic Dirac equation and on the nonrelativistic Pauli equation that is amended by a relativistic correction that accounts for the light's spin density.
Free spin quantum computation with semiconductor nanostructures
Zhang, W M; Soo, C; Zhang, Wei-Min; Wu, Yin-Zhong; Soo, Chopin
2005-01-01
Taking the excess electron spin in a unit cell of semiconductor multiple quantum-dot structure as a qubit, we can implement scalable quantum computation without resorting to spin-spin interactions. The technique of single electron tunnelings and the structure of quantum-dot cellular automata (QCA) are used to create a charge entangled state of two electrons which is then converted into spin entanglement states by using single spin rotations. Deterministic two-qubit quantum gates can also be manipulated using only single spin rotations with help of QCA. A single-short read-out of spin states can be realized by coupling the unit cell to a quantum point contact.
Spin Squeezing of Atomic Ensembles via Nuclear-Electronic Spin Entanglement
Fernholz, Thomas; Krauter, Hanna; Jensen, K.
2008-01-01
We demonstrate spin squeezing in a room temperature ensemble of ≈1012 cesium atoms using their internal structure, where the necessary entanglement is created between nuclear and electronic spins of each individual atom. This state provides improvement in measurement sensitivity beyond the standard...... quantum limit for quantum memory experiments and applications in quantum metrology and is thus a complementary alternative to spin squeezing obtained via interatom entanglement. Squeezing of the collective spin is verified by quantum state tomography....
Spin Squeezing of Atomic Ensembles via Nuclear-Electronic Spin Entanglement
Fernholz, Thomas; Krauter, Hanna; Jensen, K.;
2008-01-01
We demonstrate spin squeezing in a room temperature ensemble of ≈1012 cesium atoms using their internal structure, where the necessary entanglement is created between nuclear and electronic spins of each individual atom. This state provides improvement in measurement sensitivity beyond the standard...... quantum limit for quantum memory experiments and applications in quantum metrology and is thus a complementary alternative to spin squeezing obtained via interatom entanglement. Squeezing of the collective spin is verified by quantum state tomography....
Single-qubit remote manipulation by magnetic solitons
Cuccoli, Alessandro, E-mail: cuccoli@fi.infn.it [Dipartimento di Fisica e Astronomia, Università di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); CNISM – c/o Dipartimento di Fisica e Astronomia, Università di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Nuzzi, Davide, E-mail: nuzzi@fi.infn.it [Dipartimento di Fisica e Astronomia, Università di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Vaia, Ruggero, E-mail: ruggero.vaia@isc.cnr.it [Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, via Madonna del Piano 10, I-50019 Sesto Fiorentino (Italy); Verrucchi, Paola, E-mail: verrucchi@fi.infn.it [Dipartimento di Fisica e Astronomia, Università di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Istituto Nazionale di Fisica Nucleare, Sezione di Firenze, via G. Sansone 1, I-50019 Sesto Fiorentino (Italy); Istituto dei Sistemi Complessi, Consiglio Nazionale delle Ricerche, via Madonna del Piano 10, I-50019 Sesto Fiorentino (Italy)
2016-02-15
Magnetic solitons can constitute a means for manipulating qubits from a distance. This would overcome the necessity of directly applying selective magnetic fields, which is unfeasible in the case of a matrix of qubits embedded in a solid-state quantum device. If the latter contained one-dimensional Heisenberg spin chains coupled to each qubit, one can originate a soliton in a selected chain by applying a time-dependent field at one end of it, far from the qubits. The generation of realistic solitons has been simulated. When a suitable soliton passes by, the coupled qubit undergoes nontrivial operations, even in the presence of moderate thermal noise. - Highlights: • Proposal for the remote control of qubits coupled to a spin chain supporting solitons. • Traveling solitons can be generated on the chain by acting far from the qubit. • Suitable magnetic solitons can properly change the qubit state. • This qubit manipulation mechanism is shown to be resilient to thermal noise.
Spin polarization of electrons with Rashba double-refraction
Ramaglia, V Marigliano; Bercioux, D; Cataudella, V; De Filippis, G; Perroni, C A [Coherentia-INFM and Dipartimento di Scienze Fisiche Universita degli Studi Federico II, Naples, I-80126 (Italy)
2004-12-22
We demonstrate how the Rashba spin-orbit coupling in semiconductor heterostructures can produce and control a spin-polarized current without ferromagnetic leads. The key idea is to use spin-double refraction of an electronic beam with a nonzero incidence angle. A region where the spin-orbit coupling is present separates the source and the drain without spin-orbit coupling. We show how the transmission and the beam spin polarization critically depend on the incidence angle. The transmission halves when the incidence angle is greater than a limit angle and a significant spin polarization appears. On increasing the spin-orbit coupling one can obtain the modulation of the intensity and of the spin polarization of the output electronic current when the input current is unpolarized. Our analysis shows the possibility of realizing a spin-field-effect transistor based on the propagation of only one mode with the region with spin-orbit coupling, whereas the original Datta and Das device (1990 Appl. Phys. Lett. 56 665) uses the spin precession that originates from the interference between two modes with orthogonal spin.
Optically programmable electron spin memory using semiconductor quantum dots.
Kroutvar, Miro; Ducommun, Yann; Heiss, Dominik; Bichler, Max; Schuh, Dieter; Abstreiter, Gerhard; Finley, Jonathan J
2004-11-04
The spin of a single electron subject to a static magnetic field provides a natural two-level system that is suitable for use as a quantum bit, the fundamental logical unit in a quantum computer. Semiconductor quantum dots fabricated by strain driven self-assembly are particularly attractive for the realization of spin quantum bits, as they can be controllably positioned, electronically coupled and embedded into active devices. It has been predicted that the atomic-like electronic structure of such quantum dots suppresses coupling of the spin to the solid-state quantum dot environment, thus protecting the 'spin' quantum information against decoherence. Here we demonstrate a single electron spin memory device in which the electron spin can be programmed by frequency selective optical excitation. We use the device to prepare single electron spins in semiconductor quantum dots with a well defined orientation, and directly measure the intrinsic spin flip time and its dependence on magnetic field. A very long spin lifetime is obtained, with a lower limit of about 20 milliseconds at a magnetic field of 4 tesla and at 1 kelvin.
Lin, D.P.; Kevan, L.
1977-05-19
Electron--electron double resonance (ELDOR) has been used to test the validity of the noninteracting spin packet model for inhomogeneously broadened ESR lines. For trapped electrons in 10M NaOD/D/sub 2/O glassy ice the saturation of field-swept ELDOR spectra fits the above mentioned model in contrast to earlier work on trapped electrons in protiated matrices. In the protiated matrix spin diffusion produces significant interaction between the spin packets. The difference between the protiated and deuterated matrices suggests that nuclear relaxation is the mechanism for spin diffusion. The deuterated matrices show no structure in frequency-swept ELDOR spectra due to deuteron spin--flip transitions whereas structure due to proton spin--flips is seen in protiated matrices.
Structure dependent spin selectivity in electron transport through oligopeptides
Kiran, Vankayala; Cohen, Sidney R.; Naaman, Ron
2017-03-01
The chiral-induced spin selectivity (CISS) effect entails spin-selective electron transmission through chiral molecules. In the present study, the spin filtering ability of chiral, helical oligopeptide monolayers of two different lengths is demonstrated using magnetic conductive probe atomic force microscopy. Spin-specific nanoscale electron transport studies elucidate that the spin polarization is higher for 14-mer oligopeptides than that of the 10-mer. We also show that the spin filtering ability can be tuned by changing the tip-loading force applied on the molecules. The spin selectivity decreases with increasing applied force, an effect attributed to the increased ratio of radius to pitch of the helix upon compression and increased tilt angles between the molecular axis and the surface normal. The method applied here provides new insights into the parameters controlling the CISS effect.
He, Jianhua; Malissa, H.; Lu, Tzu-Ming; Shankar, S.; Tyryshkin, A. M.; Lyon, S. A.; Chen, Hung-Ming; Kuan, Chieh-Hsiung
2010-03-01
Electron spins in quantum dots in Si/SiGe heterostructures are promising qubits but controlling and measuring spins in gated dots is challenging. Fortunately, electrons confined into natural quantum dots by interface disorder can capture the spin physics with minimal processing, exhibiting long T1 and T2 at the Si/SiO2 interface^1. Natural quantum dots in the Si/SiGe system may be similarly useful. As a first step, we have fabricated a 2.2 x 13mm^2 Hall bar on a Si/SiGe substrate gated with an Al gate above an Al2O3 insulator, and performed electron spin resonance (ESR) at gate voltages above and below threshold. The ESR signal arising from the Si quantum well evolves with gate voltage, and its intensity (spin susceptibility) is measured as a function of temperature down to 0.4K. The susceptibility follows a Pauli dependence when the gate is biased above threshold, while it is Curie-like below threshold, indicating an evolution from a mobile 2D system towards localized states confined in natural dots by the intrinsic disorder in the quantum well. This work is supported by LPS and ARO. [1] S. Shankar, et al., Physica E, 40, 1659-1661 (2008).
Spin orbit torque based electronic neuron
Sengupta, Abhronil, E-mail: asengup@purdue.edu; Choday, Sri Harsha; Kim, Yusung; Roy, Kaushik [School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907 (United States)
2015-04-06
A device based on current-induced spin-orbit torque (SOT) that functions as an electronic neuron is proposed in this work. The SOT device implements an artificial neuron's thresholding (transfer) function. In the first step of a two-step switching scheme, a charge current places the magnetization of a nano-magnet along the hard-axis, i.e., an unstable point for the magnet. In the second step, the SOT device (neuron) receives a current (from the synapses) which moves the magnetization from the unstable point to one of the two stable states. The polarity of the synaptic current encodes the excitatory and inhibitory nature of the neuron input and determines the final orientation of the magnetization. A resistive crossbar array, functioning as synapses, generates a bipolar current that is a weighted sum of the inputs. The simulation of a two layer feed-forward artificial neural network based on the SOT electronic neuron shows that it consumes ∼3× lower power than a 45 nm digital CMOS implementation, while reaching ∼80% accuracy in the classification of 100 images of handwritten digits from the MNIST dataset.
Kerr-Newman electron as spinning soliton
Burinskii, Alexander
2014-01-01
Measurable parameters of the electron indicate that its background should be described by the Kerr-Newman (KN) solution. Spin/mass ratio of the electron is extreme large, and the black hole horizons disappear, opening a topological defect of spacetime -- the Kerr singular ring of the Compton size, which may be interpreted as a closed fundamental string to the low energy string theory. The singular and twosheeted structure of the corresponding Kerr space has to be regularized, and we consider the old problem of regular source of the KN solution. As a development of the earlier Keres-Israel-Hamity-L\\'opez model, we describe the model of smooth and regular source forming a gravitating and relativistically rotating soliton based on the chiral field model and the Higgs mechanism of broken symmetry. The model reveals some new remarkable properties: 1) the soliton forms a relativistically rotating bubble of the Compton radius, which is filled by the oscillating Higgs field in pseudo-vacuum state, 2) boundary of the ...
Polarization Measurement of Spin-Polarized Electrons by Optical Electron Polarimeter
DING Hai-Bing; PANG Wen-Ning; LIU Yi-Bao; SHANG Ren-Cheng
2005-01-01
@@ The polarization of spin-polarized electrons, produced from a new GaAs spin-polarized electron source, is determined by an optical electron polarimeter. The He 3 3p → 23S1 (388.9nm) transition is used for the optical electron polarimetry. The structure and performance of the experimental setup of spin-polarized electron source and optical electron polarimeter are described. The result of polarization of 30.8% averaged spin-up and spindown polarized electrons is obtained and presented.
Universal Synchronous Spin Rotators for Electron-Ion Colliders
Chevtsov, Pavel; Krafft, Geoff; Zhang, Yuhong
2016-01-01
The paper provides mathematics and physics considerations concerning a special class of electron spin manipulating structures for future Electron-Ion Collider (EIC) projects. These structures, which we call Universal Synchronous Spin Rotators (USSR), consist of a sequence of standard basic spin manipulating elements or cells built with two solenoids and one bending magnet between them. When integrated into the ring arcs, USSR structures do not affect the central particle orbit, and their spin transformation functions can be described by a linear mathematical model. In spite of being relatively simple, the model allows one to design spin rotators, which are able to perform spin direction changes from vertical to longitudinal and vice versa in significant continuous intervals of the electron energy. This makes USSR especially valuable tools for EIC nuclear physics experiments.
Frenkel electron and a spinning body in a curved background
Ramírez, Walberto Guzmán; Pupasov-Maksimov, Andrey M
2014-01-01
We develop variational formulation of a particle with spin in a curved space-time background. The model is based on a singular Lagrangian which provides equations of motion, fixed value of spin and Frenkel condition on spin-tensor. Comparing our equations with those of Papapetrou, we conclude that the Frenkel electron in gravitational field has the same behavior as a rotating body in pole-dipole and leading-spin approximation. Due to constraints presented in the formulation, position space is endowed with noncommutative structure induced by spin of the particle. Therefore the model provides physically interesting example of noncommutative particle in a curved background.
Heralded entanglement between solid-state qubits separated by three metres.
Bernien, H; Hensen, B; Pfaff, W; Koolstra, G; Blok, M S; Robledo, L; Taminiau, T H; Markham, M; Twitchen, D J; Childress, L; Hanson, R
2013-05-01
Quantum entanglement between spatially separated objects is one of the most intriguing phenomena in physics. The outcomes of independent measurements on entangled objects show correlations that cannot be explained by classical physics. As well as being of fundamental interest, entanglement is a unique resource for quantum information processing and communication. Entangled quantum bits (qubits) can be used to share private information or implement quantum logical gates. Such capabilities are particularly useful when the entangled qubits are spatially separated, providing the opportunity to create highly connected quantum networks or extend quantum cryptography to long distances. Here we report entanglement of two electron spin qubits in diamond with a spatial separation of three metres. We establish this entanglement using a robust protocol based on creation of spin-photon entanglement at each location and a subsequent joint measurement of the photons. Detection of the photons heralds the projection of the spin qubits onto an entangled state. We verify the resulting non-local quantum correlations by performing single-shot readout on the qubits in different bases. The long-distance entanglement reported here can be combined with recently achieved initialization, readout and entanglement operations on local long-lived nuclear spin registers, paving the way for deterministic long-distance teleportation, quantum repeaters and extended quantum networks.
Witzel, Wayne M.; Montaño, Inès; Muller, Richard P.; Carroll, Malcolm S.
2015-08-01
We present a strategy for producing multiqubit gates that promise high fidelity with minimal tuning requirements. Our strategy combines gap protection from the adiabatic theorem with dynamical decoupling in a complementary manner. Energy-level transition errors are protected by adiabaticity and remaining phase errors are mitigated via dynamical decoupling. This is a powerful way to divide and conquer the various error channels. In order to accomplish this without violating a no-go theorem regarding black-box dynamically corrected gates [Phys. Rev. A 80, 032314 (2009), 10.1103/PhysRevA.80.032314], we require a robust operating point (sweet spot) in control space where the qubits interact with little sensitivity to noise. There are also energy gap requirements for effective adiabaticity. We apply our strategy to an architecture in Si with P donors where we assume we can shuttle electrons between different donors. Electron spins act as mobile ancillary qubits and P nuclear spins act as long-lived data qubits. This system can have a very robust operating point where the electron spin is bound to a donor in the quadratic Stark shift regime. High fidelity single qubit gates may be performed using well-established global magnetic resonance pulse sequences. Single electron-spin preparation and measurement has also been demonstrated. Putting this all together, we present a robust universal gate set for quantum computation.
High Fidelity Single Qubit Operations using Pulsed EPR
Morton, J J L; Ardavan, A; Porfyrakis, K; Lyon, S A; Briggs, G A D; Morton, John J. L.; Tyryshkin, Alexei M.; Ardavan, Arzhang; Porfyrakis, Kyriakos
2005-01-01
The fidelity of quantum logic operations performed on electron spin qubits using simple RF pulses falls well below the threshold for the application of quantum algorithms. Using three independent techniques, we demonstrate the use of composite pulses to improve this fidelity by several orders of magnitude. The observed high-fidelity operations are limited by pulse phase errors, but nevertheless fall within the limits required for the application of quantum error correction algorithms.
Electron-Nuclear Spin Transfer in Triple Quantum Dot Networks
Prada, Marta; Toonen, Ryan; Harrison, Paul
2005-03-01
We investigate the conductance spectra of coupled quantum dots to study systematically the nuclear spin relaxation of delta- and y-junction networks and observe spin blockade dependence on the electronic configurations. We derive the conductance using the Beenakker approach generalised to an array of quantum dots where we consider the nuclear spin transfer to electrons by hyperfine coupling. This allows us to predict the relevant memory effects on the different electronic states by studying the evolution of the single electron resonances in presence of nuclear spin relaxation. We find that the gradual depolarisation of the nuclear system is imprinted in the conductance spectra of the multidot system. Our calculations of the temporal evolution of the conductance resonance reveal that spin blockade can be lifted by hyperfine coupling.
Electron nuclear spin transfer in quantum-dot networks
Prada, M.; Toonen, R. C.; Blick, R. H.; Harrison, P.
2005-05-01
We investigate the conductance spectra of coupled quantum dots to study systematically the nuclear spin relaxation of different geometries of a two-dimensional network of quantum dots and observe spin blockade dependence on the electronic configurations. We derive the conductance using the Beenakker approach generalized to an array of quantum dots where we consider the nuclear spin transfer to electrons by hyperfine coupling. This allows us to predict the relevant memory effects on the different electronic states by studying the evolution of the single electron resonances in the presence of nuclear spin relaxation. We find that the gradual depolarization of the nuclear system is imprinted in the conductance spectra of the multidot system. Our calculations of the temporal evolution of the conductance resonance reveal that spin blockade can be lifted by hyperfine coupling.
Optical detection of spin-filter effect for electron spin polarimetry
Li, X.; Majee, S.; Lampel, G.; Lassailly, Y.; Paget, D.; Peretti, J. [Laboratoire de Physique de la Matière Condensée, Ecole Polytechnique - CNRS, 91128 Palaiseau Cedex (France); Tereshchenko, O. E., E-mail: teresh@isp.nsc.ru [Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk 630090 (Russian Federation); Novosibirsk State University, Novosibirsk 630090 (Russian Federation)
2014-08-04
We have monitored the cathodoluminescence (CL) emitted upon injection of free electrons into a hybrid structure consisting of a thin magnetic Fe layer deposited on a p-GaAs substrate, in which InGaAs quantum wells are embedded. Electrons transmitted through the unbiased metal/semiconductor junction recombine radiatively in the quantum wells. Because of the electron spin-filtering across the Fe/GaAs structure, the CL intensity, collected from the backside, is found to depend on the relative orientation between the injected electronic spin polarization and the Fe layer magnetization. The spin asymmetry of the CL intensity in such junction provides a compact optical method for measuring spin polarization of free electrons beams or of hot electrons in solid-state devices.
Quantum many-body theory for electron spin decoherence in nanoscale nuclear spin baths
Yang, Wen; Ma, Wen-Long; Liu, Ren-Bao
2017-01-01
Decoherence of electron spins in nanoscale systems is important to quantum technologies such as quantum information processing and magnetometry. It is also an ideal model problem for studying the crossover between quantum and classical phenomena. At low temperatures or in light-element materials where the spin-orbit coupling is weak, the phonon scattering in nanostructures is less important and the fluctuations of nuclear spins become the dominant decoherence mechanism for electron spins. Since the 1950s, semi-classical noise theories have been developed for understanding electron spin decoherence. In spin-based solid-state quantum technologies, the relevant systems are in the nanometer scale and nuclear spin baths are quantum objects which require a quantum description. Recently, quantum pictures have been established to understand the decoherence and quantum many-body theories have been developed to quantitatively describe this phenomenon. Anomalous quantum effects have been predicted and some have been experimentally confirmed. A systematically truncated cluster-correlation expansion theory has been developed to account for the many-body correlations in nanoscale nuclear spin baths that are built up during electron spin decoherence. The theory has successfully predicted and explained a number of experimental results in a wide range of physical systems. In this review, we will cover this recent progress. The limitations of the present quantum many-body theories and possible directions for future development will also be discussed.
Quantum many-body theory for electron spin decoherence in nanoscale nuclear spin baths.
Yang, Wen; Ma, Wen-Long; Liu, Ren-Bao
2017-01-01
Decoherence of electron spins in nanoscale systems is important to quantum technologies such as quantum information processing and magnetometry. It is also an ideal model problem for studying the crossover between quantum and classical phenomena. At low temperatures or in light-element materials where the spin-orbit coupling is weak, the phonon scattering in nanostructures is less important and the fluctuations of nuclear spins become the dominant decoherence mechanism for electron spins. Since the 1950s, semi-classical noise theories have been developed for understanding electron spin decoherence. In spin-based solid-state quantum technologies, the relevant systems are in the nanometer scale and nuclear spin baths are quantum objects which require a quantum description. Recently, quantum pictures have been established to understand the decoherence and quantum many-body theories have been developed to quantitatively describe this phenomenon. Anomalous quantum effects have been predicted and some have been experimentally confirmed. A systematically truncated cluster-correlation expansion theory has been developed to account for the many-body correlations in nanoscale nuclear spin baths that are built up during electron spin decoherence. The theory has successfully predicted and explained a number of experimental results in a wide range of physical systems. In this review, we will cover this recent progress. The limitations of the present quantum many-body theories and possible directions for future development will also be discussed.
Qubit State Monitoring by Measurement of Three Complementary Observables
Ruskov, Rusko; Korotkov, Alexander N.; Mølmer, Klaus
2010-01-01
We consider the evolution of a qubit (spin 1/2) under the simultaneous continuous measurement of three noncommuting qubit operators σ̂x, σ̂y, and σ̂z. For identical ideal detectors, the qubit state evolves by approaching a pure state with a random direction in the Bloch vector space...
Decoherence-protected quantum gates for a hybrid solid-state spin register.
van der Sar, T; Wang, Z H; Blok, M S; Bernien, H; Taminiau, T H; Toyli, D M; Lidar, D A; Awschalom, D D; Hanson, R; Dobrovitski, V V
2012-04-04
Protecting the dynamics of coupled quantum systems from decoherence by the environment is a key challenge for solid-state quantum information processing. An idle quantum bit (qubit) can be efficiently insulated from the outside world by dynamical decoupling, as has recently been demonstrated for individual solid-state qubits. However, protecting qubit coherence during a multi-qubit gate is a non-trivial problem: in general, the decoupling disrupts the interqubit dynamics and hence conflicts with gate operation. This problem is particularly salient for hybrid systems, in which different types of qubit evolve and decohere at very different rates. Here we present the integration of dynamical decoupling into quantum gates for a standard hybrid system, the electron-nuclear spin register. Our design harnesses the internal resonance in the coupled-spin system to resolve the conflict between gate operation and decoupling. We experimentally demonstrate these gates using a two-qubit register in diamond operating at room temperature. Quantum tomography reveals that the qubits involved in the gate operation are protected as accurately as idle qubits. We also perform Grover's quantum search algorithm, and achieve fidelities of more than 90% even though the algorithm run-time exceeds the electron spin dephasing time by two orders of magnitude. Our results directly allow decoherence-protected interface gates between different types of solid-state qubit. Ultimately, quantum gates with integrated decoupling may reach the accuracy threshold for fault-tolerant quantum information processing with solid-state devices.
Bang-bang control of fullerene qubits using ultra-fast phase gates
Morton, J J L; Ardavan, A; Benjamin, S C; Porfyrakis, K; Lyon, S A; Briggs, G A D; Morton, John J. L.; Tyryhskin, Alexei M.; Ardavan, Arzhang; Benjamin, Simon C.; Porfyrakis, Kyriakos
2006-01-01
Quantum mechanics permits an entity, such as an atom, to exist in a superposition of multiple states simultaneously. Quantum information processing (QIP) harnesses this profound phenomenon to manipulate information in radically new ways. A fundamental challenge in all QIP technologies is the corruption of superposition in a quantum bit (qubit) through interaction with its environment. Quantum bang-bang control provides a solution by repeatedly applying `kicks' to a qubit, thus disrupting an environmental interaction. However, the speed and precision required for the kick operations has presented an obstacle to experimental realization. Here we demonstrate a phase gate of unprecedented speed on a nuclear spin qubit in a fullerene molecule (N@C60), and use it to bang-bang decouple the qubit from a strong environmental interaction. We can thus trap the qubit in closed cycles on the Bloch sphere, or lock it in a given state for an arbitrary period. Our procedure uses operations on a second qubit, an electron spin...
Entanglement manifestation in spin resolved electron–electron scattering
Artamonov, O.M., E-mail: artaoleg@gmail.com [Institute of Physics, St Petersburg State University, St Petersburg (Russian Federation); Samarin, S.N., E-mail: sergey.samarin@uwa.edu.au [Institute of Physics, St Petersburg State University, St Petersburg (Russian Federation); School of Physics, the University of Western Australia, Crawley, Perth 6009, WA (Australia); Vetlugin, A.N.; Sokolov, I.V. [Institute of Physics, St Petersburg State University, St Petersburg (Russian Federation); Williams, J.F. [School of Physics, the University of Western Australia, Crawley, Perth 6009, WA (Australia)
2015-11-15
Highlights: • Spin entangled pairs is created by the Coulomb scattering of polarized electrons. • Polarization and separability of scattered electrons is investigated. • The model comparison with the experimental results shows qualitative agreement. • Analytical correlation between polarization and separability of pairs is found. - Abstract: The polarization vector P of scattered electrons interacting with a polarized target electrons is compared with the entanglement (or non-separability) of the electron states of the interacting electron pair. The separability S is defined as a linear function of the von Neumann entropy. The shapes of the functions P (θ,Ω,φ) and S (θ,Ω,φ) are similar and simultaneously achieve their maximum value at the scattering angle θ values close to 0 and π and simultaneously tend to zero in the case of symmetric scattering at θ ≈ π/2. In the latter case the scattered electrons are described by an asymmetric spin part of the wave function, which by definition corresponds to the spin entangled (S ≈ 0) electron states of the interacting electron pair. Comparison of the model calculation results with experimental results of the spin polarized electron spectroscopy of the ferromagnetic solid shows qualitative agreement. The analytical expression relating polarization and separability of the two interacting particles enables use the measured polarization of scattered electrons for estimation of the spin-entanglement or separability of the two particle systems.
Electron spin control of optically levitated nanodiamonds in vacuum
Hoang, Thai M.; Ahn, Jonghoon; Bang, Jaehoon; Li, Tongcang
2016-07-01
Electron spins of diamond nitrogen-vacancy (NV) centres are important quantum resources for nanoscale sensing and quantum information. Combining NV spins with levitated optomechanical resonators will provide a hybrid quantum system for novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centres in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this system, we investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect. We also observe that oxygen and helium gases have different effects on both the photoluminescence and the ESR contrast of nanodiamond NV centres, indicating potential applications of NV centres in oxygen gas sensing. Our results pave the way towards a levitated spin-optomechanical system for studying macroscopic quantum mechanics.
Electron spin control of optically levitated nanodiamonds in vacuum.
Hoang, Thai M; Ahn, Jonghoon; Bang, Jaehoon; Li, Tongcang
2016-07-19
Electron spins of diamond nitrogen-vacancy (NV) centres are important quantum resources for nanoscale sensing and quantum information. Combining NV spins with levitated optomechanical resonators will provide a hybrid quantum system for novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centres in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this system, we investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect. We also observe that oxygen and helium gases have different effects on both the photoluminescence and the ESR contrast of nanodiamond NV centres, indicating potential applications of NV centres in oxygen gas sensing. Our results pave the way towards a levitated spin-optomechanical system for studying macroscopic quantum mechanics.
Orbital hyperfine interaction and qubit dephasing in carbon nanotube quantum dots
Palyi, Andras; Csiszar, Gabor
2015-03-01
Hyperfine interaction (HF) is of key importance for the functionality of solid-state quantum information processing, as it affects qubit coherence and enables nuclear-spin quantum memories. In this work, we complete the theory of the basic hyperfine interaction mechanisms (Fermi contact, dipolar, orbital) in carbon nanotube quantum dots by providing a theoretical description of the orbital HF. We find that orbital HF induces an interaction between the nuclear spins of the nanotube lattice and the valley degree of freedom of the electrons confined in the quantum dot. We show that the resulting nuclear-spin-electron-valley interaction (i) is approximately of Ising type, (ii) is essentially local, in the sense that an effective atomic interaction strength can be defined, and (iii) has a strength that is comparable to the combined strength of Fermi contact and dipolar interactions. We argue that orbital HF provides a new decoherence mechanism for single-electron valley qubits and spin-valley qubits in a range of multi-valley materials. We explicitly evaluate the corresponding inhomogeneous dephasing time T2* for a nanotube-based valley qubit. We acknowledge funding from the EU Marie Curie CIG-293834, OTKA Grant PD 100373, and EU ERC Starting Grant CooPairEnt 258789. AP is supported by the Janos Bolyai Scholarship of the Hungarian Academy of Sciences.
Cho, Franklin; Takahashi, Susumu
2014-03-01
Nano-sized diamond or nanodiamond is a fascinating material for potential applications of fluorescence imaging and magnetic sensing of biological systems via nitrogen-vacancy defect centers in diamonds. Sensitivity of the magnetic sensing strongly depends on coupling to surrounding environmental noises, thus understanding of the environment is critical to realize the application. In the present study, we employ multi-frequency (X-band, 115 GHz and 230 GHz) continuous-wave (cw) and pulsed electron spin resonance (ESR) spectroscopy to investigate impurity contents and spin relaxation properties in various sizes of nanodiamonds. Spectra taken with our home-built 230/115 GHz cw/pulsed ESR spectrometer shows presence of two major impurity contents; single substitutional nitrogen impurities (P1) also common in bulk diamonds and paramagnetic impurities (denoted as X) unique to nanodiamonds. The ESR measurement also shows a strong dependence of the population ratio between P1 and X on particle size. Furthermore, we will discuss the nature of spin-lattice relaxation time T1 of nanodiamonds studied by pulsed ESR measurements at X-band, 115 GHz and 230 GHz.
Electron with arbitrary pseudo-spins in multilayer graphene
Worasak Prarokijjak; Bumned Soodchomshom
2015-01-01
Using the low-energy effective Hamiltonian of the ABC-stacked multilayer graphene, the pseudo-spin coupling to real orbital angular momentum of electrons in multilayer graphene is investigated. We show that the electron wave function in N-layer graphene mimics the behavior of a particle with a spin of N × (}/2), where N={1, 2, 3, . . .}. It is said that for N>1 the low-energy effective Hamiltonian for ABC-stacked graphene cannot be used to describe pseudo-spin-1/2 particles. The wave function of electrons in multilayer graphene may behave like fermionic (or bosonic) particle for N being odd (or even). In this paper, we propose a theory of graphene serving as a host material of electrons with arbitrary pseudo-spins tunable by changing the number of graphene layers.
Coupling of Photonic and Electronic Spin Catalyzed by Diatomic Molecules
Gay, Timothy
2011-05-01
Recent experiments involving the collisions of polarized photons or polarized electrons with simple diatomic molecules have shown novel ways in which the net spin of electrons can be converted into the net spin of photons following the collisions, or vice versa. I will discuss three recent experiments that illustrate such transformations: the production of nuclear rotational spin in nitrogen molecules excited by polarized electrons with the subsequent emission of polarized photons, the excitation by polarized electrons of rotational eigenstates of hydrogen molecules and the subsequent emission of circularly-polarized light, and the photolysis of hydrogen molecules by circularly-polarized light yielding photofragments that ``spin the wrong way.'' To our knowledge, these latter measurements represent the first observation of photofragment orientation by direct observation of the polarization of the photofragment fluoresence. Work supported by the NSF through grant PHY-0821385, the DOE through the use of the ALS at LBL, and ANSTO (Access to Major Research Facilities Programme).
Spin structure of electron subbands in (110)-grown quantum wells
Nestoklon, M. O.; Tarasenko, S. A. [Ioffe Physical-Technical Institute, Russian Academy of Sciences, St. Petersburg 194021 (Russian Federation); Jancu, J.-M. [FOTON-INSA Laboratory, UMR 6082 au CNRS, INSA de Rennes, 35043 Rennes Cedex (France); Voisin, P. [CNRS-Laboratoire de Photonique et de Nanostructures, 91460 Marcoussis (France)
2013-12-04
We present the theory of fine structure of electron states in symmetric and asymmetric zinc-blende-type quantum wells with the (110) crystallographic orientation. By combining the symmetry analysis, sp{sup 3}d{sup 5}s* tight-binding method, and envelope-function approach we obtain quantitative description of in-plane wave vector, well width and applied electric field dependencies of the zero-magnetic-field spin splitting of electron subbands and extract spin-orbit-coupling parameters.
Two-dimensional supramolecular electron spin arrays.
Wäckerlin, Christian; Nowakowski, Jan; Liu, Shi-Xia; Jaggi, Michael; Siewert, Dorota; Girovsky, Jan; Shchyrba, Aneliia; Hählen, Tatjana; Kleibert, Armin; Oppeneer, Peter M; Nolting, Frithjof; Decurtins, Silvio; Jung, Thomas A; Ballav, Nirmalya
2013-05-07
A bottom-up approach is introduced to fabricate two-dimensional self-assembled layers of molecular spin-systems containing Mn and Fe ions arranged in a chessboard lattice. We demonstrate that the Mn and Fe spin states can be reversibly operated by their selective response to coordination/decoordination of volatile ligands like ammonia (NH3). Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Foucault's pendulum, a classical analog for the electron spin state
Linck, Rebecca A.
Spin has long been regarded as a fundamentally quantum phenomena that is incapable of being described classically. To bridge the gap and show that aspects of spin's quantum nature can be described classically, this work uses a classical Lagrangian based on the coupled oscillations of Foucault's pendulum as an analog for the electron spin state in an external magnetic field. With this analog it is possible to demonstrate that Foucault's pendulum not only serves as a basis for explaining geometric phase, but is also a basis for reproducing a broad range of behavior from Zeeman-like frequency splitting to precession of the spin state. By demonstrating that unmeasured electron spin states can be fully described in classical terms, this research opens the door to using the tools of classical physics to examine an inherently quantum phenomenon.
Electron spin relaxation in cryptochrome-based magnetoreception
Kattnig, Daniel R; Solov'yov, Ilia A; Hore, P J
2016-01-01
The magnetic compass sense of migratory birds is thought to rely on magnetically sensitive radical pairs formed photochemically in cryptochrome proteins in the retina. An important requirement of this hypothesis is that electron spin relaxation is slow enough for the Earth's magnetic field to have...... a significant effect on the coherent spin dynamics of the radicals. It is generally assumed that evolutionary pressure has led to protection of the electron spins from irreversible loss of coherence in order that the underlying quantum dynamics can survive in a noisy biological environment. Here, we address...... this question for a structurally characterized model cryptochrome expected to share many properties with the putative avian receptor protein. To this end we combine all-atom molecular dynamics simulations, Bloch-Redfield relaxation theory and spin dynamics calculations to assess the effects of spin relaxation...
Spin Relaxation in GaAs: Importance of Electron-Electron Interactions
Gionni Marchetti
2014-04-01
Full Text Available We study spin relaxation in n-type bulk GaAs, due to the Dyakonov–Perel mechanism, using ensemble Monte Carlo methods. Our results confirm that spin relaxation time increases with the electronic density in the regime of moderate electronic concentrations and high temperature. We show that the electron-electron scattering in the non-degenerate regime significantly slows down spin relaxation. This result supports predictions by Glazov and Ivchenko. Most importantly, our findings highlight the importance of many-body interactions for spin dynamics: we show that only by properly taking into account electron-electron interactions within the simulations, results for the spin relaxation time—with respect to both electron density and temperature—will reach good quantitative agreement with corresponding experimental data. Our calculations contain no fitting parameters.
Pan, Xin-Yu; Yang, Li-Li; Fan, Heng
2010-01-01
Here we report an experimental realization of optimal phase-covariant quantum cloning machine with a single electron spin in solid state system at room temperature. The involved three states of two logic qubits are encoded physically in three levels of a single electron spin with two Zeeman sub-levels at a nitrogen-vacancy defect center in diamond. The preparation of input state and the phase-covariant quantum cloning transformation are controlled by two independent microwave fields. The center can be optically spin-polarized and the output state can be measured by combining confocal microscopy technique with spin-selective rates of fluorescence. The measured intensities of fluorescence of the output state are fitted in data of Rabi oscillations to find the exact form of the output. We provide the first solid-state proof-of-concept demonstration of the optimal phase-covariant quantum cloning. The combination of two microwave fields provides a technique to precisely control and measure a three-level superposed...
Isolated electron spins in silicon carbide with millisecond coherence times
Christle, David J.; Falk, Abram L.; Andrich, Paolo; Klimov, Paul V.; Hassan, Jawad Ul; Son, Nguyen T.; Janzén, Erik; Ohshima, Takeshi; Awschalom, David D.
2015-02-01
The elimination of defects from SiC has facilitated its move to the forefront of the optoelectronics and power-electronics industries. Nonetheless, because certain SiC defects have electronic states with sharp optical and spin transitions, they are increasingly recognized as a platform for quantum information and nanoscale sensing. Here, we show that individual electron spins in high-purity monocrystalline 4H-SiC can be isolated and coherently controlled. Bound to neutral divacancy defects, these states exhibit exceptionally long ensemble Hahn-echo spin coherence times, exceeding 1 ms. Coherent control of single spins in a material amenable to advanced growth and microfabrication techniques is an exciting route towards wafer-scale quantum technologies.
Gräfenstein, Jürgen; Cremer, Dieter
2004-12-22
For the first time, the nuclear magnetic resonance (NMR) spin-spin coupling mechanism is decomposed into one-electron and electron-electron interaction contributions to demonstrate that spin-information transport between different orbitals is not exclusively an electron-exchange phenomenon. This is done using coupled perturbed density-functional theory in conjunction with the recently developed J-OC-PSP [=J-OC-OC-PSP: Decomposition of J into orbital contributions using orbital currents and partial spin polarization)] method. One-orbital contributions comprise Ramsey response and self-exchange effects and the two-orbital contributions describe first-order delocalization and steric exchange. The two-orbital effects can be characterized as external orbital, echo, and spin transport contributions. A relationship of these electronic effects to zeroth-order orbital theory is demonstrated and their sign and magnitude predicted using simple models and graphical representations of first order orbitals. In the case of methane the two NMR spin-spin coupling constants result from totally different Fermi contact coupling mechanisms. (1)J(C,H) is the result of the Ramsey response and the self-exchange of the bond orbital diminished by external first-order delocalization external one-orbital effects whereas (2)J(H,H) spin-spin coupling is almost exclusively mitigated by a two-orbital steric exchange effect. From this analysis, a series of prediction can be made how geometrical deformations, electron lone pairs, and substituent effects lead to a change in the values of (1)J(C,H) and (2)J(H,H), respectively, for hydrocarbons.
Spin-polarizing interferometric beam splitter for free electrons
Dellweg, Matthias M
2016-01-01
A spin-polarizing electron beam splitter is described which relies on an arrangement of linearly polarized laser waves of nonrelativistic intensity. An incident electron beam is first coherently scattered off a bichromatic laser field, splitting the beam into two portions, with electron spin and momentum being entangled. Afterwards, the partial beams are coherently superposed in an interferometric setup formed by standing laser waves. As a result, the outgoing electron beam is separated into its spin components along the laser magnetic field, which is shown by both analytical and numerical solutions of Pauli's equation. The proposed laser field configuration thus exerts the same effect on free electrons like an ordinary Stern-Gerlach magnet does on atoms.
Growth and Electronic Structure of Heusler Compounds for Use in Electron Spin Based Devices
2015-06-01
Tyler Rhodes and Thomas Neulinger through the Center for Energy Efficient Materials Internship Program, 2012-2013 Teaching assistant for Semiconductor...will follow. The ensemble of electron spins can interact with the nuclear spins in the GaAs crystal through hyperfine interactions. The sign of the...magnetic field, P is the electron spin and bn is a nuclear field coefficient on the order of a few Tesla with a negative sign for GaAs.[59–61]. By
Silicon quantum processor with robust long-distance qubit couplings
Rahman, Rajib [Purdue University; Tosi, Guilherme [Centre for Quantum Computation and Communication Technology; Schmitt, Vivien [Centre for Quantum Computation and Communication Technology; Klimeck, Gerhard [Purdue University; Tenberg, Stefanie B. [Centre for Quantum Computation and Communication Technology; Morello, Andrea [Centre for Quantum Computation and Communication Technology; Mohiyaddin, Fahd A. [ORNL
2017-09-01
Practical quantum computers require a large network of highly coherent qubits, interconnected in a design robust against errors. Donor spins in silicon provide state-of-the-art coherence and quantum gate fidelities, in a platform adapted from industrial semiconductor processing. Here we present a scalable design for a silicon quantum processor that does not require precise donor placement and leaves ample space for the routing of interconnects and readout devices. We introduce the flip-flop qubit, a combination of the electron-nuclear spin states of a phosphorus donor that can be controlled by microwave electric fields. Two-qubit gates exploit a second-order electric dipole-dipole interaction, allowing selective coupling beyond the nearest-neighbor, at separations of hundreds of nanometers, while microwave resonators can extend the entanglement to macroscopic distances. We predict gate fidelities within fault-tolerance thresholds using realistic noise models. This design provides a realizable blueprint for scalable spin-based quantum computers in silicon.
Optically oriented electron spin transmission across ferromagnet/semiconductor interfaces
Taniyama, T.; Suzuki, I.; Wada, E.; Shirahata, Y.; Naito, T.; Itoh, M.; Yamaguchi, M.
2011-10-01
Electron spin transmission across ferromagnetic metal/semiconductor interfaces with different ferromagnetic contacts, i.e., Fe and FeGa, is studied using optical spin orientation method. The bias dependence of spin dependent photocurrent, which is the difference between the photocurrents excited with left- and right- handed circularly polarized lights, is found to show a dip-like feature at -0.058 and 0.021 V for Fe and FeGa contacts, respectively. The origin of the bias dependence of the spin dependent photocurrent is discussed on the basis of the Breit-Wigner type resonant tunneling process via interface resonant states, comparing the results for the both contacts. The results also indicate that the control of interface states is crucial to achieve efficient spin filtering effect at the ferromagnet/semiconductor interfaces.
Frenkel electron and a spinning body in a curved background
Ramírez, Walberto Guzmán [Depto. de Matemática, ICE,Universidade Federal de Juiz de Fora, São Pedro, MG (Brazil); Deriglazov, Alexei A. [Depto. de Matemática, ICE,Universidade Federal de Juiz de Fora, São Pedro, MG (Brazil); Laboratory of Mathematical Physics, Tomsk Polytechnic University,634050 Tomsk, Lenin Ave. 30 (Russian Federation); Pupasov-Maksimov, Andrey M. [Depto. de Matemática, ICE,Universidade Federal de Juiz de Fora, São Pedro, MG (Brazil)
2014-03-24
We develop a variational formulation of a particle with spin in a curved space-time background. The model is based on a singular Lagrangian which provides equations of motion, a fixed value of spin and Frenkel condition on spin-tensor. Comparing our equations with those of Papapetrou we conclude that the Frenkel electron in a gravitational field has the same behavior as a rotating body in the pole-dipole and leading-spin approximation. Due to constraints presented in the formulation, position space is endowed with a noncommutative structure induced by the spin of the particle. Therefore, the model provides a physically interesting example of a noncommutative particle in a curved background.
Electron Spin Pairing in High-Tc Superconductors
郭卫; 韩汝珊
2001-01-01
An electron pairing theory based on effective electron spin coupling mediated by antiferromagnetically correlated local moments is presented to account for high-Tc phenomena. We show that Kondo scattering and the suppression of the antiferromagnetic superexchange between Cu2+ moments lead to local triplet pairing, the mechanism underlying high-Tc superconductivity.
Electron spin and charge in semiconductor quantum dots
Elzerman, J.M.
2004-01-01
In this thesis, the spin and charge degree of freedom of electrons in semiconductor lateral and vertical quantum dots are experimentally investigated. The lateral quantum dot devices are defined in a two-dimensional electron gas (2DEG) below the surface of a GaAs/AlGaAs heterostructure, by metallic
Electron Spin Resonance at the Level of 1 04 Spins Using Low Impedance Superconducting Resonators
Eichler, C.; Sigillito, A. J.; Lyon, S. A.; Petta, J. R.
2017-01-01
We report on electron spin resonance measurements of phosphorus donors localized in a 200 μ m2 area below the inductive wire of a lumped element superconducting resonator. By combining quantum limited parametric amplification with a low impedance microwave resonator design, we are able to detect around 2 ×1 04 spins with a signal-to-noise ratio of 1 in a single shot. The 150 Hz coupling strength between the resonator field and individual spins is significantly larger than the 1-10 Hz coupling rates obtained with typical coplanar waveguide resonator designs. Because of the larger coupling rate, we find that spin relaxation is dominated by radiative decay into the resonator and dependent upon the spin-resonator detuning, as predicted by Purcell.
A fast "hybrid" silicon double quantum dot qubit
Shi, Zhan; Prance, J R; Gamble, John King; Koh, Teck Seng; Shim, Yun-Pil; Hu, Xuedong; Savage, D E; Lagally, M G; Eriksson, M A; Friesen, Mark; Coppersmith, S N
2011-01-01
We propose a quantum dot qubit architecture that has an attractive combination of speed and fabrication simplicity. It consists of a double quantum dot with one electron in one dot and two electrons in the other. The qubit itself is a set of two states with total spin quantum numbers $S^2=3/4$ ($S=\\half$) and $S_z = -\\half$, with the two different states being singlet and triplet in the doubly occupied dot. The architecture is relatively simple to fabricate, a universal set of fast operations can be implemented electrically, and the system has potentially long decoherence times. These are all extremely attractive properties for use in quantum information processing devices.
Spectroscopy of a Synthetic Trapped Ion Qubit
Hucul, David; Christensen, Justin E.; Hudson, Eric R.; Campbell, Wesley C.
2017-09-01
133Ba+ has been identified as an attractive ion for quantum information processing due to the unique combination of its spin-1 /2 nucleus and visible wavelength electronic transitions. Using a microgram source of radioactive material, we trap and laser cool the synthetic A =133 radioisotope of barium II in a radio-frequency ion trap. Using the same, single trapped atom, we measure the isotope shifts and hyperfine structure of the 62P1 /2↔62S1 /2 and 62P1 /2↔52D3 /2 electronic transitions that are needed for laser cooling, state preparation, and state detection of the clock-state hyperfine and optical qubits. We also report the 62P1 /2↔52D3 /2 electronic transition isotope shift for the rare A =130 and 132 barium nuclides, completing the spectroscopic characterization necessary for laser cooling all long-lived barium II isotopes.
Polarisation singularities in photonic crystals for an on-chip spin-photon interface
Beggs, Daryl M.; Young, Andrew B.; Thijssen, Arthur C. T.; Oulton, Ruth
2015-03-01
Integrated quantum photonic chips are a leading contender for future quantum technologies, which aim to use the entanglement and superposition properties of quantum physics to speed up the manipulation of data. Quantum information may be stored and transmitted in photons, which make excellent flying qubits. Photons suffer little from decoherence, and single qubit gates performed by changing photon phase, are straightforward. Less straightforward is the ability to create two qubit gates, where one photon is used to switch another's state; inherently difficult due to the extremely small interaction cross-section between photons. The required deterministic two-qubit interactions will likely need a hybrid scheme with the ``flying'' photonic qubit interacting with a ``static'' matter qubit. Here we present the design of a photonic crystal waveguide structure that can couple electron-spin to photon path, thus providing an interface between a static and a flying qubit. We will show that the complex polarization properties inherent in the photonic crystal eigenmodes supports polarization singularities - positions in the electric field vector where one of the parameters describing the local polarization ellipse is singular - and that these singularities are ideal for a range of quantum information applications. In particular, we will show that by placing a quantum dot at one of these singularities, the electron-spin becomes correlated with the photon emission direction, creating an in-plane spin-photon interface that can transfer quantum information from static to flying qubits.
Electron-Spin Filters Based on the Rashba Effect
Ting, David Z.-Y.; Cartoixa, Xavier; McGill, Thomas C.; Moon, Jeong S.; Chow, David H.; Schulman, Joel N.; Smith, Darryl L.
2004-01-01
Semiconductor electron-spin filters of a proposed type would be based on the Rashba effect, which is described briefly below. Electron-spin filters more precisely, sources of spin-polarized electron currents have been sought for research on, and development of, the emerging technological discipline of spintronics (spin-based electronics). There have been a number of successful demonstrations of injection of spin-polarized electrons from diluted magnetic semiconductors and from ferromagnetic metals into nonmagnetic semiconductors. In contrast, a device according to the proposal would be made from nonmagnetic semiconductor materials and would function without an applied magnetic field. The Rashba effect, named after one of its discoverers, is an energy splitting, of what would otherwise be degenerate quantum states, caused by a spin-orbit interaction in conjunction with a structural-inversion asymmetry in the presence of interfacial electric fields in a semiconductor heterostructure. The magnitude of the energy split is proportional to the electron wave number. The present proposal evolved from recent theoretical studies that suggested the possibility of devices in which electron energy states would be split by the Rashba effect and spin-polarized currents would be extracted by resonant quantum-mechanical tunneling. Accordingly, a device according to the proposal would be denoted an asymmetric resonant interband tunneling diode [a-RITD]. An a-RITD could be implemented in a variety of forms, the form favored in the proposal being a double-barrier heterostructure containing an asymmetric quantum well. It is envisioned that a-RITDs would be designed and fabricated in the InAs/GaSb/AlSb material system for several reasons: Heterostructures in this material system are strong candidates for pronounced Rashba spin splitting because InAs and GaSb exhibit large spin-orbit interactions and because both InAs and GaSb would be available for the construction of highly asymmetric
Tuning Electron Spin States in Quantum Dots by Spin-Orbit Interactions
LIU Yu; CHENG Fang
2011-01-01
@@ We theoretically investigate the influence of both Rashba spin-orbit interaction (RSOI) and Dresselhaus spin- orbit interaction (DSOI) on electron spin states, electron distribution and the optical absorption of a quantum dot.Our theoretical results show that the interplay between RSOI and DSOI results in an effective periodic potential, which consequently breaks the rotational symmetry and makes the quantum dot behave like two laterally coupled quantum dots.In the presence of RSOI and/or DSOI the spin is no longer a conserved quantity and its magnitude can be tuned by changing the strength of RSOI and/or DSOI.By reversing the direction of the perpendicular electric field, we can rotate the spatial distribution.This property provides us with a new way to control quantum states in a quantum dot by electrical means.
Dhas, M. Kumara; Benial, A. Milton Franklin, E-mail: miltonfranklin@yahoo.com [Department of Physics, NMSSVN College, Nagamalai, Madurai-625019, Tamilnadu (India); Jawahar, A. [Department of Chemistry, NMSSVN College, Nagamalai, Madurai-625019, Tamilnadu (India)
2014-04-24
The Electron spin resonance studies on the reduction process of nitroxyl spin probes were carried out for 1mM {sup 14}N labeled nitroxyl radicals in pure water and 1 mM concentration of ascorbic acid as a function of time. The electron spin resonance parameters such as signal intensity ratio, line width, g-value, hyperfine coupling constant and rotational correlation time were determined. The half life time was estimated for 1mM {sup 14}N labeled nitroxyl radicals in 1 mM concentration of ascorbic acid. The ESR study reveals that the TEMPONE has narrowest line width and fast tumbling motion compared with TEMPO and TEMPOL. From the results, TEMPONE has long half life time and high stability compared with TEMPO and TEMPOL radical. Therefore, this study reveals that the TEMPONE radical can act as a good redox sensitive spin probe for molecular imaging.
Foucault's Pendulum, Analog for an Electron Spin State
Linck, Rebecca
2012-11-01
The classical Lagrangian that describes the coupled oscillations of Foucault's pendulum presents an interesting analog to an electron's spin state in an external magnetic field. With a simple modification, this classical Lagrangian yields equations of motion that directly map onto the Schrodinger-Pauli Equation. This analog goes well beyond the geometric phase, reproducing a broad range of behavior from Zeeman-like frequency splitting to precession of the spin state. By demonstrating that unmeasured spin states can be fully described in classical terms, this research opens the door to using the tools of classical physics to examine an inherently quantum phenomenon.
Electronic spin state of iron in lower mantle perovskite.
Li, Jie; Struzhkin, Viktor V; Mao, Ho-Kwang; Shu, Jinfu; Hemley, Russell J; Fei, Yingwei; Mysen, Bjorn; Dera, Przemek; Prakapenka, Vitali; Shen, Guoyin
2004-09-28
The electronic spin state of iron in lower mantle perovskite is one of the fundamental parameters that governs the physics and chemistry of the most voluminous and massive shell in the Earth. We present experimental evidence for spin-pairing transition in aluminum-bearing silicate perovskite (Mg,Fe)(Si,Al)O(3) under the lower mantle pressures. Our results demonstrate that as pressure increases, iron in perovskite transforms gradually from the initial high-spin state toward the final low-spin state. At 100 GPa, both aluminum-free and aluminum-bearing samples exhibit a mixed spin state. The residual magnetic moment in the aluminum-bearing perovskite is significantly higher than that in its aluminum-free counterpart. The observed spin evolution with pressure can be explained by the presence of multiple iron species and the occurrence of partial spin-paring transitions in the perovskite. Pressure-induced spin-pairing transitions in the perovskite would have important bearing on the magnetic, thermoelastic, and transport properties of the lower mantle, and on the distribution of iron in the Earth's interior.
Strong mechanical driving of a single electron spin
Barfuss, A.; Teissier, J.; Neu, E.; Nunnenkamp, A.; Maletinsky, P.
2015-10-01
Quantum devices for sensing and computing applications require coherent quantum systems, which can be manipulated in fast and robust ways. Such quantum control is typically achieved using external electromagnetic fields, which drive the system’s orbital, charge or spin degrees of freedom. However, most existing approaches require complex and unwieldy gate structures, and with few exceptions are limited to the regime of weak coherent driving. Here, we present a novel approach to coherently drive a single electronic spin using internal strain fields in an integrated quantum device. Specifically, we employ time-varying strain in a diamond cantilever to induce long-lasting, coherent oscillations of an embedded nitrogen-vacancy (NV) centre spin. We perform direct spectroscopy of the phonon-dressed states emerging from this drive and observe hallmarks of the sought-after strong-driving regime, where the spin rotation frequency exceeds the spin splitting. Furthermore, we employ our continuous strain driving to significantly enhance the NV’s spin coherence time. Our room-temperature experiments thereby constitute an important step towards strain-driven, integrated quantum devices and open new perspectives to investigate unexplored regimes of strongly driven multilevel systems and exotic spin dynamics in hybrid spin-oscillator devices.
Sablikov, Vladimir A.; Shchamkhalova, Bagun S.
2014-05-01
We study the formation of spontaneous spin polarization in inhomogeneous electron systems with pair interaction localized in a small region that is not separated by a barrier from surrounding gas of non-interacting electrons. Such a system is interesting as a minimal model of a quantum point contact in which the electron-electron interaction is strong in a small constriction coupled to electron reservoirs without barriers. Based on the analysis of the grand potential within the self-consistent field approximation, we find that the formation of the polarized state strongly differs from the Bloch or Stoner transition in homogeneous interacting systems. The main difference is that a metastable state appears in the critical point in addition to the globally stable state, so that when the interaction parameter exceeds a critical value, two states coexist. One state has spin polarization and the other is unpolarized. Another feature is that the spin polarization increases continuously with the interaction parameter and has a square-root singularity in the critical point. We study the critical conditions and the grand potentials of the polarized and unpolarized states for one-dimensional and two-dimensional models in the case of extremely small size of the interaction region.
Shen, SQ; Ma, X.; Hu, L.; R. Tao
2004-01-01
In a two-dimensional electron gas with Rashba spin-orbit coupling, the external electric field may cause a spin Hall current in the direction perpendicular to the electric field. This effect was called the intrinsic spin Hall effect. In this paper, we investigate the influences of spin accumulation on this intrinsic spin Hall effect. We show that due to the existence of boundaries in a real sample, the spin Hall current generated by the intrinsic spin Hall effect will cause spin accumulation ...
Electrical Control, Read-out and Initialization of Single Electron Spins
Shafiei, M.
2013-01-01
An electron, in addition to its electric charge, possesses a small magnetic moment, called spin. The spin of an electron can point parallel (spin-up) or antiparallel (spin-down) to the magnetic field. These two states are analogous to zero and one of the logical bit in current digital electronic dev
Qubit Decoherence and Non-Markovian Dynamics at Low Temperatures via an Effective Spin-Boson Model
Shiokawa, K
2004-01-01
Quantum Brownian oscillator model (QBM), in the Fock-space representation, can be viewed as a multi-level spin-boson model. At sufficiently low temperature, the oscillator degrees of freedom are dynamically reduced to the lowest two levels and the system behaves effectively as a two-level (E2L) spin-boson model (SBM) in this limit. We discuss the physical mechanism of level reduction and analyze the behavior of E2L-SBM from the QBM solutions. The availability of close solutions for the QBM enables us to study the non-Markovian features of decoherence and leakage in a SBM in the non-perturbative regime (e.g. without invoking the Born approximation) in better details than before. Our result captures very well the characteristic non-Markovian short time low temperature behavior common in many models.
Simulating electron spin entanglement in a double quantum dot
Rodriguez-Moreno, M. A.; Hernandez de La Luz, A. D.; Meza-Montes, Lilia
2011-03-01
One of the biggest advantages of having a working quantum-computing device when compared with a classical one, is the exponential speedup of calculations. This exponential increase is based on the ability of a quantum system to create and operate on entangled states. In order to study theoretically the entanglement between two electron spins, we simulate the dynamics of two electron spins in an electrostatically-defined double quantum dot with a finite barrier height between the dots. Electrons are initially confined to separated quantum dots. Barrier height is varied and the spin entanglement as a function of this variation is investigated. The evolution of the system is simulated by using a numerical approach for solving the time-dependent Schrödinger equation for two particles. Partially supported by VIEP-BUAP.
Controlled Phase Gate Based on an Electron Floating on Helium
SHI Yan-Li; MEI Feng; YU Ya-Fei; ZHANG Zhi-Ming
2011-01-01
We propose a scheme to generate the controlled phase gate by using an electron floating on liquid helium. The electron is also driven by a classical laser beam and by an oscillating magnetic field. In the process, the vibration of the electron is used as the qubus to couple the energy level qubit (1D Stark-shifted hydrogen) and spin qubit Ultimately. the controlled phase gate can be generated.%@@ We propose a scheme to generate the controlled phase gate by using an electron floating on liquid helium.The electron is also driven by a classical laser beam and by an oscillating magnetic field.In the process,the vibration of the electron is used as the qubus to couple the energy level qubit(1D Stark-shifted hydrogen) and spin qubit.Ultimately,the controlled phase gate can be generated.
Spin-valley splitting of electron beam in graphene
Yu Song
2016-11-01
Full Text Available We study spatial separation of the four degenerate spin-valley components of an electron beam in a EuO-induced and top-gated ferromagnetic/pristine/strained graphene structure. We show that, in a full resonant tunneling regime for all beam components, the formation of standing waves can lead sudden phase jumps ∼−π and giant lateral Goos-Hänchen shifts as large as the transverse beam width, while the interplay of the spin and valley imaginary wave vectors in the modulated regions can lead differences of resonant angles for the four spin-valley flavors, manifesting a spin-valley beam splitting effect. The splitting effect is found to be controllable by the gating and strain.
All-optical control of a solid-state spin using coherent dark states
Yale, Christopher G; Christle, David J; Burkard, Guido; Heremans, F Joseph; Bassett, Lee C; Awschalom, David D
2013-01-01
The study of individual quantum systems in solids, for use as quantum bits (qubits) and probes of decoherence, requires protocols for their initialization, unitary manipulation, and readout. In many solid-state quantum systems, these operations rely on disparate techniques that can vary widely depending on the particular qubit structure. One such qubit, the nitrogen-vacancy (NV) center spin in diamond, can be initialized and read out through its special spin selective intersystem crossing, while microwave electron spin resonance (ESR) techniques provide unitary spin rotations. Instead, we demonstrate an alternative, fully optical approach to these control protocols in an NV center that does not rely on its intersystem crossing. By tuning an NV center to an excited-state spin anticrossing at cryogenic temperatures, we use coherent population trapping and stimulated Raman techniques to realize initialization, readout, and unitary manipulation of a single spin. Each of these techniques can be directly performed ...
Field theory of the spinning electron: I - Internal motions
Salesi, Giovanni [Universita Statale di Catania (Italy). Dipt. di Fisica; Recami, Erasmo [Universita Statale di Bergamo, Dalmine, BG (Italy). Facolta di Ingegneria]|[Universidade Estadual de Campinas, SP (Brazil). Dept. de Matematica Aplicada
1994-05-01
One of the most satisfactory picture of spinning particles is the Barut-Zanghi (BZ) classical theory for the relativistic electron, that relates the electron spin with the so-called Zitterbewegung (zbw). The BZ theory has been recently studied in the Lagrangian and Hamiltonian symplectic formulations, both in flat and in curved space-time. The BZ motion equations constituted the starting point for two recent works about spin and electron structure, co-authored by us, which adopted the Clifford algebra formalism. In this letter, by employing on the contrary the ordinary tensorial language, we first write down a meaningful (real) equation of motion, describing particle classical paths, quite different from the corresponding (complex) equation of the standard Dirac theory. As a consequence, we succeed in regarding the electron as an extended-type object with a classically intelligible structure (thus overcoming some long-standing, well-known problems). Second, we make explicit the kinematical properties of the 4-velocity field v{sup {mu}}, which also result to be quite different from the ordinary ones, valid for scalar particles. At last, we analyze the inner zbw motions, both time-like and light-like, as functions of the initial conditions (in particular, for the case of classical uniform motions, the z component of spin s is shown to be quantized). In so doing, we make explicit the strict correlation existing between electron polarization and zbw kinematics. (author). 9 refs.
Wencka, M.; Lijewski, S.; Hoffmann, S. K.
2008-06-01
ESR spectra were recorded in the X-band (9.6 GHz) and in the W-band (94 GHz) and electron spin relaxation was measured by electron spin echo (ESE) in the temperature range 4.2-300 K for radicals in natural calcite samples obtained from a cave stalactite and a dripstone layer. Four types of carbonate radical spectra and two sulfate radical spectra were identified and high accuracy g-factors were derived. Time and temperature behaviour of the spectra show that the dominating CO2- radicals are rigidly bonded or undergo free reorientations, whereas CO3-, SO2- and SO3- only undergo free reorientations. Below 200 K the free reorientations of CO2- are suppressed and a hindered rotation around single local axis appears. The ESE detected spectrum proves that the lines of free rotating radicals are homogeneously broadened, thus they cannot participate in electron spin echo formation. Spin-lattice relaxation data show that CO2- radicals are decoupled from lattice phonons and relax via local mode tunnelling motion between inequivalent oxygen positions of CO2- molecules. The tunnelling appears in two excited vibrational states of energy 71 and 138 cm-1. Librational motions of CO2- molecules were detected by electron spin echo decay (phase relaxation) with energy 153 cm-1. Two kinds of impurity hydrogen atoms were distinguished from ESEEM: in-water inclusions and water coordinated to the calcium ions.
Electron spin resonance in a two-dimensional Fermi liquid with spin-orbit coupling
Maiti, Saurabh; Imran, Muhammad; Maslov, Dmitrii L.
2016-01-01
Electron spin resonance (ESR) is usually viewed as a single-particle phenomenon protected from the effect of many-body correlations. We show that this is not the case in a two-dimensional Fermi liquid (FL) with spin-orbit coupling (SOC). Depending on whether the in-plane magnetic field is below or above some critical value, ESR in such a system probes up to three chiral-spin collective modes, augmented by the spin mode in the presence of the field, or the Silin-Leggett mode. All the modes are affected by both SOC and FL renormalizations. We argue that ESR can be used as a probe not only for SOC but also for many-body physics.
Sample heating system for spin-polarized scanning electron microscopy.
Kohashi, Teruo; Motai, Kumi
2013-08-01
A sample-heating system for spin-polarized scanning electron microscopy (spin SEM) has been developed and used for microscopic magnetization analysis at temperatures up to 500°C. In this system, a compact ceramic heater and a preheating operation keep the ultra-high vacuum conditions while the sample is heated during spin SEM measurement. Moreover, the secondary-electron collector, which is arranged close to the sample, was modified so that it is not damaged at high temperatures. The system was used to heat a Co(1000) single-crystal sample from room temperature up to 500°C, and the magnetic-domain structures were observed. Changes of the domain structures were observed around 220 and 400°C, and these changes are considered to be due to phase transitions of this sample.
Fidelity enhancement by logical qubit encoding.
Henry, Michael K; Ramanathan, Chandrasekhar; Hodges, Jonathan S; Ryan, Colm A; Ditty, Michael J; Laflamme, Raymond; Cory, David G
2007-11-30
We demonstrate coherent control of two logical qubits encoded in a decoherence free subspace (DFS) of four dipolar-coupled protons in an NMR quantum information processor. A pseudopure fiducial state is created in the DFS, and a unitary logical qubit entangling operator evolves the system to a logical Bell state. The four-spin molecule is partially aligned by a liquid crystal solvent, which introduces strong dipolar couplings among the spins. Although the system Hamiltonian is never fully specified, we demonstrate high fidelity control over the logical degrees of freedom. In fact, the DFS encoding leads to higher fidelity control than is available in the full four-spin Hilbert space.
Coherence and control of a single electron spin in a quantum dot
Koppens, F.H.L.
2007-01-01
An electron does not only have an electric charge, but also a small magnetic moment, called spin. In a magnetic field, the spin can point in the same direction as the field (spin-up) or in the opposite direction (spin-down). However, the laws of quantum mechanics also allow the spin to exist in both
Electronic spin susceptibility of metallic superconductive nano-particles
Li Feng; Chen Zhi-Qian; Li Qing
2006-01-01
We have observed the thermodynamic properties of metallic superconductive nano-particles in the grand canonical ensemble; and the level distribution and the level correlation between the discrete electronic energy levels are considered in the calculation of the electronic spin susceptibility of the ensemble numerically. The quantum effect, even-odd effect and other special effects existing in the metallic nano-particles are also studied in this article.
Uniform spinning sampling gradient electron paramagnetic resonance imaging.
Johnson, David H; Ahmad, Rizwan; Liu, Yangping; Chen, Zhiyu; Samouilov, Alexandre; Zweier, Jay L
2014-02-01
To improve the quality and speed of electron paramagnetic resonance imaging (EPRI) acquisition by combining a uniform sampling distribution with spinning gradient acquisition. A uniform sampling distribution was derived for spinning gradient EPRI acquisition (uniform spinning sampling, USS) and compared to the existing (equilinear spinning sampling, ESS) acquisition strategy. Novel corrections were introduced to reduce artifacts in experimental data. Simulations demonstrated that USS puts an equal number of projections near each axis whereas ESS puts excessive projections at one axis, wasting acquisition time. Artifact corrections added to the magnetic gradient waveforms reduced noise and correlation between projections. USS images had higher SNR (85.9 ± 0.8 vs. 56.2 ± 0.8) and lower mean-squared error than ESS images. The quality of the USS images did not vary with the magnetic gradient orientation, in contrast to ESS images. The quality of rat heart images was improved using USS compared to that with ESS or traditional fast-scan acquisitions. A novel EPRI acquisition which combines spinning gradient acquisition with a uniform sampling distribution was developed. This USS spinning gradient acquisition offers superior SNR and reduced artifacts compared to prior methods enabling potential improvements in speed and quality of EPR imaging in biological applications. Copyright © 2013 Wiley Periodicals, Inc.
Electron spin coherence and electron nuclear double resonance of Bi donors in natural Si.
George, Richard E; Witzel, Wayne; Riemann, H; Abrosimov, N V; Nötzel, N; Thewalt, Mike L W; Morton, John J L
2010-08-06
Donors in silicon hold considerable promise for emerging quantum technologies, due to their uniquely long electron spin coherence times. Bismuth donors in silicon differ from more widely studied group V donors, such as phosphorous, in several significant respects: They have the strongest binding energy (70.98 meV), a large nuclear spin (I=9/2), and a strong hyperfine coupling constant (A=1475.4 MHz). These larger energy scales allow us to perform a detailed test of theoretical models describing the spectral diffusion mechanism that is known to govern the electron spin decoherence of P donors in natural silicon. We report the electron-nuclear double resonance spectra of the Bi donor, across the range 200 MHz to 1.4 GHz, and confirm that coherence transfer is possible between electron and nuclear spin degrees of freedom at these higher frequencies.
Hu, H; Hu, Huping; Wu, Maoxin
2002-01-01
We postulate that consciousness is connected to quantum mechanical spin since said spin is embedded in the microscopic structure of spacetime and may be more fundamental than spacetime itself. Thus, we theorize that consciousness is connected with the fabric of spacetime through spin. That is, spin is the "pixel" and "antenna" of mind. The unity of mind is achieved by non-local means within the pre-spacetime domain interfaced with spacetime. Human mind is possible because of the particular structures and dynamics of our brain postulated working as follows: The unpaired electronic spins of highly lipid-soluble and rapidly diffusing oxygen molecules extract information from the dynamical neural membranes and communicate said information through strong spin-spin couplings to the nuclear spin ensemble in the membranes for consciousness-related quantum statistical processing which survives decoherence. In turn, the dynamics of the nuclear spin ensemble has effects through spin chemistry on the classical neural act...
Quantum logic processor: Implementation with electronic Mach-Zehnder interferometer
Sarkar, Angik; Bhattacharyya, T. K.; Patwardhan, Ajay
2006-05-01
An approach for implementation of quantum logic in electronic Mach-Zehnder interferometer (MZI) has been described in this letter. All single qubit gates can be achieved by electron spin manipulation using Rashba spin-orbit coupling. Double qubit gates can also be implemented using the orbital degree of freedom of the electron. The MZI can be realized with intertwined ballistic nanowires. Spin injection and detection in the system can be done by a mesoscopic Stern-Gerlach apparatus. The system can be coupled in an array to form the quantum logic processor.
Park, Seongjun; Srivastava, Deepak; Cho, Kyeongjae; Biegel, Bryan (Technical Monitor)
2001-01-01
Models of encapsulated 1/2 nuclear spin H-1 and P-31 atoms in fullerene and diamond nanocrystallite, respectively, are proposed and examined with ab-initio local density functional method for possible applications as single quantum bits (qubits) in solid-state quantum computers. A H-1 atom encapsulated in a fully deuterated fullerene, C(sub 20)D(sub 20), forms the first model system and ab-initio calculation shows that H-1 atom is stable in atomic state at the center of the fullerene with a barrier of about 1 eV to escape. A P-31 atom positioned at the center of a diamond nanocrystallite is the second model system, and 3 1P atom is found to be stable at the substitutional site relative to interstitial sites by 15 eV, Vacancy formation energy is 6 eV in diamond so that substitutional P-31 atom will be stable against diffusion during the formation mechanisms within the nanocrystallite. The coupling between the nuclear spin and weakly bound (valance) donor electron coupling in both systems is found to be suitable for single qubit applications, where as the spatial distributions of (valance) donor electron wave functions are found to be preferentially spread along certain lattice directions facilitating two or more qubit applications. The feasibility of the fabrication pathways for both model solid-state qubit systems within practical quantum computers is discussed with in the context of our proposed solid-state qubits.
Classical Emulation of a Two-Qubit Quantum Computer with Analog Electronics
La Cour, Brian; Ostrove, Corey; Ott, Granville; Starkey, Michael; Wilson, Gary
Abstract: The Hilbert space mathematical structure of a gate-based quantum computer may be reproduced by mapping the computational basis states to corresponding functions in the space of complex exponentials and identifying an inner product between any two such functions. The span of these complex basis exponentials may then identified with the finite-dimensional Hilbert space of a gate-based quantum computer. By using classical analog electronic components, such as four-quadrant multipliers and operational amplifiers, voltage signals representing arbitrary four-dimensional quantum states, along with the equivalent gate and measurement operations of a quantum computer have been physically realized through the corresponding circuitry. The fidelity of the emulation is measured using both a direct evaluation of the signal as well as through an emulation of quantum state tomography to infer the quantum state. We demonstrate that for both state synthesis and gate operations, our quantum emulation device is capable of achieving over 99% fidelity. This work was supported by the Office of Naval Research under Grant No. N00014-14-1-0323.
Quantum control and process tomography of a semiconductor quantum dot hybrid qubit.
Kim, Dohun; Shi, Zhan; Simmons, C B; Ward, D R; Prance, J R; Koh, Teck Seng; Gamble, John King; Savage, D E; Lagally, M G; Friesen, Mark; Coppersmith, S N; Eriksson, Mark A
2014-07-03
The similarities between gated quantum dots and the transistors in modern microelectronics--in fabrication methods, physical structure and voltage scales for manipulation--have led to great interest in the development of quantum bits (qubits) in semiconductor quantum dots. Although quantum dot spin qubits have demonstrated long coherence times, their manipulation is often slower than desired for important future applications, such as factoring. Furthermore, scalability and manufacturability are enhanced when qubits are as simple as possible. Previous work has increased the speed of spin qubit rotations by making use of integrated micromagnets, dynamic pumping of nuclear spins or the addition of a third quantum dot. Here we demonstrate a qubit that is a hybrid of spin and charge. It is simple, requiring neither nuclear-state preparation nor micromagnets. Unlike previous double-dot qubits, the hybrid qubit enables fast rotations about two axes of the Bloch sphere. We demonstrate full control on the Bloch sphere with π-rotation times of less than 100 picoseconds in two orthogonal directions, which is more than an order of magnitude faster than any other double-dot qubit. The speed arises from the qubit's charge-like characteristics, and its spin-like features result in resistance to decoherence over a wide range of gate voltages. We achieve full process tomography in our electrically controlled semiconductor quantum dot qubit, extracting high fidelities of 85 per cent for X rotations (transitions between qubit states) and 94 per cent for Z rotations (phase accumulation between qubit states).
Dynamical Decoupling of a single electron spin at room temperature
Naydenov, Boris; Hall, Liam T; Shin, Chang; Fedder, Helmut; Hollenberg, Lloyd C L; Jelezko, Fedor; Wrachtrup, Jörg
2010-01-01
Here we report the increase of the coherence time T$_2$ of a single electron spin at room temperature by using dynamical decoupling. We show that the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence can prolong the T$_2$ of a single Nitrogen-Vacancy center in diamond up to 2.44 ms compared to the Hahn echo measurement where T$_2 = 390~\\mu$s. Moreover, by performing spin locking experiments we demonstrate that with CPMG the maximum possible $T_2$ is reached. On the other hand, we do not observe strong increase of the coherence time in nanodiamonds, possibly due to the short spin lattice relaxation time $T_1=100~\\mu$s (compared to T$_1$ = 5.93 ms in bulk). An application for detecting low magnetic field is demonstrated, where we show that the sensitivity using the CPMG method is improved by about a factor of two compared to the Hahn echo method.
Surface spin-electron acoustic waves in magnetically ordered metals
Andreev, Pavel A
2015-01-01
Degenerate plasmas with motionless ions show existence of three surface waves: the Langmuir wave, the electromagnetic wave, and the zeroth sound. Applying the separated spin evolution quantum hydrodynamics to half-space plasma we demonstrate the existence of the surface spin-electron acoustic wave (SSEAW). We study dispersion of the SSEAW. We show that there is hybridization between the surface Langmuir wave and the SSEAW at rather small spin polarization. In the hybridization area the dispersion branches are located close to each other. In this area there is a strong interaction between these waves leading to the energy exchange. Consequently, generating the Langmuir waves with the frequencies close to hybridization area we can generate the SSEAWs. Thus, we report a method of creation of the SEAWs.
Electronic transport through EuO spin filter tunnel junctions
Jutong, Nuttachai; Eckern, Ulrich [Institut fuer Physik, Universitaet Augsburg, 86135 Augsburg (Germany); Rungger, Ivan; Sanvito, Stefano [School of Physics and CRANN, Trinity College Dublin, Dublin (Ireland); Schwingenschloegl, Udo [KAUST, PSE Division, Thuwal 23955-6900, Kingdom of Saudi Arabia (Saudi Arabia)
2012-07-01
Spin filter tunnel junctions based on europium monoxide (EuO), a ferromagnetic semiconductor, are investigated by means of density functional theory. In particular, the spin transport of Cu/EuO/Cu junctions is investigated by using the self-consistent ab-initio electron transport code SMEAGOL. The dependence of the transmission coefficient on the interface spacing and on the EuO thickness is studied, and explained in terms of the density of states and the complex band structure of EuO. Our calculation indicates that EuO epitaxially grown on Cu can act as a perfect spin filter, with polarization close to 100%, which is related mainly to the Eu-4f states. The transmission coefficient is sensitive to the interface spacing, since this spacing determines the charge transfer between EuO and the Cu leads.
Perfect Single Qubit Mirroring Effects on Two and Three Maximally Entangled Qubits
M.(A)vila
2013-01-01
Perfect quantum state mirroring in a chain of N spins is defined as the condition in which the state |i〉 of the chain is swapped into the state |N-i〉 within a time evolution interval τ.Such a phenomenon is an interesting way of transfering entanglement.An expressions for the perfect mirroring of a single qubit contained in a spin chain were proposed in the past.We exploit such an expressions for calculating the evolution times in chains of both two and three spins.In the case of a chain of two qubits,we derive conditions under which the associated four Bell states diagonalize the Hamiltonian.It is found that for the two Bell states |Φ+〉 and |Φ-〉,perfect mirroring does not occur (i.e.entanglement is not preserved under swapping).On the other hand,perfect single qubit mirror effect (entanglement preservation) indeed occurs for the other two Bell states |Ψ+〉 and |Ψ-〉 which are mapped into |Φ+〉 and |Φ-〉 respectively.For the case of a chain of three qubits,the effects of a perfect single qubit mirroring on a set of four maximally entangled three qubit states Ψ1,Ψ2,x1,and x2 are studied.Due to the fact that quantum mirroring preserves maximal entanglement,the states Ψ1and Ψ2 are not altered.However,quantum mirroring changes the states x1 and x2 only if we apply perfect quantum state mirroring in the site a =1 of the three qubits spin chain.The above constrains the preservation of maximal entanglement under qubit mirroring of such a state.Due to the fact that swapping has already been experimentally tested,a posible.experimental implementations of single qubit mirroring is possible.
Superconducting Qubits: A Short Review
Devoret, M. H.; Wallraff, A.; Martinis, J. M.
2004-01-01
Superconducting qubits are solid state electrical circuits fabricated using techniques borrowed from conventional integrated circuits. They are based on the Josephson tunnel junction, the only non-dissipative, strongly non-linear circuit element available at low temperature. In contrast to microscopic entities such as spins or atoms, they tend to be well coupled to other circuits, which make them appealling from the point of view of readout and gate implementation. Very recently, new designs ...
Reaching the quantum limit of sensitivity in electron spin resonance
Bienfait, A.; Pla, J. J.; Kubo, Y.; Stern, M.; Zhou, X.; Lo, C. C.; Weis, C. D.; Schenkel, T.; Thewalt, M. L. W.; Vion, D.; Esteve, D.; Julsgaard, B.; Mølmer, K.; Morton, J. J. L.; Bertet, P.
2016-03-01
The detection and characterization of paramagnetic species by electron spin resonance (ESR) spectroscopy is widely used throughout chemistry, biology and materials science, from in vivo imaging to distance measurements in spin-labelled proteins. ESR relies on the inductive detection of microwave signals emitted by the spins into a coupled microwave resonator during their Larmor precession. However, such signals can be very small, prohibiting the application of ESR at the nanoscale (for example, at the single-cell level or on individual nanoparticles). Here, using a Josephson parametric microwave amplifier combined with high-quality-factor superconducting microresonators cooled at millikelvin temperatures, we improve the state-of-the-art sensitivity of inductive ESR detection by nearly four orders of magnitude. We demonstrate the detection of 1,700 bismuth donor spins in silicon within a single Hahn echo with unit signal-to-noise ratio, reduced to 150 spins by averaging a single Carr-Purcell-Meiboom-Gill sequence. This unprecedented sensitivity reaches the limit set by quantum fluctuations of the electromagnetic field instead of thermal or technical noise, which constitutes a novel regime for magnetic resonance. The detection volume of our resonator is ˜0.02 nl, and our approach can be readily scaled down further to improve sensitivity, providing a new versatile toolbox for ESR at the nanoscale.
Frederiksen, Anne M; Festersen, Rikke M; Andersen, Mogens L
2008-09-24
An electron spin resonance (ESR)-based method was used for evaluating the levels of radical formation during mashing and in sweet wort. The method included the addition of 5% (v/v) ethanol together with the spin trap alpha-4-pyridyl(1-oxide)- N- tert-butylnitrone (POBN) to wort, followed by monitoring the rate of formation of POBN spin adducts during aerobic heating of the wort. The presence of ethanol makes the spin trapping method more selective and sensitive for the detection of highly reactive radicals such as hydroxyl and alkoxyl radicals. Samples of wort that were collected during the early stages of the mashing process gave higher rates of spin adduct formation than wort samples collected during the later stages. The lower oxidative stability of the early wort samples was confirmed by measuring the rate of oxygen consumption during heating of the wort. The addition of Fe(II) to the wort samples increased the rate of spin adduct formation, whereas the addition of Fe(II) during the mashing had no effect on the oxidative stability of the wort samples. Analysis of the iron content in the sweet wort samples demonstrated that iron added during the mashing had no effect on the iron level in the wort. The moderate temperatures during the early steps of mashing allow the endogenous malt enzymes to be active. The potential antioxidative effects of different redox-active enzymes during mashing were tested by measuring the rate of spin adduct formation in samples of wort. Surprisingly, a high catalase dosage caused a significant, 20% reduction of the initial rate of radical formation, whereas superoxide dismutase had no effect on the oxidation rates. This suggests that hydrogen peroxide and superoxide are not the only intermediates that play a role in the oxidative reactions occurring during aerobic oxidation of sweet wort.
MONTE CARLO SIMULATION OF SPIN-POLARIZED SECONDARY ELECTRONS FROM IRON
X. Sun; Z.J. Ding; H.M Li; K. Salma; Z.M. Zhang; W.S. Tan
2005-01-01
A Monte Carlo model considering the electron spin direction and spin asymmetry has been developed. The energy distribution of the secondary electron polarization and the primary energy dependence of the polarization from Fe are studied. The simulation results show that:(1) the intensity of the spin-up secondary electrons is larger thanvthat of thevspin-down secondary electrons, suggesting the secondary electrons are spin polarized; (2) the spin polarization of secondary electrons with nearly zero kinetic energy is higher than the average valance spin polarization, Pb=27% for Fe. With increasing kinetic energy, the spin polarization of the secondary electrons decreases to the value of Pb remaining constant at higher kinetic energies;(3) the spin polarization increases with an increase in the primary energy and reaches a saturation value at higher primary energy in both the Monte Carlo simulation and experimental results.
Inversion of electron spin resonance signal in coals
Poklonski, N. A.; Vyrko, S. A.; Poklonskaya, O. N.; Lapchuk, N. M.; Munkhtsetseg, S.
2013-07-01
Samples of coal from the Donetsk basin (carbon content ~90 mass%) in both lump and powder forms were studied by continuous-wave electron spin resonance (ESR) at room temperature in air. Inversion of the ESR signal (being in phase with modulation of the constant magnetic field) with an increase of lump size along the magnetic component of the microwave field was observed in the cavity of the radiospectrometer.
Nanoscale microwave imaging with a single electron spin in diamond
Appel, Patrick; Ganzhorn, Marc; Neu, Elke; Maletinsky, Patrick
2015-01-01
We report on imaging of microwave (MW) magnetic fields using a magnetometer based on the electron spin of a nitrogen vacancy center in diamond. We quantitatively image the magnetic field generated by high frequency (GHz) MW current with nanoscale resolution using a scanning probe technique. We demonstrate a MW magnetic field sensitivity in the range of a few nT/$\\sqrt{\\text{Hz}}$, polarization selection and broadband capabilities under ambient conditions and thereby establish the nitrogen vac...
Semiconductor adiabatic qubits
Carroll, Malcolm S.; Witzel, Wayne; Jacobson, Noah Tobias; Ganti, Anand; Landahl, Andrew J.; Lilly, Michael; Nguyen, Khoi Thi; Bishop, Nathaniel; Carr, Stephen M.; Bussmann, Ezra; Nielsen, Erik; Levy, James Ewers; Blume-Kohout, Robin J.; Rahman, Rajib
2016-12-27
A quantum computing device that includes a plurality of semiconductor adiabatic qubits is described herein. The qubits are programmed with local biases and coupling terms between qubits that represent a problem of interest. The qubits are initialized by way of a tuneable parameter, a local tunnel coupling within each qubit, such that the qubits remain in a ground energy state, and that initial state is represented by the qubits being in a superposition of |0> and |1> states. The parameter is altered over time adiabatically or such that relaxation mechanisms maintain a large fraction of ground state occupation through decreasing the tunnel coupling barrier within each qubit with the appropriate schedule. The final state when tunnel coupling is effectively zero represents the solution state to the problem represented in the |0> and |1> basis, which can be accurately read at each qubit location.
Spin-orbit-induced strong coupling of a single spin to a nanomechanical resonator
Palyi, Andras [University of Konstanz (Germany); Eoetvoes University, Budapest (Hungary); Struck, Philipp R.; Burkard, Guido [University of Konstanz (Germany); Rudner, Mark [Harvard University, Cambridge, Massachusetts (United States); Flensberg, Karsten [Harvard University, Cambridge, Massachusetts (United States); Niels Bohr Institute, Copenhagen (Denmark)
2012-07-01
We theoretically investigate the coupling of electron spin to vibrational motion due to curvature-induced spin-orbit coupling in suspended carbon nanotube quantum dots. Our estimates indicate that, with current capabilities, a quantum dot with an odd number of electrons can serve as a realization of the Jaynes-Cummings model of quantum electrodynamics in the strong-coupling regime. A quantized flexural mode of the suspended tube plays the role of the optical mode and we identify two distinct two-level subspaces, at small and large magnetic field, which can be used as qubits in this setup. The strong intrinsic spin-mechanical coupling allows for detection, as well as manipulation of the spin qubit, and may yield enhanced performance of nanotubes in sensing applications.
Fully robust qubit in atomic and molecular three-level systems
Aharon, N.; Cohen, I.; Jelezko, F.; Retzker, A.
2016-12-01
We present a new method of constructing a fully robust qubit in a three-level system. By the application of continuous driving fields, robustness to both external and controller noise is achieved. Specifically, magnetic noise and power fluctuations do not operate within the robust qubit subspace. Whereas all the continuous driving based constructions of such a fully robust qubit considered so far have required at least four levels, we show that in fact only three levels are necessary. This paves the way for simple constructions of a fully robust qubit in many atomic and solid state systems that are controlled by either microwave or optical fields. We focus on the NV-center in diamond and analyze the implementation of the scheme, by utilizing the electronic spin sub-levels of its ground state. In current state-of-the-art experimental setups the scheme leads to improvement of more than two orders of magnitude in coherence time, pushing it towards the lifetime limit. We show how the fully robust qubit can be used to implement quantum sensing, and in particular, the sensing of high frequency signals.
RKKY interaction for the spin-polarized electron gas
Valizadeh, Mohammad M.; Satpathy, Sashi
2015-11-01
We extend the original work of Ruderman, Kittel, Kasuya and Yosida (RKKY) on the interaction between two magnetic moments embedded in an electron gas to the case where the electron gas is spin-polarized. The broken symmetry of a host material introduces the Dzyaloshinsky-Moriya (DM) vector and tensor interaction terms, in addition to the standard RKKY term, so that the net interaction energy has the form ℋ = JS1 ṡS2 + D ṡS1 ×S2 + S1 ṡΓ ↔ṡS2. We find that for the spin-polarized electron gas, a nonzero tensor interaction Γ ↔ is present in addition to the scalar RKKY interaction J, while D is zero due to the presence of inversion symmetry. Explicit expressions for these are derived for the electron gas both in 2D and 3D and we show that the net magnetic interaction can be expressed as a sum of Heisenberg and Ising like terms. The RKKY interaction exhibits a beating pattern, caused by the presence of the two Fermi momenta kF↑ and kF↓, while the R-3 distance dependence of the original RKKY result for the 3D electron gas is retained. This model serves as a simple example of the magnetic interaction in systems with broken symmetry, which goes beyond the RKKY interaction.
Entanglement of mixed quantum states for qubits and qudit in double photoionization of atoms
Chakraborty, M., E-mail: bminakshi@yahoo.com [Department of Physics, Asansol Girls’ College, Asansol 713304 (India); Sen, S. [Department of Physics, Triveni Devi Bhalotia College, Raniganj 713347 (India)
2015-08-15
Highlights: • We study tripartite entanglement between two electronic qubits and an ionic qudit. • We study bipartite entanglement between any two subsystems of a tripartite system. • We have presented a quantitative application of entangled properties in Neon atom. - Abstract: Quantum entanglement and its paradoxical properties are genuine physical resources for various quantum information tasks like quantum teleportation, quantum cryptography, and quantum computer technology. The physical characteristic of the entanglement of quantum-mechanical states, both for pure and mixed, has been recognized as a central resource in various aspects of quantum information processing. In this article, we study the bipartite entanglement of one electronic qubit along with the ionic qudit and also entanglement between two electronic qubits. The tripartite entanglement properties also have been investigated between two electronic qubits and an ionic qudit. All these studies have been done for the single-step double photoionization from an atom following the absorption of a single photon without observing spin orbit interaction. The dimension of the Hilbert space of the qudit depends upon the electronic state of the residual photoion A{sup 2+}. In absence of SOI, when Russell–Saunders coupling (L–S coupling) is applicable, dimension of the qudit is equal to the spin multiplicity of A{sup 2+}. For estimations of entanglement and mixedness, we consider the Peres–Horodecki condition, concurrence, entanglement of formation, negativity, linear and von Neumann entropies. In case of L–S coupling, all the properties of a qubit–qudit system can be predicted merely with the knowledge of the spins of the target atom and the residual photoion.
The S-DALINAC polarized electron injector SPIN
Eckardt, Christian; Bonnes, Uwe; Brunken, Marco; Eichhorn, Ralf; Enders, Joachim; Espig, Martin; Fritzsche, Yuliya; Haas, Oliver; Ingenhaag, Christoph; Lindemann, Janina; Platz, Markus; Wagner, Markus; Weber, Antje; Zwicker, Benjamin [Institut fuer Kernphysik, Technische Universitaet Darmstadt (Germany); Aulenbacher, Kurt [Institut fuer Kernphysik, Johannes-Gutenberg-Universitaet Mainz (Germany)
2012-07-01
At the superconducting 130 MeV Darmstadt electron linac S-DALINAC a source of polarized electrons has been installed. Pulsed Ti:Sapphire and diode lasers illuminate a superlattice-GaAs cathode, producing polarized electrons preaccelerated to 100 keV. A Wien filter and Mott polarimeter are used for spin manipulation and polarization measurement. Downstream of the superconducting injector linac a 5-10 MeV Mott polarimeter has been installed. A Moeller polarimeter behind the main linac has been designed for energies between 50 and 130 MeV, and additional Compton-transmission polarimeters will be installed for online polarization monitoring. Photo-fission measurements of different uranium isotopes have been carried out and an active target setup is under investigation. We report on the status and performance of the source of polarized electrons and currently planned experiments with polarized beams.
Ding Xiu-Huan; Zhang Cun-Xi; Wang Rui; Zhou Yun-Qing; Kong Ling-Min
2012-01-01
We have investigated theoretically the field-driven electron transport through a single-quantum-well semiconductor heterostructure with spin-orbit coupling.The splitting of the asymmetric Fano-type resonance peaks due to the Dresselhaus spin-orbit coupling is found to be highly sensitive to the direction of the incident electron.The splitting of the Fano-type resonance induces the spin-polarization dependent electron current.The location and the line shape of the Fano-type resonance can be controlled by adjusting the energy and the direction of the incident electron,the oscillation frequency,and the amplitude of the external field.These interesting features may be used to devise tunable spin filters and realize pure spin transmission currents.
Spin-electron acoustic waves: The Landau damping and ion contribution in the spectrum
Andreev, Pavel A
2014-01-01
Separated spin-up and spin-down quantum kinetics is derived for more detailed research of the spin-electron acoustic waves. Kinetic theory allows to obtain spectrum of the spin-electron acoustic waves including effects of occupation of quantum states more accurately than quantum hydrodynamics. We apply quantum kinetic to calculate the Landau damping of the spin-electron acoustic waves. We have considered contribution of ions dynamics in the spin-electron acoustic wave spectrum. We obtain contribution of ions in the Landau damping in temperature regime of classic ions. Kinetic analysis for ion-acoustic, zero sound, and Langmuir waves at separated spin-up and spin-down electron dynamics is presented as well.
Yu, Dong [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Jiang, Lan, E-mail: jianglan@bit.edu.cn [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Wang, Feng; Li, Xin [Laser Micro/Nano Fabrication Laboratory, School of Mechanical Engineering, Beijing Institute of Technology, Beijing 100081 (China); Qu, Liangti [Key Laboratory of Cluster Science, Ministry of Education, School of Chemistry, Beijing Institute of Technology, Beijing 100081 (China); Lu, Yongfeng [Department of Electrical Engineering, University of Nebraska-Lincoln, Lincoln, NE 68588-0511 (United States)
2015-10-23
We investigate the structural properties and ionized spin electrons of an Fe–graphene system, in which the time-dependent density functional theory (TDDFT) within the generalized gradient approximation is used. The electron dynamics, including electron ionization and ionized electron spin polarization, is described for Fe atom adsorbed graphene under femtosecond laser irradiation. The theoretical results show that the electron ionization and ionized electron spin polarization are sensitive to the laser parameters, such as the incident angle and the peak intensity. The spin polarization presents the maximum value under certain laser parameters, which may be used as a source of spin-polarized electrons. - Highlights: • The structural properties of Fe–graphene system are investigated. • The electron dynamics of Fe–graphene system under laser irradiation are described. • The Fe–graphene system may be used as a source of spin-polarized electrons.
Generation of a spin-polarized electron beam by multipole magnetic fields
Karimi, Ebrahim, E-mail: ekarimi@uottawa.ca [Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5 (Canada); Grillo, Vincenzo [CNR-Istituto Nanoscienze, Centro S3, Via G Campi 213/a, I-41125 Modena (Italy); Boyd, Robert W. [Department of Physics, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario, Canada K1N 6N5 (Canada); Institute of Optics, University of Rochester, Rochester, NY 14627 (United States); Santamato, Enrico [Dipartimento di Scienze Fisiche, Università di Napoli “Federico II”, Compl. Univ. di Monte S. Angelo, 80126 Napoli (Italy); Consorzio Nazionale Interuniversitario per le Scienze Fisiche della Materia, Napoli (Italy)
2014-03-01
The propagation of an electron beam in the presence of transverse magnetic fields possessing integer topological charges is presented. The spin–magnetic interaction introduces a nonuniform spin precession of the electrons that gains a space-variant geometrical phase in the transverse plane proportional to the field's topological charge, whose handedness depends on the input electron's spin state. A combination of our proposed device with an electron orbital angular momentum sorter can be utilized as a spin-filter of electron beams in a mid-energy range. We examine these two different configurations of a partial spin-filter generator numerically. The results of this analysis could prove useful in the design of an improved electron microscope. - Highlights: • Theory of generating spin-polarized electron beams. • Interacting electron vortex beams with space-variant magnetic fields. • Bohr–Pauli impossibility of generating spin-polarized free electrons.
Repeated quantum error correction by real-time feedback on continuously encoded qubits
Cramer, Julia; Kalb, Norbert; Rol, M. Adriaan; Hensen, Bas; Blok, Machiel S.; Markham, Matthew; Twitchen, Daniel J.; Hanson, Ronald; Taminiau, Tim H.
Because quantum information is extremely fragile, large-scale quantum information processing requires constant error correction. To be compatible with universal fault-tolerant computations, it is essential that quantum states remain encoded at all times and that errors are actively corrected. I will present such active quantum error correction in a hybrid quantum system based on the nitrogen vacancy (NV) center in diamond. We encode a logical qubit in three long-lived nuclear spins, detect errors by multiple non-destructive measurements using the optically active NV electron spin and correct them by real-time feedback. By combining these new capabilities with recent advances in spin control, multiple cycles of error correction can be performed within the dephasing time. We investigate both coherent and incoherent errors and show that the error-corrected logical qubit can indeed store quantum states longer than the best spin used in the encoding. Furthermore, I will present our latest results on increasing the number of qubits in the encoding, required for quantum error correction for both phase- and bit-flip.
Decoherence of an $n$-qubit quantum memory
Gorin, T; Seligman, T H; Gorin, Thomas; Pineda, Carlos; Seligman, Thomas H.
2007-01-01
We analyze decoherence of a quantum register in the absence of non-local operations i.e. of $n$ non-interacting qubits coupled to an environment. The problem is solved in terms of a sum rule which implies linear scaling in the number of qubits. Each term involves a single qubit and its entanglement with the remaining ones. Two conditions are essential: first decoherence must be small and second the coupling of different qubits must be uncorrelated in the interaction picture. We apply the result to a random matrix model, and illustrate its reach considering a GHZ state coupled to a spin bath.
Decoherence of an n-Qubit Quantum Memory
Gorin, Thomas; Pineda, Carlos; Seligman, Thomas H.
2007-12-01
We analyze decoherence of a quantum register in the absence of nonlocal operations, i.e., n noninteracting qubits coupled to an environment. The problem is solved in terms of a sum rule which implies linear scaling in the number of qubits. Each term involves a single qubit and its entanglement with the remaining ones. Two conditions are essential: first, decoherence must be small, and second, the coupling of different qubits must be uncorrelated in the interaction picture. We apply the result to a random matrix model, and illustrate its reach considering a Greenberger-Horne-Zeilinger state coupled to a spin bath.
Growth and Electronic Structure of Heusler Compounds for Use in Electron Spin Based Devices
Patel, Sahil Jaykumar
Spintronic devices, where information is carried by the quantum spin state of the electron instead of purely its charge, have gained considerable interest for their use in future computing technologies. For optimal performance, a pure spin current, where all electrons have aligned spins, must be generated and transmitted across many interfaces and through many types of materials. While conventional spin sources have historically been elemental ferromagnets, like Fe or Co, these materials pro duce only partially spin polarized currents. To increase the spin polarization of the current, materials like half-metallic ferromagnets, where there is a gap in the minority spin density of states around the Fermi level, or topological insulators, where the current transport is dominated by spin-locked surface states, show promise. A class of materials called Heusler compounds, with electronic structures that range from normal metals, to half metallic ferromagnets, semiconductors, superconductors and even topological insulators, interfaces well with existing device technologies, and through the use of molecular beam epitaxy (MBE) high quality heterostructures and films can be grown. This dissertation examines the electronic structure of surfaces and interfaces of both topological insulator (PtLuSb-- and PtLuBi--) and half-metallic ferromagnet (Co2MnSi-- and Co2FeSi--) III-V semiconductor heterostructures. PtLuSb and PtLuBi growth by MBE was demonstrated on Alx In1--xSb (001) ternaries. PtLuSb (001) surfaces were observed to reconstruct with either (1x3) or c(2x2) unit cells depending on Sb overpressure and substrate temperature. viii The electronic structure of these films was studied by scanning tunneling microscopy/spectroscopy (STM/STS) and photoemission spectroscopy. STS measurements as well as angle resolved photoemission spectropscopy (ARPES) suggest that PtLuSb has a zero-gap or semimetallic band structure. Additionally, the observation of linearly dispersing surface
Complete control of a matter qubit using a single picosecond laser pulse
Kodriano, Y; Poem, E; Benny, Y; Presman, R; Truong, T A; Petroff, P M; Gershoni, D
2012-01-01
We demonstrate for the first time that a matter physical two level system, a qubit, can be fully controlled using one ultrafast step. We show that the spin state of an optically excited electron, an exciton, confined in a quantum dot, can be rotated by any desired angle, about any desired axis, during such a step. For this we use a single, resonantly tuned, picosecond long, polarized optical pulse. The polarization of the pulse defines the rotation axis, while the pulse detuning from a non-degenerate absorption resonance, defines the magnitude of the rotation angle. We thereby achieve a high fidelity, universal gate operation, applicable to other spin systems, using only one short optical pulse. The operation duration equals the pulse temporal width, orders of magnitude shorter than the qubit evolution life and coherence times.
Origin of the spin-asymmetry of hot-electron transmission in Fe
Banerjee, T.; Lodder, J.C.; Jansen, R.
2007-01-01
Using the technique of ballistic electron magnetic microscopy, we have studied the spin-asymmetry of transmission of hot electrons in Fe, for which a recent ab initio calculation has shown that the inelastic lifetime is similar for majority and minority spin. Nevertheless, using a spin-valve structu
Spin-polarized transport in a two-dimensional electron gas with interdigital-ferromagnetic contacts
Hu, C.-M.; Nitta, Junsaku; Jensen, Ane
2001-01-01
Ferromagnetic contacts on a high-mobility, two-dimensional electron gas (2DEG) in a narrow gap semiconductor with strong spin-orbit interaction are used to investigate spin-polarized electron transport. We demonstrate the use of magnetized contacts to preferentially inject and detect specific spin...
Electron Spin Resonance Measurement with Microinductor on Chip
Akio Kitagawa
2011-01-01
Full Text Available The detection of radicals on a chip is demonstrated. The proposed method is based on electron spin resonance (ESR spectroscopy and the measurement of high-frequency impedance of the microinductor fabricated on the chip. The measurement was by using a frequency sweep of approximately 100 MHz. The ESR spectra of di(phenyl-(2,4,6-trinitrophenyliminoazanium (DPPH dropped on the microinductor which is fabricated with CMOS 350-nm technology were observed at room temperature. The volume of the DPPH ethanol solution was 2 μL, and the number of spins on the micro-inductor was estimated at about 1014. The sensitivity is not higher than that of the standard ESR spectrometers. However, the result indicates the feasibility of a near field radical sensor in which the microinductor as a probe head and ESR signal processing circuit are integrated.
Decoherence in Superconducting Qubits from Surface Magnetic States
Hover, David; Sendelbach, Steven; Kittel, Achim; Mueck, Michael; McDermott, Robert
2008-03-01
Unpaired spins in amorphous surface oxides can act as a source of decoherence in superconducting and other solid-state qubits. A density of surface spins can give rise to low-frequency magnetic flux noise, which in turn leads to dephasing of the qubit state. In addition, magnetic surface states can couple to high-frequency resonant magnetic fields, and thereby contribute to energy relaxation of the qubit. We present the results of low-frequency measurements of the nonlinear and imaginary spin susceptibility of surface magnetic states in superconducting devices at millikelvin temperatures. In addition, we describe high-frequency magnetic resonance measurements that directly probe the surface spin density of states. We present calculations that connect the measurement results to qubit energy relaxation and dephasing times.
Quantum Cryptography in Spin Networks
DENG Hong-Liang; FANG Xi-Ming
2007-01-01
In this paper we propose a new scheme of long-distance quantum cryptography based on spin networks with qubits stored in electron spins of quantum dots. By conditional Faraday rotation, single photon polarization measurement, and quantum state transfer, maximal-entangled Bell states for quantum cryptography between two long-distance parties are created. Meanwhile, efficient quantum state transfer over arbitrary distances is obtained in a spin chain by a proper choice of coupling strengths and using spin memory technique improved. We also analyse the security of the scheme against the cloning-based attack which can be also implemented in spin network and discover that this spin network cloning coincides with the optimal fidelity achieved by an eavesdropper for entanglement-based cryptography.
Electron spin from Goudsmit and Uhlenbeck to Spintronics
Levy, Peter M.
2010-03-01
While the electron's spin was postulated by Goudsmit and Uhlenbeck to explain atomic spectra of gases, it was adopted in a very different setting a decade later to explain the unusual physical and electrical transport properties of ferromagnetic metals. A discovery in 1988 lead to control currents through the spin of the electron, i.e., spintronics. The initial idea of spin dependent transport dates back to Neville Mott's work in the mid- thirties in which he developed the s-d or two current model of conduction in the 3d transition-metal ferromagnetic metals. The methodology used for semiconductor heterostructures lead one to grow high quality metallic multilayers by the 1980's, and it was apparent to Albert Fert and Peter Gr"unberg [Nobel Laureates in Physics 2007] that one could alter the magnetic configuration in ferromagnetic metals with moderate magnetic fields, and thereby change their resistivities. I will review the principle ideas and developments that lead to this new field, called Spintronics, and focus on developments in three distinct time periods. The first from 1988-1995 which was dominated by metallic multilayers which displayed giant magnetoresistance (GMR), the second from 1995-2000 when reproducible magnetic tunnel junctions (MTJ's) were studied for their tunneling magnetoresistance (TMR), and the third period from 2000-2005 in which the ideas of Berger and Slonczewski were realized on the back action of currents on the magnetic background of the materials doing the conducting, i.e., current induced magnetization switching (CIMS). Current interest has focused on spin dependent transport in oxides and carbon based materials. These developments illustrate the broad range of activities in Spintronics; a field which is barely twenty years old.
Spin qubits in antidot lattices
Pedersen, Jesper Goor; Flindt, Christian; Mortensen, Niels Asger;
2008-01-01
and density of states for a periodic potential modulation, referred to as an antidot lattice, and find that localized states appear, when designed defects are introduced in the lattice. Such defect states may form the building blocks for quantum computing in a large antidot lattice, allowing for coherent...
Spin Dynamics in Graphene and Graphene like Nanocarbon Doped with Nitrogen the ESR Analysis
Alegaonkar, Ashwini P; Pardeshi, Satish K; Alegaonkar, Prashant S
2013-01-01
Nano engineered spin degree of freedom in carbon system may offer desired exchange coupling with optimum spin orbit interaction which is essential, to construct solid state qubits, for fault tolerant quantum computation. The purpose of this communication is to analyze spin dynamics of, basically, four types of systems, (i) Graphene (system with inversion symmetry), (ii) Graphene like nanocarbons (GNCs, broken inversion symmetry and heterostructure, sp2 and sp3, environment), and (iii) their nitrogen doped derivatives. The spin transport data was obtained using the electron spin resonance spectroscopy (ESR) technique, carried out over 123 to 473K temperature range. Analysis of shape, linewidths of dispersion derivatives,, and g factor anisotropy has been carried out. Spin parameters such as, spin spin relaxation time, spin lattice relaxation time, spin flip parameter,spin relaxation rate,spin, momentum relaxation rate,pseudo chemical potential, density of states, effective magnetic moment, spin concentration, ...
An extended model for electron spin polarization in photosynthetic bacteria
Morris, A.L.; Norris, J.R. (Argonne National Lab., IL (USA) Chicago Univ., IL (USA). Dept. of Chemistry); Thurnauer, M.C. (Argonne National Lab., IL (USA))
1990-01-01
We have developed a general model for electron spin polarization which includes contributions from both CIDEP (chemically induced dynamic electron polarization) and CRP (correlated radical polarization). In this paper, we apply this model to sequential electron transfer in photosynthetic bacteria. Our model calculates the density matrix for the P{sup +}I{sup {minus}} radical pair and transfers the polarization as it develops to the P{sup +}Q{sup {minus}} radical pair. We illustrate several possible cases. One case is equivalent to CIDEP; no interactions are included on the secondary radical pair, P{sup +}Q{sup {minus}}. Another approximates CRPP by either increasing the transfer rate from P{sup +}I{sup {minus}} to P{sup +}Q{sup {minus}} or restricting interactions to the secondary radical pair, P{sup +}Q{sup {minus}}. Others allow interactions on both the primary and secondary radical pairs with various transfer rates. 15 refs., 4 figs.
Electron spin resonance and transient photocurrent measurements on microcrystalline silicon
Dylla, T.
2004-09-01
The electronic properties of microcrystalline silicon ({mu}c-Si:H) films have been studied using electron spin resonance (ESR), transient photocurrent time-of-flight (TOF) techniques, and electrical conductivity measurements. Structural properties were determined by Raman spectroscopy. A wide range of structure compositions, from highly crystalline films with no discernable amorphous content, to predominantly amorphous films with no crystalline phase contributions, was investigated. Models and possible explanations concerning the nature and energetic distribution of electronic defects as a function of film composition are discussed. It is shown that the spin density N{sub S} in {mu}c-Si:H films is linked strongly to the structure composition of the material. Both reversible and irreversible changes in the ESR signal and dark conductivity due to atmospheric effects are found in {mu}c-Si:H. The porous structure of highly crystalline material facilitates in-diffusion of atmospheric gases, which strongly affects the character and/or density of surface states. Two contributing processes have been identified, namely adsorption and oxidation. Both processes lead to an increase of N{sub S}. Measurements on n-type {mu}c-Si:H films were used as a probe of the density of gap states, confirming that the spin density NS is related to the density of defects. The results confirm that for a wide range of structural compositions, the doping induced Fermi level shift in {mu}c-Si:H is governed by compensation of defect states, for doping concentrations up to the dangling bond spin density. At higher concentrations a doping efficiency close to unity was found, confirming that in {mu}c-Si:H the measured spin densities represent the majority of gap states (N{sub S}=N{sub DB}). By applying the TOF technique to study pin solar cells based on {mu}c-Si:H, conclusive hole drift mobility data were obtained. Despite the predominant crystallinity of these samples, the temperature-dependence of
Lateral shifts of spin electron beams in antiparallel double {delta}-magnetic-barrier nanostructure
Kong Yonghong [Department of Electronic Engineering, Hunan University Science and Engineering, Hunan 425100 (China); Lu Maowang, E-mail: m_w_lu@126.com [Department of Electronic Engineering, Hunan University Science and Engineering, Hunan 425100 (China); Chen Saiyan; Zhang Guilian [Department of Electronic Engineering, Hunan University Science and Engineering, Hunan 425100 (China)
2012-08-15
We investigate the Goos-Haenchen (GH) effect of spin electron beams in a magnetic-barrier (MB) nanostructure consisting of antiparallel double {delta}-MBs, which can be experimentally realized by depositing two ferromagnetic (FM) stripes on top and bottom of the semiconductor heterostructure. GH shifts for spin electron beams across this type of MB nanostructures, is derived exactly, with the help of the stationary phase method. It is shown that GH shifts depend strongly on the spin directions for double {delta}-MBs with unidentical magnetic strengths, giving rise to a considerable spin polarization effect. It also is shown that spin polarization of GH shifts is closely relative to the separation and magnetic-strength difference of two {delta}-MBs. These interesting properties may provide an alternative scheme to spin-polarize electrons into the semiconductor, and the devices can serve as tunable spin beam splitters. - Highlights: Black-Right-Pointing-Pointer Spin Goos-Haenchen effect of electron beams through a kind of MB nanostructures. Black-Right-Pointing-Pointer GH shift depends greatly on electron-spins, which is used to spin polarize electrons in semiconductor. Black-Right-Pointing-Pointer Spin polarization in GH shift is tunable. Black-Right-Pointing-Pointer A tunable spin beam splitter is achieved.
Single-shot read-out of an individual electron spin in a quantum dot.
Elzerman, J M; Hanson, R; Willems Van Beveren, L H; Witkamp, B; Vandersypen, L M K; Kouwenhoven, L P
2004-07-22
Spin is a fundamental property of all elementary particles. Classically it can be viewed as a tiny magnetic moment, but a measurement of an electron spin along the direction of an external magnetic field can have only two outcomes: parallel or anti-parallel to the field. This discreteness reflects the quantum mechanical nature of spin. Ensembles of many spins have found diverse applications ranging from magnetic resonance imaging to magneto-electronic devices, while individual spins are considered as carriers for quantum information. Read-out of single spin states has been achieved using optical techniques, and is within reach of magnetic resonance force microscopy. However, electrical read-out of single spins has so far remained elusive. Here we demonstrate electrical single-shot measurement of the state of an individual electron spin in a semiconductor quantum dot. We use spin-to-charge conversion of a single electron confined in the dot, and detect the single-electron charge using a quantum point contact; the spin measurement visibility is approximately 65%. Furthermore, we observe very long single-spin energy relaxation times (up to approximately 0.85 ms at a magnetic field of 8 T), which are encouraging for the use of electron spins as carriers of quantum information.
Effect of electron-electron interactions on Rashba-like and spin-split systems
Alexandradinata, A.; Hirsch, J. E.
2010-11-01
The role of electron-electron interactions is analyzed for Rashba-like and spin-split systems within a tight-binding single-band Hubbard model with on-site and all nearest-neighbor matrix elements of the Coulomb interaction. By Rashba-like systems we refer to the Dresselhaus and Rashba spin-orbit-coupled phases while spin-split systems have spin-up and spin-down Fermi surfaces shifted relative to each other. Both systems break parity but preserve time-reversal symmetry. They belong to a class of symmetry-breaking ground states that satisfy: (i) electron crystal momentum is a good quantum number, (ii) these states have no net magnetic moment, and (iii) their distribution of “polarized spin” in momentum space breaks the lattice symmetry. For all members of this class, the relevant Coulomb matrix elements are found to be nearest-neighbor exchange J , pair hopping J' , and nearest-neighbor repulsion V . These ground states lower their energy most effectively through J , hence we name them class J states. The competing effects of V-J' on the direct and exchange energies determine the relative stability of class J states. We show that the spin-split and Rashba-like phases are the most favored ground states within class J because they have the minimum anisotropy in polarized spin. We analyze these two states on a square lattice and find that the spin-split phase is always favored for near-empty bands; above a critical filling, we predict a transition from the paramagnetic to the Rashba-like phase at a critical J(Jc1) and a second transition from the Rashba-like to the spin-split state at Jc2>Jc1 . An energetic comparison with ferromagnetism highlights the importance of the role of V in the stability of class J states. We discuss the relevance of our results to (i) the α and β phases proposed by Wu and Zhang in the Fermi-liquid formalism and (ii) experimental observations of spin-orbit splitting in Au(111) surface states.
Spin Relaxation of Electrons in Single InAs Quantum Dots
MA Shan-Shan; DOU Xiu-Ming; CHANG Xiu-Ying; SUN Bao-Quan; XIONG Yong-Hua; NIU Zhi-Chuan; NI Hai-Qiao
2009-01-01
By using polarization-resolved photoluminescence spectra, we study the electron spin relaxation in single InAs quantum dots (QDs) with the configuration of positively charged excitons X~+ (one electron, two holes). The spin relaxation rate of the hot electrons increases with the increasing energy of exciting photons. For electrons localized in QDs the spin relaxation is induced by hyperfine interaction with the nuclei. A rapid decrease of polarization degree with increasing temperature suggests that the spin relaxation mechanisms are mainly changed from the hyperfine interaction with nuclei into an electron-hole exchange interaction.
Using Superconducting Qubit Circuits to Engineer Exotic Lattice Systems
Tsomokos, Dimitris; Ashhab, Sahel; Nori, Franco
2011-03-01
We propose an architecture based on superconducting qubits and resonators for the implementation of a variety of exotic lattice systems, such as spin and Hubbard models in higher or fractal dimensions and higher-genus topologies. Spin systems are realized naturally using qubits, while superconducting resonators can be used for the realization of Bose-Hubbard models. Fundamental requirements for these designs, such as controllable interactions between arbitrary qubit pairs, have recently been implemented in the laboratory, rendering our proposals feasible with current technology.
Dempsey, Kari J; Ciudad, David; Marrows, Christopher H
2011-08-13
Single electron electronics is now well developed, and allows the manipulation of electrons one-by-one as they tunnel on and off a nanoscale conducting island. In the past decade or so, there have been concerted efforts in several laboratories to construct single electron devices incorporating ferromagnetic components in order to introduce spin functionality. The use of ferromagnetic electrodes with a non-magnetic island can lead to spin accumulation on the island. On the other hand, making the dot also ferromagnetic introduces new physics such as tunnelling magnetoresistance enhancement in the cotunnelling regime and manifestations of the Kondo effect. Such nanoscale islands are also found to have long spin lifetimes. Conventional spintronics makes use of the average spin-polarization of a large ensemble of electrons: this new approach offers the prospect of accessing the quantum properties of the electron, and is a candidate approach to the construction of solid-state spin-based qubits.
Interaction induced staggered spin-orbit order in two-dimensional electron gas
Das, Tanmoy [Los Alamos National Laboratory
2012-06-05
Decoupling spin and charge transports in solids is among the many prerequisites for realizing spin electronics, spin caloritronics, and spin-Hall effect. Beyond the conventional method of generating and manipulating spin current via magnetic knob, recent advances have expanded the possibility to optical and electrical method which are controllable both internally and externally. Yet, due to the inevitable presence of charge excitations and electrical polarizibility in these methods, the separation between spin and charge degrees of freedom of electrons remains a challenge. Here we propose and formulate an interaction induced staggered spin-orbit order as a new emergent phase of matter. We show that when some form of inherent spin-splitting via Rashba-type spin-orbit coupling renders two helical Fermi surfaces to become significantly nested, a Fermi surface instability arises. To lift this degeneracy, a spontaneous symmetry breaking spin-orbit density wave develops, causing a surprisingly large quasiparticle gapping with chiral electronic states, with no active charge excitations. Since the staggered spin-orbit order is associated with a condensation energy, quantified by the gap value, destroying such spin-orbit interaction costs sufficiently large perturbation field or temperature or de-phasing time. BiAg2 surface state is shown to be a representative system for realizing such novel spin-orbit interaction with tunable and large strength, and the spin-splitting is decoupled from charge excitations.
Spin g -factor due to electronic interactions in graphene
Menezes, Natália; Alves, Van Sérgio; Marino, E. C.; Nascimento, Leonardo; Nascimento, Leandro O.; Morais Smith, C.
2017-06-01
The gyromagnetic factor is an important physical quantity relating the magnetic-dipole moment of a particle to its spin. The electron spin g -factor in vacuo is one of the best model-based theoretical predictions ever made, showing agreement with the measured value up to ten parts per trillion [J. Schwinger, Phys. Rev. 73, 416 (1948), 10.1103/PhysRev.73.416; R. S. Van Dyck, Jr. et al., Phys. Rev. Lett. 59, 26 (1987), 10.1103/PhysRevLett.59.26; D. Hanneke et al., Phys. Rev. Lett. 100, 120801 (2008), 10.1103/PhysRevLett.100.120801; T. Aoyama et al., Phys. Rev. Lett. 109, 111807 (2012), 10.1103/PhysRevLett.109.111807]. However, for electrons in a material the g -factor is modified with respect to its value in vacuo because of environment interactions. Here, we show how interaction effects lead to the spin g -factor correction in graphene by considering the full electromagnetic interaction in the framework of pseudo-QED [A. Kovner et al., Phys. Rev. B 42, 4748 (1990), 10.1103/PhysRevB.42.4748; N. Dorey et al., Nucl. Phys. B 386, 614 (1992), 10.1016/0550-3213(92)90632-L; S. Teber, Phys. Rev. D 86, 025005 (2012), 10.1103/PhysRevD.86.025005; S. Teber, Phys. Rev. D 89, 067702 (2014), 10.1103/PhysRevD.89.067702; E. C. Marino, Nucl. Phys. B 408, 551 (1993), 10.1016/0550-3213(93)90379-4]. We compare our theoretical prediction with experiments performed on graphene deposited on SiO2 and SiC, and we find a very good agreement between them.
Electron spin resonance in Eu-based iron pnictides
Krug von Nidda, H.-A.; Kraus, S.; Schaile, S.; Dengler, E.; Pascher, N.; Hemmida, M.; Eom, M. J.; Kim, J. S.; Jeevan, H. S.; Gegenwart, P.; Deisenhofer, J.; Loidl, A.
2012-09-01
The phase diagrams of EuFe2-xCoxAs2 (0≤x≤0.4) and EuFe2As2-yPy (0≤y≤0.43) are investigated by Eu2+ electron spin resonance (ESR) in single crystals. From the temperature dependence of the linewidth ΔH(T) of the exchange narrowed ESR line, the spin-density wave (SDW) (TTSDW) are clearly distinguished. At T>TSDW the isotropic linear increase of the linewidth is driven by the Korringa relaxation which measures the conduction-electron density of states at the Fermi level. For Trate from 8 Oe/K at x=y=0 down to 3 Oe/K at the onset of superconductivity. For x>0.2 and y>0.3 it remains nearly constant. Comparative ESR measurements on single crystals of the Eu diluted SDW compound Eu0.2Sr0.8Fe2As2 and superconducting (SC) Eu0.22Sr0.78Fe1.72Co0.28As2 corroborate the leading influence of the ligand field on the Eu2+ spin relaxation in the SDW regime as well as the Korringa relaxation in the normal metallic regime. A coherence peak is not detected in the latter compound below Tc=21 K, which is in agreement with the expected complex anisotropic SC gap structure. In contrast, indications for phase coexistence and BCS-type superconductivity are found in EuFe2As1.57P0.43.
Electron spin polarization in strong-field ionization of xenon atoms
Hartung, Alexander; Morales, Felipe; Kunitski, Maksim; Henrichs, Kevin; Laucke, Alina; Richter, Martin; Jahnke, Till; Kalinin, Anton; Schöffler, Markus; Schmidt, Lothar Ph. H.; Ivanov, Misha; Smirnova, Olga; Dörner, Reinhard
2016-08-01
As a fundamental property of the electron, the spin plays a decisive role in the electronic structure of matter, from solids to molecules and atoms, for example, by causing magnetism. Yet, despite its importance, the spin dynamics of the electrons released during the interaction of atoms with strong ultrashort laser pulses has remained experimentally unexplored. Here, we report the experimental detection of electron spin polarization by the strong-field ionization of xenon atoms and support our results with theoretical analysis. We found up to 30% spin polarization changing its sign with electron energy. This work opens the new dimension of spin to strong-field physics. It paves the way to the production of sub-femtosecond spin-polarized electron pulses with applications ranging from probing the magnetic properties of matter at ultrafast timescales to testing chiral molecular systems with sub-femtosecond temporal and sub-ångström spatial resolutions.
Doppler Velocimetry of Current Driven Spin Helices in a Two-Dimensional Electron Gas
Yang, Luyi [Univ. of California, Berkeley, CA (United States)
2013-05-17
Spins in semiconductors provide a pathway towards the development of spin-based electronics. The appeal of spin logic devices lies in the fact that the spin current is even under time reversal symmetry, yielding non-dissipative coupling to the electric field. To exploit the energy-saving potential of spin current it is essential to be able to control it. While recent demonstrations of electrical-gate control in spin-transistor configurations show great promise, operation at room temperature remains elusive. Further progress requires a deeper understanding of the propagation of spin polarization, particularly in the high mobility semiconductors used for devices. This dissertation presents the demonstration and application of a powerful new optical technique, Doppler spin velocimetry, for probing the motion of spin polarization at the level of 1 nm on a picosecond time scale. We discuss experiments in which this technique is used to measure the motion of spin helices in high mobility n-GaAs quantum wells as a function of temperature, in-plane electric field, and photoinduced spin polarization amplitude. We find that the spin helix velocity changes sign as a function of wave vector and is zero at the wave vector that yields the largest spin lifetime. This observation is quite striking, but can be explained by the random walk model that we have developed. We discover that coherent spin precession within a propagating spin density wave is lost at temperatures near 150 K. This finding is critical to understanding why room temperature operation of devices based on electrical gate control of spin current has so far remained elusive. We report that, at all temperatures, electron spin polarization co-propagates with the high-mobility electron sea, even when this requires an unusual form of separation of spin density from photoinjected electron density. Furthermore, although the spin packet co-propagates with the two-dimensional electron gas, spin diffusion is strongly
Spin-Hall effect in two-dimensional electron systems with Rashba spin-orbit coupling and disorder.
Sheng, L; Sheng, D N; Ting, C S
2005-01-14
Using the four-terminal Landauer-Bu ttiker formula and Green's function approach, we calculate numerically the spin-Hall conductance in a two-dimensional junction system with the Rashba spin-orbit (SO) coupling and disorder. We find that the spin-Hall conductance can be much greater or smaller than the universal value e/8pi, depending on the magnitude of the SO coupling, the electron Fermi energy, and the disorder strength. The spin-Hall conductance does not vanish with increasing sample size for a wide range of disorder strength. Our numerical calculation reveals that a nonzero SO coupling can induce electron delocalization for disorder strength smaller than a critical value, and the nonvanishing spin-Hall effect appears mainly in the metallic regime.
Rao, K. Rama Koteswara; Suter, Dieter
2016-08-01
The nitrogen-vacancy (NV) center in diamond has attractive properties for a number of quantum technologies that rely on the spin angular momentum of the electron and the nuclei adjacent to the center. The nucleus with the strongest interaction is the 13C nuclear spin of the first shell. Using this degree of freedom effectively hinges on precise data on the hyperfine interaction between the electronic and the nuclear spin. Here, we present detailed experimental data on this interaction, together with an analysis that yields all parameters of the hyperfine tensor, as well as its orientation with respect to the atomic structure of the center.
Ferraro, E.; De Michielis, M.; Fanciulli, M.; Prati, E.
2015-01-01
Double-dot exchange-only qubit represents a promising compromise between high speed and simple fabrication in solid-state implementations. A couple of interacting double-dot exchange-only qubits, each composed by three electrons distributed in a double quantum dot, is exploited to realize controlled-NOT (CNOT) operations. The effective Hamiltonian model of the composite system is expressed by only exchange interactions between pairs of spins. Consequently, the evolution operator has a simple form and represents the starting point for the research of sequences of operations that realize CNOT gates. Two different geometrical configurations of the pair are considered, and a numerical mixed simplex and genetic algorithm is used. We compare the nonphysical case in which all the interactions are controllable from the external and the realistic condition in which intra-dot interactions are fixed by the geometry of the system. In the latter case, we find the CNOT sequences for both the geometrical configurations and we considered a qubit system where electrons are electrostatically confined in two quantum dots in a silicon nanowire. The effects of the geometrical sizes of the nanowire and of the gates on the fundamental parameters controlling the qubit are studied by exploiting a spin-density-functional theory-based simulator. Consequently, CNOT gate performances are evaluated.
Lijewski, S; Goslar, J; Hoffmann, S K
2006-07-05
The electron spin-lattice relaxation of Cu(2+) has been studied by the electron spin echo technique in the temperature range 4.2-115 K in triglycine sulfate (TGS) family crystals. Assuming that the relaxation is due to Raman relaxation processes the Debye temperature Θ(D) was determined as 190 K for TGS, 168 K for triglycine selenate (TGSe) and 179 K for triglycine fluoroberyllate (TGFB). We also calculated the Θ(D) values from the sound velocities derived from available elastic constants. The elastic Debye temperatures were found as 348 K for TGS, 288 K for TGSe and 372 K for TGFB. The results shown good agreement with specific heat data for TGS. The elastic Θ(D) are considerably larger than those determined from the Raman spin-lattice relaxation. The possible reasons for this discrepancy are discussed. We propose to use a modified expression describing two-phonon Raman relaxation with a single variable only (Θ(D)) after elimination of the sound velocity. Moreover, we show that the relaxation data can be fitted using the elastic Debye temperature value as a constant with an additional relaxation process contributing at low temperatures. This mechanism can be related to a local mode of the Cu(2+) defect in the host lattice. Electron paramagnetic resonance g-factors and hyperfine splitting were analysed in terms of the molecular orbital theory and the d-orbital energies and covalency factors of the Cu(gly)(2) complexes were found. Using the structural data and calculated orbital energies the spin-phonon coupling matrix element of the second-order Raman process was calculated as 553 cm(-1) for TGS, 742 cm(-1) for TGSe and 569 cm(-1) for TGFB.
Electron spin resonance characterization of a multi-nitrogen complex in diamond
Iakoubovskii, K
2002-01-01
The W27 centre has been characterized by means of electron spin resonance in natural diamond. The centre exhibits spin S=1, a large spin-spin coupling constant D=99 mT, and a complex hyperfine interaction structure interpreted as originating from interaction of an S=1 electronic system with five nitrogen atoms: two of these sites are equivalent and are located near the S = 1 electrons; three others are nearly equivalent and more remote. The centre is suggested to include a divacancy, where one vacancy, bound to two nitrogen atoms and one carbon atom, has trapped an extra electron, while the second vacancy is bound to three substitutional nitrogen atoms.
Room-temperature electron spin amplifier based on Ga(In)NAs alloys.
Puttisong, Yuttapoom; Buyanova, Irina A; Ptak, Aaron J; Tu, Charles W; Geelhaar, Lutz; Riechert, Henning; Chen, Weimin M
2013-02-06
The first experimental demonstration of a spin amplifier at room temperature is presented. An efficient, defect-enabled spin amplifier based on a non-magnetic semiconductor, Ga(In)NAs, is proposed and demonstrated, with a large spin gain (up to 2700% at zero field) for conduction electrons and a high cut-off frequency of up to 1 GHz.
Schapers, T; Nitta, J; Heersche, HB; Takayanagi, H
2002-01-01
The spin dependent conductance of a ferromagnet/two-dimensional electron gas ferromagnet structure is theoretically examined in the ballistic transport regime. It is shown that the spin signal can be improved considerably by making use of the spin filtering effect of a barrier at the ferromagnet two
Doping-dependent magnetization plateaus of a coupled spin-electron chain: exact results
Strečka, Jozef; Čisárová, Jana
2016-10-01
A coupled spin-electron chain composed of localized Ising spins and mobile electrons is exactly solved in an external magnetic field within the transfer-matrix method. The ground-state phase diagram involves in total seven different ground states, which differ in the number of mobile electrons per unit cell and the respective spin arrangements. A rigorous analysis of the low-temperature magnetization process reveals doping-dependent magnetization plateaus, which may be tuned through the density of mobile electrons. It is demonstrated that the fractional value of the electron density is responsible for an enhanced magnetocaloric effect due to an annealed bond disorder of the mobile electrons.
Fajer, Piotr G [Institute of Molecular Biophysics, Department of Biological Science, National High Magnetic Field Laboratory, Florida State University, Tallahassee, FL 32310 (United States)
2005-05-11
The recent development of site specific spin labelling and advances in pulsed electron paramagnetic resonance(EPR) have established spin labelling as a viable structural biology technique. Specific protein sites or whole domains can be selectively targeted for spin labelling by cysteine mutagenesis. The secondary structure of the proteins is determined from the trends in EPR signals of labels attached to consecutive residues. Solvent accessibility or label mobility display periodicities along the labelled polypeptide chain that are characteristic of {beta}-strands (periodicity of 2 residues) or {alpha}-helices (3.6 residues). Low-resolution 3D structure of proteins is determined from the distance restraints. Two spin labels placed within 60-70 A of each other create a local dipolar field experienced by the other spin labels. The strength of this field is related to the interspin distance, {proportional_to} r{sup -3}. The dipolar field can be measured by the broadening of the EPR lines for the short distances (8-20 A) or for the longer distances (17-70 A) by the pulsed EPR methods, double electron-electron resonance(DEER) and double quantum coherence (DQC). A brief review of the methodology and its applications to the multisubunit muscle protein troponin is presented below.
Possible Roles of Neural Electron Spin Networks in Memory and Consciousness
Hu, H P
2004-01-01
Spin is the origin of quantum effects in both Bohm and Hestenes quantum formulism and a fundamental quantum process associated with the structure of space-time. Thus, we have recently theorized that spin is the mind-pixel and developed a qualitative model of consciousness based on nuclear spins inside neural membranes and proteins. In this paper, we explore the possibility of unpaired electron spins being the mind-pixels. Besides free O2 and NO, the main sources of unpaired electron spins in neural membranes and proteins are transition metal ions and O2 and NO bound/absorbed to large molecules, free radicals produced through biochemical reactions and excited molecular triplet states induced by fluctuating internal magnetic fields. We show that unpaired electron spin networks inside neural membranes and proteins are modulated by action potentials through exchange and dipolar coupling tensors and spin-orbital coupling and g-factor tensors and perturbed by microscopically strong and fluctuating internal magnetic...
XIONG Jian-Wen; HU Liang-Bin; ZHANG Zhen-Xi
2006-01-01
@@ Based on the Heisenberg equations of motion for the electron orbital and spin degrees of freedom in two-dimensional electronic systems with both Rashba and Dresselhaus spin-orbit couplings, we show that an ac electric field can cause an ac spin Hall current in such a system. In contrast to some previous theoretical prediction, the spin Hall current will be suppressed completely in the dc limit. We argue that the suppression of dc spin Hall currents in such a system is actually a much natural result of the dynamic spin evolution due to the combined action of a dc external electric field and the intrinsic spin-orbit coupling.
Electron spin relaxation of a boron-containing heterocyclic radical
Eaton, Sandra S.; Huber, Kirby; Elajaili, Hanan; McPeak, Joseph; Eaton, Gareth R.; Longobardi, Lauren E.; Stephan, Douglas W.
2017-03-01
Preparation of the stable boron-containing heterocyclic phenanthrenedione radical, (C6F5)2B(O2C14H8), by frustrated Lewis pair chemistry has been reported recently. Electron paramagnetic resonance measurements of this radical were made at X-band in toluene:dichloromethane (9:1) from 10 to 293 K, in toluene from 180 to 293 K and at Q-band at 80 K. In well-deoxygenated 0.1 mM toluene solution at room temperature hyperfine splittings from 11B, four pairs of 1H, and 5 pairs of 19F contribute to an EPR spectrum with many resolved lines. Observed hyperfine couplings were assigned based on DFT calculations and account for all of the fluorines and protons in the molecule. Rigid lattice g values are gx = 2.0053, gy = 2.0044, and gz = 2.0028. Near the melting point of the solvent 1/Tm is enhanced due to motional averaging of g and A anisotropy. Increasing motion above the melting point enhances 1/T1 due to contributions from tumbling-dependent processes. The overall temperature dependence of 1/T1 from 10 to 293 K was modeled with the sum of contributions of a process that is linear in T, a Raman process, spin rotation, and modulation of g anisotropy by molecular tumbling. The EPR measurements are consistent with the description of this compound as a substituted aromatic radical, with relatively small spin density on the boron.
Silicon-based spin and charge quantum computation
Belita Koiller
2005-06-01
Full Text Available Silicon-based quantum-computer architectures have attracted attention because of their promise for scalability and their potential for synergetically utilizing the available resources associated with the existing Si technology infrastructure. Electronic and nuclear spins of shallow donors (e.g. phosphorus in Si are ideal candidates for qubits in such proposals due to the relatively long spin coherence times. For these spin qubits, donor electron charge manipulation by external gates is a key ingredient for control and read-out of single-qubit operations, while shallow donor exchange gates are frequently invoked to perform two-qubit operations. More recently, charge qubits based on tunnel coupling in P+2 substitutional molecular ions in Si have also been proposed. We discuss the feasibility of the building blocks involved in shallow donor quantum computation in silicon, taking into account the peculiarities of silicon electronic structure, in particular the six degenerate states at the conduction band edge. We show that quantum interference among these states does not significantly affect operations involving a single donor, but leads to fast oscillations in electron exchange coupling and on tunnel-coupling strength when the donor pair relative position is changed on a lattice-parameter scale. These studies illustrate the considerable potential as well as the tremendous challenges posed by donor spin and charge as candidates for qubits in silicon.Arquiteturas de computadores quânticos baseadas em silício vêm atraindo atenção devido às suas perspectivas de escalabilidade e utilização dos recursos já instalados associados à tecnologia do Si. Spins eletrônicos e nucleares de doadores rasos (por exemplo fósforo em Si são candidatos ideais para bits quânticos (qubits nestas propostas, devido aos tempos de coerência relativamente longos dos spins em matrizes de Si. Para estes qubits de spin, a manipulação da carga do elétron do doador
Bartucci, R; Gambacorta, A; Gliozzi, A; Marsh, D; Sportelli, L
2005-11-15
Membranes of thermophilic Archaea are composed of unique tetraether lipids in which C40, saturated, methyl-branched biphytanyl chains are linked at both ends to polar groups. In this paper, membranes composed of bipolar lipids P2 extracted from the acidothermophile archaeon Sulfolobus solfataricus are studied. The biophysical basis for the membrane formation and thermal stability is investigated by using electron spin resonance (ESR) of spin-labeled lipids. Spectral anisotropy and isotropic hyperfine couplings are used to determine the chain flexibility and polarity gradients, respectively. For comparison, similar measurements have been carried out on aqueous dispersions of diacyl reference lipid dipalmitoyl phosphatidylcholine and also of diphytanoyl phosphatidylcholine, which has methyl-branched chains. At a given temperature, the bolaform lipid chains are more ordered and less flexible than in normal bilayer membranes. Only at elevated temperatures (80 degrees C) does the flexibility of the chain environment in tetraether lipid assemblies approach that of fluid bilayer membranes. The height of the hydrophobic barrier formed by a monolayer of archaebacterial lipids is similar to that in conventional fluid bilayer membranes, and the permeability barrier width is comparable to that formed by a bilayer of C16 lipid chains. At a mole ratio of 1:2, the tetraether P2 lipids mix well with dipalmitoyl phosphatidylcholine lipids and stabilize conventional bilayer membranes. The biological as well as the biotechnological relevance of the results is discussed.
Thermal History of Archaeological Objects, Studied by Electron Spin Resonance
Bartoll, Jens; Tani, Atsushi
Electron spin resonance (ESR) spectroscopy is a sensitive tool for distinguishing between "burned" and "unburned" states of archaeological objects. Prehistoric heating conditions, such as the temperature, atmosphere, time of exposure to heat, and when the heating took place, can be studied by this method with some success. ESR "reporters," such as (a) radiation defects, (b) pyrolytic defects, and (c) transition metal ions, can even reflect changes induced at relatively low temperatures (e.g., in the range of 200° C for objects containing organic compounds). Several ESR heating markers are so stable that samples dating back to the ages when fire first began to be used can be analyzed today. An overview is presented of the literature concerning objects, such as stone, soil, pottery, and plant and animal products.
Intrinsic and Extrinsic Spin Hall Effects of Dirac Electrons
Fukazawa, Takaaki; Kohno, Hiroshi; Fujimoto, Junji
2017-09-01
We investigate the spin Hall effect (SHE) of electrons described by the Dirac equation, which is used as an effective model near the L-points in bismuth. By considering short-range nonmagnetic impurities, we calculate the extrinsic as well as intrinsic contributions on an equal footing. The vertex corrections are taken into account within the ladder type and the so-called skew-scattering type. The intrinsic SHE which we obtain is consistent with that of Fuseya et al. [https://doi.org/10.1143/JPSJ.81.093704" xlink:type="simple">J. Phys. Soc. Jpn. 81, 093704 (2012)]. It is found that the extrinsic contribution dominates the intrinsic one when the system is metallic. The extrinsic SHE due to the skew scattering is proportional to Δ/niu, where 2Δ is the band gap, ni is the impurity concentration, and u is the strength of the impurity potential.
Nanoscale microwave imaging with a single electron spin in diamond
Appel, Patrick; Ganzhorn, Marc; Neu, Elke; Maletinsky, Patrick
2015-11-01
We report on imaging of microwave (MW) magnetic fields using a magnetometer based on the electron spin of a nitrogen vacancy (NV) center in diamond. We quantitatively image the magnetic field generated by high frequency (GHz) MW current with nanoscale resolution using a scanning probe technique. Together with a shot noise limited MW magnetic field sensitivity of 680 nT Hz-1/2 our room temperature experiments establish the NV center as a versatile and high performance tool for MW imaging, which furthermore offers polarization selectivity and broadband capabilities. As a first application of this scanning MW detector, we image the MW stray field around a stripline structure and thereby locally determine the MW current density with a MW current sensitivity of a few nA Hz-1/2.
Electron Transfer Reactions: Generalized Spin-Boson Approach
Merkli, Marco
2012-01-01
We introduce a mathematically rigorous analysis of a generalized spin-boson system for the treatment of a donor-acceptor (reactant-product) quantum system coupled to a thermal quantum noise. The donor/acceptor probability dynamics describes transport reactions in chemical processes in presence of a noisy environment -- such as the electron transfer in a photosynthetic reaction center. Besides being rigorous, our analysis has the advantages over previous ones that (1) we include a general, non energy-conserving system-environment interaction, and that (2) we allow for the donor or acceptor to consist of multiple energy levels lying closely together. We establish explicit expressions for the rates and the efficiency (final donor-acceptor population difference) of the reaction. In particular, we show that the rate increases for a multi-level acceptor, but the efficiency does not.
Electron spin resonance from semiconductor-metal separated SWCNTs
Havlicek, M.; Jantsch, W. [Institut fuer Halbleiter- und Festkoerperphysik, Johannes Kepler Universitaet, 4040 Linz (Austria); Ruemmeli, M.; Schoenfelder, R. [Leibniz Institute fuer Festkoerperphysik und Werkstoffforschung, Dresden (Germany); Yanagi, K. [Department of Physics, Tokyo Metropolitan University, Hachioji, Tokyo (Japan); Miyata, Y. [Department of Chemistry, Nagoya University, Nagoya, Aichi (Japan); Kataura, H. [Nanotechnology Research Institute, AIST, 1-1-1 Higashi, Tsukuba 305-8562 (Japan); Simon, F.; Peterlik, H.; Kuzmany, H. [Fakultaet fuer Physik, Universitaet Wien, Strudlhofgasse 4, 1090 Wien (Austria)
2010-12-15
Electron spin resonance in the X band is reported for fully metal-semiconductor separated SWCNTs. For the experiments samples were immersed in ethanol or wrapped into a teflon foil. The response from the metallic tubes exhibits a strong asymmetry in the line shape whereas the asymmetry for the semiconducting (SC) tubes is comparatively small. In both cases the line widths are unusual small, of the order of 4 G. Particular attention is paid to SC nanotubes which exhibit a much stronger signal as compared to the metallic tubes. The signal intensity is nearly Curie like with a small enhancement beyond 1/T in the low temperature range. The 1/T behavior renders the ESR response unobservable at 300 K. The finite value for the asymmetry parameter in the SC tubes is assumed to originate from charges picked up during exposure to air or to ethanol. (Copyright copyright 2010 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Effect of electronic reconstruction on cuprate-manganite spin switches.
Liu, Y.; Visani, C.; Nemes, N. M.; Fitzsimmons, M. R.; Zhu, L. Y.; Tornos, J.; Zhernenkov, M.; Hoffmann, A.; Leon, C.; Santamaria, J.; te Velthuis, S. G. E. (Materials Science Division); (Universidad Complutense de Madrid); (LANL)
2012-01-01
We examine the anomalous inverse spin switch behavior in La{sub 0.7}Ca{sub 0.3}MnO{sub 3}(LCMO)/YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO)/LCMO trilayers by combined transport studies and polarized neutron reflectometry. Measuring magnetization profiles and magnetoresistance in an in-plane rotating magnetic field, we prove that, contrary to many accepted theoretical scenarios, the relative orientation between the two LCMO's magnetizations is not sufficient to determine the magnetoresistance. Rather the field dependence of magnetoresistance is explained by the interplay between the applied magnetic field and the (exponential tail of the) induced exchange field in YBCO, the latter originating from the electronic reconstruction at the LCMO/YBCO interfaces.
Generation of a spin-polarized electron beam by multipoles magnetic fields
Karimi, Ebrahim; Boyd, Robert W; Santamato, Enrico
2013-01-01
The propagation of an electron beam in the presence of transverse magnetic fields possessing integer topological charges is presented. The spin--magnetic interaction introduces a nonuniform spin precession of the electrons that gains a space-variant geometrical phase in the transverse plane proportional to the field's topological charge, whose handedness depends on the input electron's spin state. A combination of our proposed device with an electron orbital angular momentum sorter can be utilized as a spin-filter of electron beams in a mid-energy range. We examine these two different configurations of a partial spin-filter generator numerically. The results of these analysis could prove useful in the design of improved electron microscope.
van Gastel, Maurice
2009-09-28
Spin polarization effects play an important role in the theory of isotropic hyperfine interactions for aromatic protons. The spin polarization gives rise to significant isotropic proton hyperfine interactions--spin-dependent one-electron properties--smaller than 0 MHz and the effect has been theoretically described [H. M. McConnell and D. B. J. Chesnut, Chem. Phys. 28, 107 (1958)]. The influence of spin polarization on the zero field splitting parameters, which are spin-dependent two-electron properties, has not been clearly identified yet. A phenomenological equation is proposed here for the contribution of spin polarization to the zero field splitting parameter D in analogy to McConnell's equation for hyperfine interactions. The presence of the effect is demonstrated in a series of calculations on polyacenes in the triplet state and turns out to be responsible for up to 50% of the D parameter in the case of naphthalene! It is found that spin-unrestricted single-determinant methods, including the widely used density functional theory methods, do not accurately reproduce the two-electron reduced electron density required for the evaluation of two-electron spin-dependent properties. For the accurate calculation of zero field splitting parameters by quantum chemical methods, it thus seems necessary to resort to correlated ab initio methods which do not give rise to spin contamination and which do provide an accurate description of the two-electron reduced electron density.
Higemoto, Wataru; Aoki, Yuji; MacLaughlin, Douglas E.
2016-09-01
Unconventional superconductivity based on the strong correlation of electrons is one of the central issues of solid-state physics. Although many experimental techniques are appropriate for investigating unconventional superconductivity, a complete perspective has not been established yet. The symmetries of electron pairs are crucial properties for understanding the essential state of unconventional superconductivity. In this review, we discuss the investigation of the time-reversal and spin symmetries of superconducting electron pairs using the muon spin rotation and relaxation technique. By detecting a spontaneous magnetic field under zero field and/or the temperature dependence of the muon Knight shift in the superconducting phase, the time-reversal symmetry and spin parity of electron pairs have been determined for several unconventional superconductors.
Entanglement between qubits induced by a common environment with a gap
Oh, S; Oh, Sangchul; Kim, Jaewan
2006-01-01
We study a system of two qubits interacting with a common environment, described by a two-spin boson model. We demonstrate two competing roles of the environment: inducing entanglement between the two qubits and making them decoherent. For the environment of a single harmonic oscillator, if its frequency is commensurate with the induced two-qubit coupling strength, the two qubits could be maximally entangled and the environment could be separable. In the case of the environment of a bosonic bath, the gap of its spectral density function is essential to generate entanglement between two qubits at equilibrium and for it to be used as a quantum data bus.
Electrically detected electron spin resonance in a high-mobility silicon quantum well.
Matsunami, Junya; Ooya, Mitsuaki; Okamoto, Tohru
2006-08-11
The resistivity change due to electron spin resonance (ESR) absorption is investigated in a high-mobility two-dimensional electron system formed in a Si/SiGe heterostructure. Results for a specific Landau level configuration demonstrate that the primary cause of the ESR signal is a reduction of the spin polarization, not the effect of electron heating. The longitudinal spin relaxation time T1 is obtained to be of the order of 1 ms in an in-plane magnetic field of 3.55 T. The suppression of the effect of the Rashba fields due to high-frequency spin precession explains the very long T1.
Photon-assisted spin transport in a two-dimensional electron gas
Fistul, M. V.; Efetov, K. B.
2007-01-01
We study spin-dependent transport in a two-dimensional electron gas subject to an external step-like potential $V(x)$ and irradiated by an electromagnetic field (EF). In the absence of EF the electronic spectrum splits into spin sub-bands originating from the "Rashba" spin-orbit coupling. We show that the resonant interaction of propagating electrons with the component EF parallel to the barrier induces a \\textit{% non-equilibrium dynamic gap} $(2\\Delta_{R})$ between the spin sub-bands. Exist...
Andreev, Pavel A
2016-01-01
Hydrodynamics analysis of waves in two-dimensional degenerate electron gas with the account of separate spin evolution is presented. The transverse electric field is included along with the longitudinal electric field. The Coulomb exchange interaction is included in the analysis. In contrast with the three-dimensional plasma-like mediums the contribution of the transverse electric field is small. We show the decrease of frequency of both the extraordinary (Langmuir) wave and the spin-electron acoustic wave due to the exchange interaction. Moreover, spin-electron acoustic wave has negative dispersion at the relatively large spin-polarization. Corresponding dispersion dependencies are presented and analyzed.
Engineering the quantum-classical interface of solid-state qubits
Reilly, David J.
2015-10-01
Spanning a range of hardware platforms, the building-blocks of quantum processors are today sufficiently advanced to begin work on scaling-up these systems into complex quantum machines. A key subsystem of all quantum machinery is the interface between the isolated qubits that encode quantum information and the classical control and readout technology needed to operate them. As few-qubit devices are combined to construct larger, fault-tolerant quantum systems in the near future, the quantum-classical interface will pose new challenges that increasingly require approaches from the engineering disciplines in combination with continued fundamental advances in physics, materials and mathematics. This review describes the subsystems comprising the quantum-classical interface from the viewpoint of an engineer, experimental physicist or student wanting to enter the field of solid-state quantum information technology. The fundamental signalling operations of readout and control are reviewed for a variety of qubit platforms, including spin systems, superconducting implementations and future devices based on topological degrees-of-freedom. New engineering opportunities for technology development at the boundary between qubits and their control hardware are identified, transversing electronics to cryogenics.
Yu, Hua-Liang; Zhang, Xiu-Min; Wang, Peng-Fei; Ni, Hai-Qiao; Niu, Zhi-Chuan; Lai, Tianshu
2009-05-01
Circular dichromatic absorption difference spectroscopy is developed to measure the spin diffusion dynamics of electrons in bulk n-GaAs. This spectroscopy has higher detection sensitivity over homodyne detection of spin-grating-diffracted signal. A model to describe circular dichromatic absorption difference signal is derived and used to fit experimental signal to retrieve decaying rate of spin gratings. A spin diffusion constant of Ds=201±25 cm2/s for bulk n-GaAs has been measured at room temperature using this technique and is close to electron diffusion constant (Dc), which is much different from the case in GaAs quantum wells where Ds is markedly less than Dc.
Van der Sluijs, A.M.; Drouhin, H.J.; Lampel, G.; Lassailly, Y.; Marliere, C. [Ecole Polytechnique, 91 - Palaiseau (France)
1994-10-01
At low energy, a longitudinally spin-polarized electron beam impinges on an ultrathin, self-supported ferromagnetic target, consisting of a 1 nm-thick cobalt film sandwiched between 21 and 2 nm-thick gold layers, and which is magnetized perpendicularly to the surface. The current transmitted by the target depends on the spin of the electrons. Cesium deposition on both sides of the target increases the transmission ratio from about 1 x 10{sup -5} up to 3 x 10{sup -4} and also increases the transmission spin-asymmetry from 15 to about 40%. Such a structure is well suited to the construction of convenient and compact spin-detectors. (authors). 4 figs., 9 refs.
Spin-Dependent Goos-Hanchen Effect in Semiconducting Quantum Dots
Abdelrazek, Ahmed S.; Zein, Walid A.; Phillips, Adel H.
2013-08-01
The present research is devoted to the investigation of the spin-dependant Goos-Hanchen phase shift in quantum nanodevice. This nanodevice is modeled as semiconducting quantum dot coupled to two ferromagnetic leads. The spin transport through such nanodevice is conducted under the effect of both magnetic field and the photon energy of the induced ac-field. The angle of incidence of electrons is taken into account. Results show that the Goos-Hanchen phase shift of spin-up electrons is different from that of spin-down electron. Also, spin polarization and giant magneto-resistance are strongly depending on the angle of incidence of electrons and the photon energy of the induced ac-field. The present model could realize experimentally the spin beam splitter and spin filter needed for spin qubits and quantum information processing.
Majd, Nayereh; Ghasemi, Zahra
2016-10-01
We have investigated a TPTQ state as an input state of a non-ideal ferromagnetic detectors. Minimal spin polarization required to demonstrate spin entanglement according to entanglement witness and CHSH inequality with respect to (w.r.t.) their two free parameters have been found, and we have numerically shown that the entanglement witness is less stringent than the direct tests of Bell's inequality in the form of CHSH in the entangled limits of its free parameters. In addition, the lower limits of spin detection efficiency fulfilling secure cryptographic key against eavesdropping have been derived. Finally, we have considered TPTQ state as an output of spin decoherence channel and the region of ballistic transmission time w.r.t. spin relaxation time and spin dephasing time has been found.
Spatially confined electron spin diffusion in quasi-one-dimensional organic conductors
Wokrina, T
2002-01-01
After an introduction to the substances and some important properties of them the measurement principle, the time-resolved electron spin resonance is presented. Then the foundations and the technical realization of an image-shaping procedure on the base of electron spin tomography are described. The measurement of the spin dynamics for the three radical-ion salts form the main part and the conclusion of this thesis.
Electron spin dynamics in GaAsN and InGaAsN structures
Lagarde, D.; Lombez, L.; Marie, X.; Balocchi, A.; Amand, T. [Laboratoire de Nanophysique, Magnetisme et Optoelectronique, INSA 135 avenue de Rangueil 31077 Toulouse Cedex 4 (France); Kalevich, V.K.; Shiryaev, A.; Ivchenko, E.; Egorov, A. [A.F. Ioffe Physico-Technical Institute, 194021 St-Petersburg (Russian Federation)
2007-01-15
We report on optical orientation experiments in undoped GaAsN epilayers and InGaAsN quantum wells (QW), showing that a strong electron spin polarisation can persist at room temperature. We demonstrate that the spin dynamics in these dilute nitride structures is governed by a spin-dependent recombination process of free conduction electrons on deep paramagnetic centres. (copyright 2007 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Pauli Spin Paramagnetism and Electronic Specific Heat in Generalised d-Dimensions
Muktish Acharyya
2011-01-01
The variations of pauli spin paramagnetic susceptibility and the electronic specific heat of solids, are calculated as functions of temperature following the free electron approximation, in generalised d-dimensions.The results are compared and become consistent with that obtained in three dimensions.Interestingly, the Pauli spin paramagnetic susceptibility becomes independent of temperature only in two dimensions.
Relaxation of the electron spin in quantum dots via one- and two-phonon processes
Calero, C. [Department of Physics and Astronomy, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, NY 10468-1589 (United States)]. E-mail: carlos.calero-borrallo@lehman.cuny.edu; Chudnovsky, E.M. [Department of Physics and Astronomy, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, NY 10468-1589 (United States); Garanin, D.A. [Department of Physics and Astronomy, Lehman College, City University of New York, 250 Bedford Park Boulevard West, Bronx, NY 10468-1589 (United States)
2007-09-15
We have studied direct and Raman processes of the decay of electron spin states in a quantum dot via radiation of phonons corresponding to elastic twists. Universal dependence of the spin relaxation rate on the strength and direction of the magnetic field has been obtained in terms of the electron gyromagnetic tensor and macroscopic elastic constants of the solid.
Guo, G P; Hao, X J; Tu, T; Zhu, Z C; Guo, Guang-Can; Guo, Guo-Ping; Hao, Xiao-Jie; Tu, Tao; Zhu, Zhi-Cheng
2007-01-01
We propose a scheme to eliminate the effect of non-nearest-neighbor qubits in preparing cluster state with double-dot molecules. As the interaction Hamiltonians between qubits are Ising-model and mutually commute, we can get positive and negative effective interactions between qubits to cancel the effect of non-nearest-neighbor qubits by properly changing the electron charge states of each quantum dot molecule. The total time for the present multi-step cluster state preparation scheme is only doubled for one-dimensional qubit chain and tripled for two-dimensional qubit array comparing with the time of previous protocol leaving out the non-nearest-neighbor interactions.
1H relaxation dispersion in solutions of nitroxide radicals: Influence of electron spin relaxation
Kruk, D.; Korpała, A.; Kubica, A.; Kowalewski, J.; Rössler, E. A.; Moscicki, J.
2013-03-01
The work presents a theory of nuclear (1H) spin-lattice relaxation dispersion for solutions of 15N and 14N radicals, including electron spin relaxation effects. The theory is a generalization of the approach presented by Kruk et al. [J. Chem. Phys. 137, 044512 (2012)], 10.1063/1.4736854. The electron spin relaxation is attributed to the anisotropic part of the electron spin-nitrogen spin hyperfine interaction modulated by rotational dynamics of the paramagnetic molecule, and described by means of Redfield relaxation theory. The 1H relaxation is caused by electron spin-proton spin dipole-dipole interactions which are modulated by relative translational motion of the solvent and solute molecules. The spectral density characterizing the translational dynamics is described by the force-free-hard-sphere model. The electronic relaxation influences the 1H relaxation by contributing to the fluctuations of the inter-molecular dipolar interactions. The developed theory is tested against 1H spin-lattice relaxation dispersion data for glycerol solutions of 4-oxo-TEMPO-d16-15N and 4-oxo-TEMPO-d16-14N covering the frequency range of 10 kHz-20 MHz. The studies are carried out as a function of temperature starting at 328 K and going down to 290 K. The theory gives a consistent overall interpretation of the experimental data for both 14N and 15N systems and explains the features of 1H relaxation dispersion resulting from the electron spin relaxation.
Observation of Spin Coulomb Drag in a Two-Dimensional Electron Gas
Weber, C.P.
2011-08-19
An electron propagating through a solid carries spin angular momentum in addition to its mass and charge. Of late there has been considerable interest in developing electronic devices based on the transport of spin, which offer potential advantages in dissipation, size, and speed over charge-based devices. However, these advantages bring with them additional complexity. Because each electron carries a single, fixed value (-e) of charge, the electrical current carried by a gas of electrons is simply proportional to its total momentum. A fundamental consequence is that the charge current is not affected by interactions that conserve total momentum, notably collisions among the electrons themselves. In contrast, the electron's spin along a given spatial direction can take on two values, {+-} {h_bar}/2 (conventionally {up_arrow}, {down_arrow}), so that the spin current and momentum need not be proportional. Although the transport of spin polarization is not protected by momentum conservation, it has been widely assumed that, like the charge current, spin current is unaffected by electron-electron (e-e) interactions. Here we demonstrate experimentally not only that this assumption is invalid, but that over a broad range of temperature and electron density, the flow of spin polarization in a two-dimensional gas of electrons is controlled by the rate of e-e collisions.
Demonstration of entanglement of electrostatically coupled singlet-triplet qubits.
Shulman, M D; Dial, O E; Harvey, S P; Bluhm, H; Umansky, V; Yacoby, A
2012-04-13
Quantum computers have the potential to solve certain problems faster than classical computers. To exploit their power, it is necessary to perform interqubit operations and generate entangled states. Spin qubits are a promising candidate for implementing a quantum processor because of their potential for scalability and miniaturization. However, their weak interactions with the environment, which lead to their long coherence times, make interqubit operations challenging. We performed a controlled two-qubit operation between singlet-triplet qubits using a dynamically decoupled sequence that maintains the two-qubit coupling while decoupling each qubit from its fluctuating environment. Using state tomography, we measured the full density matrix of the system and determined the concurrence and the fidelity of the generated state, providing proof of entanglement.
Doppler Velocimetry of Current Driven Spin Helices in a Two-Dimensional Electron Gas
Yang, Luyi
Spins in semiconductors provide a pathway towards the development of spin-based electronics. The appeal of spin logic devices lies in the fact that the spin current is even under time reversal symmetry, yielding non-dissipative coupling to the electric field. To exploit the energy-saving potential of spin current it is essential to be able to control it. While recent demonstrations of electrical-gate control in spin-transistor configurations show great promise, operation at room temperature remains elusive. Further progress requires a deeper understanding of the propagation of spin polarization, particularly in the high mobility semiconductors used for devices. This thesis presents the demonstration and application of a powerful new optical technique, Doppler spin velocimetry, for probing the motion of spin polarization at the level of 1 nm on a picosecond time scale. We discuss experiments in which this technique is used to measure the motion of spin helices in high mobility n-GaAs quantum wells as a function of temperature, in-plane electric field, and photoinduced spin polarization amplitude. We find that the spin helix velocity changes sign as a function of wave vector and is zero at the wave vector that yields the largest spin lifetime. This observation is quite striking, but can be explained by the random walk model that we have developed. We discover that coherent spin precession within a propagating spin density wave is lost at temperatures near 150 K. This finding is critical to understanding why room temperature operation of devices based on electrical gate control of spin current has so far remained elusive. We report that, at all temperatures, electron spin polarization co-propagates with the high-mobility electron sea, even when this requires an unusual form of separation of spin density from photoinjected electron density. Furthermore, although the spin packet co-propagates with the two-dimensional electron gas, spin diffusion is strongly suppressed
Electronic spin transport in graphene field-effect transistors
Popinciuc, M.; Jozsa, C.; Zomer, P. J.; Tombros, N.; Veligura, A.; Jonkman, H. T.; van Wees, B. J.
2009-01-01
Spin transport experiments in graphene, a single layer of carbon atoms ordered in a honeycomb lattice, indicate spin-relaxation times that are significantly shorter than the theoretical predictions. We investigate experimentally whether these short spin-relaxation times are due to extrinsic factors,
Environmental effects on electron spin relaxation in N@C60
Morton, J J L; Ardavan, A; Porfyrakis, K; Lyon, S A; Briggs, G A D; Morton, John J. L.; Tyryshkin, Alexei M.; Ardavan, Arzhang; Porfyrakis, Kyriakos
2006-01-01
We examine environmental effects of surrounding nuclear spins on the electron spin relaxation of the N@C60 molecule (which consists of a nitrogen atom at the centre of a fullerene cage). Using dilute solutions of N@C60 in regular and deuterated toluene, we observe and model the effect of translational diffusion of nuclear spins of the solvent molecules on the N@C60 electron spin relaxation times. We also study spin relaxation in frozen solutions of N@C60 in CS2, to which small quantities of a glassing agent, S2Cl2 are added. At low temperatures, spin relaxation is caused by spectral diffusion of surrounding nuclear (35,37)Cl spins in the S2Cl2, but nevertheless, at 20 K, T2 times as long as 0.23 ms are observed
Yang, Shi-Peng; Lu, Mao-Wang; Huang, Xin-Hong; Tang, Qiang; Zhou, Yong-Long
2017-04-01
A theoretical study has been carried out on the spin-dependent electron transport in a hybrid magnetic-electric barrier nanostructure with both Rashba and Dresselhaus spin-orbit couplings, which can be experimentally realized by depositing a ferromagnetic strip and a Schottky metal strip on top of a semiconductor heterostructure. The spin-orbit coupling-dependent transmission coefficient, conductance, and spin polarization are calculated by solving the Schrödinger equation exactly with the help of the transfer-matrix method. We find that both the magnitude and sign of the electron spin polarization vary strongly with the spin-orbit coupling strength. Thus, the degree of electron spin polarization can be manipulated by properly adjusting the spin-orbit coupling strength, and such a nanosystem can be employed as a controllable spin filter for spintronics applications.
Simon, F; Dóra, B; Murányi, F; Jánossy, A; Garaj, S; Forró, L; Bud'ko, S; Petrovic, C; Canfield, P C
2008-10-24
The temperature dependence of the electron-spin relaxation time in MgB2 is anomalous as it does not follow the resistivity above 150 K; it has a maximum around 400 K and decreases for higher temperatures. This violates the well established Elliot-Yafet theory of spin relaxation in metals. The anomaly occurs when the quasiparticle scattering rate (in energy units) is comparable to the energy difference between the conduction and a neighboring bands. The anomalous behavior is related to the unique band structure of MgB2 and the large electron-phonon coupling. The saturating spin relaxation is the spin transport analogue of the Ioffe-Regel criterion of electron transport.
Spinning Carbon Nanotube Nanothread under a Scanning Electron Microscope
Mark Schulz
2011-08-01
Full Text Available Nanothread with a diameter as small as one hundred nanometers was manufactured under a scanning electron microscope. Made directly from carbon nanotubes, and inheriting their superior electrical and mechanical properties, nanothread may be the world’s smallest man-made fiber. The smallest thread that can be spun using a bench-top spinning machine is about 5 microns in diameter. Nanothread is a new material building block that can be used at the nanoscale or plied to form yarn for applications at the micro and macro scales. Preliminary electrical and mechanical properties of nanothread were measured. The resistivity of nanothread is less than 10−5 Ω∙m. The strength of nanothread is greater than 0.5 GPa. This strength was obtained from measurements using special glue that cures in an electron microscope. The glue weakened the thread, thus further work is needed to obtain more accurate measurements. Nanothread will have broad applications in enabling electrical components, circuits, sensors, and tiny machines. Yarn can be used for various macroscale applications including lightweight antennas, composites, and cables.
SU(2) Invariants of Symmetric Qubit States
Sirsi, Swarnamala
2011-01-01
Density matrix for N-qubit symmetric state or spin-j state (j = N/2) is expressed in terms of the well known Fano statistical tensor parameters. Employing the multiaxial representation [1], wherein a spin-j density matrix is shown to be characterized by j(2j+1) axes and 2j real scalars, we enumerate the number of invariants constructed out of these axes and scalars. These invariants are explicitly calculated in the particular case of pure as well as mixed spin-1 state.
Spin eigen-states of Dirac equation for quasi-two-dimensional electrons
Eremko, Alexander, E-mail: eremko@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Metrologichna Sttr., 14-b, Kyiv, 03680 (Ukraine); Brizhik, Larissa, E-mail: brizhik@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Metrologichna Sttr., 14-b, Kyiv, 03680 (Ukraine); Loktev, Vadim, E-mail: vloktev@bitp.kiev.ua [Bogolyubov Institute for Theoretical Physics, Metrologichna Sttr., 14-b, Kyiv, 03680 (Ukraine); National Technical University of Ukraine “KPI”, Peremohy av., 37, Kyiv, 03056 (Ukraine)
2015-10-15
Dirac equation for electrons in a potential created by quantum well is solved and the three sets of the eigen-functions are obtained. In each set the wavefunction is at the same time the eigen-function of one of the three spin operators, which do not commute with each other, but do commute with the Dirac Hamiltonian. This means that the eigen-functions of Dirac equation describe three independent spin eigen-states. The energy spectrum of electrons confined by the rectangular quantum well is calculated for each of these spin states at the values of energies relevant for solid state physics. It is shown that the standard Rashba spin splitting takes place in one of such states only. In another one, 2D electron subbands remain spin degenerate, and for the third one the spin splitting is anisotropic for different directions of 2D wave vector.
Du, Fang-Fang; Long, Gui-Lu
2017-01-01
We present a refined entanglement concentration protocol (ECP) for an arbitrary unknown less-entangled four-electron-spin cluster state by exploring the optical selection rules derived from the quantum-dot spins in one-sided optical microcavities. In our ECP, the parties obtain not only the four-electron-spin systems in the partial entanglement with two unknown parameters, but also the less-entangled two-electron-spin systems in the first step. Utilizing the above preserved systems as the resource for the second step of our ECP, the parties can obtain a standard cluster state by keeping the robust odd-parity instances with two parity-check gates. Meanwhile, the systems in the rest three instances can be used as the resource in the next round of our ECP. The success probability of our ECP is largely increased by iteration of the ECP process. Moreover, all the coefficients of our ECP are unknown for the parties without assistance of extra single electron-spin, so our ECP maybe has good applications in quantum communication network in the future.
Implementation of Universal Control on a Decoherence-Free Qubit
Fortunato, E M; Hodges, J; Teklemariam, G; Cory, D G; Fortunato, Evan M.; Viola, Lorenza; Hodges, Jonathan; Teklemariam, Grum; Cory, David G.
2001-01-01
We demonstrate storage and manipulation of one qubit encoded into a decoherence-free subspace (DFS) of two nuclear spins using liquid state nuclear magnetic resonance (NMR) techniques. The DFS is spanned by states that are unaffected by arbitrary collective phase noise. Encoding and decoding procedures reversibly map an arbitrary qubit state from a single data spin to the DFS and back. The implementation demonstrates the robustness of the DFS memory against engineered dephasing with arbitrary strength as well as a substantial increase in the amount of quantum information retained, relative to an un-encoded qubit, under both engineered and natural noise processes. In addition, a universal set of logical manipulations over the encoded qubit is also realized. Although intrinsic limitations prevent maintaining full noise tolerance during quantum gates, we show how the use of dynamical control methods at the encoded level can ensure that computation is protected with finite distance. We demonstrate noise-tolerant ...
Coupled superconducting flux qubits
Plantenberg, J.H.
2007-01-01
This thesis presents results of theoretical and experimental work on superconducting persistent-current quantum bits. These qubits offer an attractive route towards scalable solid-state quantum computing. The focus of this work is on the gradiometer flux qubit which has a special geometric design, t
Coupled superconducting flux qubits
Plantenberg, J.H.
2007-01-01
This thesis presents results of theoretical and experimental work on superconducting persistent-current quantum bits. These qubits offer an attractive route towards scalable solid-state quantum computing. The focus of this work is on the gradiometer flux qubit which has a special geometric design, t
Electron Spin-Lattice Relaxation of doped Yb3+ ions in YBa2Cu3Ox
2005-01-01
The electron spin-lattice relaxation (SLR) times T1 of Yb3+ ions were measured from the temperature dependence of electron spin resonance linewidth in Y0.99Yb0.01Ba2Cu3Ox with different oxygen contents. Raman relaxation processes dominate the electron SLR. Derived from the temperature dependence of the SLR rate, the Debye temperature (Td) increases with the critical temperature Tc and oxygen content x. Keywords: EPR; ESR; Electron spin-lattice relaxation; Debye temperature; Critical tem...
Shokeen, V.; Sanchez Piaia, M.; Bigot, J.-Y.; Müller, T.; Elliott, P.; Dewhurst, J. K.; Sharma, S.; Gross, E. K. U.
2017-09-01
A joint theoretical and experimental investigation is performed to understand the underlying physics of laser-induced demagnetization in Ni and Co films with varying thicknesses excited by 10 fs optical pulses. Experimentally, the dynamics of spins is studied by determining the time-dependent amplitude of the Voigt vector, retrieved from a full set of magnetic and nonmagnetic quantities performed on both sides of films, with absolute time reference. Theoretically, ab initio calculations are performed using time-dependent density functional theory. Overall, we demonstrate that spin-orbit induced spin flips are the most significant contributors with superdiffusive spin transport, which assumes only that the transport of majority spins without spin flips induced by scattering does not apply in Ni. In Co it plays a significant role during the first ˜20 fs only. Our study highlights the material dependent nature of the demagnetization during the process of thermalization of nonequilibrium spins.
Likhtenshtein, Gertz
2016-01-01
This book presents the versatile and pivotal role of electron spin interactions in nature. It provides the background, methodologies and tools for basic areas related to spin interactions, such as spin chemistry and biology, electron transfer, light energy conversion, photochemistry, radical reactions, magneto-chemistry and magneto-biology. The book also includes an overview of designing advanced magnetic materials, optical and spintronic devices and photo catalysts. This monograph appeals to scientists and graduate students working in the areas related to spin interactions physics, biophysics, chemistry and chemical engineering.
Coherence transfer and electron T1-, T2-relaxation in nitroxide spin labels
Marsh, Derek
2017-01-01
Abragam's double-commutator spin operator method is used to analyse: 1) electron coherence transfer by intermolecular dipolar interaction between spin-label radicals, and 2) longitudinal and transverse electron spin relaxation by rotational modulation of the Zeeman and nitrogen-hyperfine anisotro......Abragam's double-commutator spin operator method is used to analyse: 1) electron coherence transfer by intermolecular dipolar interaction between spin-label radicals, and 2) longitudinal and transverse electron spin relaxation by rotational modulation of the Zeeman and nitrogen......-hyperfine anisotropies of isolated nitroxide spin labels. Results compatible with earlier treatments by Redfield theory are obtained without specifically evaluating matrix elements. Extension to single-transition operators for isolated nitroxides predicts electron coherence transfer by pseudosecular electron......-nuclear dipolar interaction, in the absence of intermolecular dipolar coupling. This explains earlier experimental findings that coherence transfer (specifically dispersion-like distortion of the EPR absorption line shape) does not extrapolate to zero at low concentrations of nitroxide spin labels....
Manipulation of qubits in nonorthogonal collective storage modes
Refsgaard, Jonas; Mølmer, Klaus
2012-01-01
We present an analysis of transfer of quantum information between the collective spin degrees of freedom of a large ensemble of two-level systems and a single central qubit. The coupling between the central qubit and the individual ensemble members may be varied and thus provides access to more...... than a single storage mode. Means to store and manipulate several independent qubits are derived for the case where the variation in coupling strengths does not allow addressing orthogonal modes of the ensemble. While our procedures and analysis may apply to a number of different physical systems...
Blank, Aharon; Shklyar, Roman; Twig, Ygal
2013-01-01
Spin-based quantum computation (QC) in the solid state is considered to be one of the most promising approaches to scalable quantum computers. However, it faces problems such as initializing the spins, selectively addressing and manipulating single spins, and reading out the state of the individual spins. We have recently sketched a scheme that potentially solves all of these problems5. This is achieved by making use of a unique phosphorus-doped 28Si sample (28Si:P), and applying powerful new electron spin resonance (ESR) techniques for parallel excitation, detection, and imaging in order to implement QCs and efficiently obtain their results. The beauty of our proposed scheme is that, contrary to other approaches, single-spin detection sensitivity is not required and a capability to measure signals of ~100-1000 spins is sufficient to implement it. Here we take the first experimental step towards the actual implementation of such scheme. We show that, by making use of the smallest ESR resonator constructed to ...
Electron spin and the origin of Bio-homochirality I. Extant enzymatic reaction model
Wang, Wei
2013-01-01
In this paper, I tentatively put forward a new hypothesis that the emergence of a single chiral form of biomolecules in living organisms is specifically determined by the electron spin state during their enzyme-catalyzed synthesis processes. Specifically speaking, the electrons released from the coenzyme NAD(P)H of amino acid synthase are heterogeneous in spin states; however, when they pass through the chiral alpha-helix structure of the enzymes to the site of amino acid synthesis at the other end of the helix, their spin states are filtered and polarized, producing only spin up electrons; once the spin-polarized electrons participate in the reductive reaction between alpha-oxo acid and ammonia, only L-amino acids are formed according to the Pauli exclusion principle.
Concept of a multichannel spin-resolving electron analyzer based on Mott scattering
Strocov, Vladimir N., E-mail: vladimir.strocov@psi.ch [Paul Scherrer Institute, CH-5232 Villigen-PSI (Switzerland); Petrov, Vladimir N. [St Petersburg Polytechnical University, Polytechnicheskaya Str. 29, St Petersburg RU-195251 (Russian Federation); Dil, J. Hugo [Paul Scherrer Institute, CH-5232 Villigen-PSI (Switzerland); École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne (Switzerland)
2015-04-10
The concept of a two-dimensional multichannel electron spin detector based on Mott scattering and imaging-type electron optics is presented. The efficiency increase of about four orders of magnitude opens new scientific fields including buried magnetic interfaces. The concept of a multichannel electron spin detector based on optical imaging principles and Mott scattering (iMott) is presented. A multichannel electron image produced by a standard angle-resolving (photo) electron analyzer or microscope is re-imaged by an electrostatic lens at an accelerating voltage of 40 kV onto the Au target. Quasi-elastic electrons bearing spin asymmetry of the Mott scattering are imaged by magnetic lenses onto position-sensitive electron CCDs whose differential signals yield the multichannel spin asymmetry image. Fundamental advantages of this concept include acceptance of inherently divergent electron sources from the electron analyzer or microscope focal plane as well as small aberrations achieved by virtue of high accelerating voltages, as demonstrated by extensive ray-tracing analysis. The efficiency gain compared with the single-channel Mott detector can be a factor of more than 10{sup 4} which opens new prospects of spin-resolved spectroscopies in application not only to standard bulk and surface systems (Rashba effect, topological insulators, etc.) but also to buried heterostructures. The simultaneous spin detection combined with fast CCD readout enables efficient use of the iMott detectors at X-ray free-electron laser facilities.
Spin-Orbit Coupling and Novel Electronic States at the Interfaces of Heavy Fermion Materials
2016-02-22
spin-orbit coupling (SOC) may induce new electronic phases that are difficult to realize in bulk materials . With the support of this STIR grant, we have...Report: Spin-Orbit Coupling and Novel Electronic States at the Interfaces of Heavy Fermion Materials Report Title This report summarizes the progress...regime in the correlated- electron “global” phase diagram of heavy fermion materials and, in addition, paving the way for interactions between the
Two dimensional electron spin resonance: Structure and dynamics of biomolecules
Saxena, Sunil; Freed, Jack H.
1998-03-01
The potential of two dimensional (2D) electron spin resonance (ESR) for measuring the structural properties and slow dynamics of labeled biomolecules will be presented. Specifically, it will be shown how the recently developed method of double quantum (DQ) 2D ESR (S. Saxena and J. H. Freed, J. Chem. Phys. 107), 1317, (1997) can be used to measure large interelectron distances in bilabeled peptides. The need for DQ ESR spectroscopy, as well as the challenges and advantages of this method will be discussed. The elucidation of the slow reorientational dynamics of this peptide (S. Saxena and J. H. Freed, J. Phys. Chem. A, 101) 7998 (1997) in a glassy medium using COSY and 2D ELDOR ESR spectroscopy will be demonstrated. The contributions to the homogeneous relaxation time, T_2, from the overall and/or internal rotations of the nitroxide can be distinguished from the COSY spectrum. The growth of spectral diffusion cross-peaks^2 with mixing time in the 2D ELDOR spectra can be used to directly determine a correlation time from the experiment which can be related to the rotational correlation time.
Mechanical detection of electron spin resonance beyond 1 THz
Takahashi, Hideyuki [Organization of Advanced Science and Technology, Kobe University, 1-1, Rokkodai, Nada, Kobe 657-8501 (Japan); Ohmichi, Eiji [Graduate School of Science, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501 (Japan); Ohta, Hitoshi [Molecular Photoscience Research Center, Kobe University, 1-1 Rokkodai-cho, Nada, Kobe 657-8501 (Japan)
2015-11-02
We report the cantilever detection of electron spin resonance (ESR) in the terahertz (THz) region. This technique mechanically detects ESR as a change in magnetic torque that acts on the cantilever. The ESR absorption of a tiny single crystal of Co Tutton salt, Co(NH{sub 4}){sub 2}(SO{sub 4}){sub 2}⋅6H{sub 2}O, was observed in frequencies of up to 1.1 THz using a backward travelling wave oscillator as a THz-wave source. This is the highest frequency of mechanical detection of ESR till date. The spectral resolution was evaluated with the ratio of the peak separation to the sum of the half-width at half maximum of two absorption peaks. The highest resolution value of 8.59 ± 0.53 was achieved at 685 GHz, while 2.47 ± 0.01 at 80 GHz. This technique will not only broaden the scope of ESR spectroscopy application but also lead to high-spectral-resolution ESR imaging.
Coherence preservation of a qubit inflicted by classical non-Gaussian charge noise
Ramon, Guy
2015-03-01
The efficiency of decoupling pulse sequences in removing noise due to several charge fluctuators is studied. Both numerical simulations and analytics are used to explore the qubit's dephasing and dissipative dynamics. Special emphasis is placed on qubit dynamics at the optimal point, where it is found that fluctuators that are strongly coupled to the qubit induce a non-Gaussian noise. Exact analytical results for this limit reveal a nontrivial scaling of the noise with the number of fluctuators. Furthermore, a crossover between distinct qubit dynamics is demonstrated by increasing the number of control pulses and/or varying the qubit's working position. While we consider as a test case exchange-coupled spin qubits in gate-defined GaAs double dots, our results are relevant to other systems such as superconducting Josephson qubits, and Si/SiGe quantum dots. Supported by NSF Grant DMR-1207298.
Coupling of spin and orbital motion of electrons in carbon nanotubes
Kuemmeth, Ferdinand; Ilani, S; Ralph, D C;
2008-01-01
Electrons in atoms possess both spin and orbital degrees of freedom. In non-relativistic quantum mechanics, these are independent, resulting in large degeneracies in atomic spectra. However, relativistic effects couple the spin and orbital motion, leading to the well-known fine structure...... in their spectra. The electronic states in defect-free carbon nanotubes are widely believed to be four-fold degenerate, owing to independent spin and orbital symmetries, and also to possess electron–hole symmetry. Here we report measurements demonstrating that in clean nanotubes the spin and orbital motion...... and antiparallel alignment for holes. Our measurements are consistent with recent theories that predict the existence of spin–orbit coupling in curved graphene and describe it as a spin dependent topological phase in nanotubes. Our findings have important implications for spin-based applications in carbon- based...
Scaling of dynamical decoupling for a single electron spin in nanodiamonds at room temperature
Liu, Dong-Qi; Liu, Gang-Qin; Chang, Yan-Chun; Pan, Xin-Yu
2014-01-01
Overcoming the spin qubit decoherence is a challenge for quantum science and technology. We investigate the decoherence process in nanodiamonds by Carr-Purcell-Meiboom-Gill (CPMG) technique at room temperature. We find that the coherence time T2 scales as nγ. The elongation effect of coherence time can be represented by a constant power of the number of pulses n. Considering the filter function of CPMG decoupling sequence as a δ function, the spectrum density of noise has been reconstructed directly from the coherence time measurements and a Lorentzian noise power spectrum model agrees well with the experiment. These results are helpful for the application of nanodiamonds to nanoscale magnetic imaging.
Aharony, Amnon; Tokura, Yasuhiro; Cohen, Guy Z.; Entin-Wohlman, Ora; Katsumoto, Shingo
2011-07-01
Spin-1/2 electrons are scattered through one or two diamond-like loops, made of quantum dots connected by one-dimensional wires, and subject to both an Aharonov-Bohm flux and (Rashba and Dresselhaus) spin-orbit interactions. With some symmetry between the two branches of each diamond, and with appropriate tuning of the electric and magnetic fields (or of the diamond shapes), this device completely blocks electrons with one polarization and allows only electrons with the opposite polarization to be transmitted. The directions of these polarizations are tunable by these fields, and do not depend on the energy of the scattered electrons. For each range of fields one can tune the site and bond energies of the device so that the transmission of the fully polarized electrons is close to unity. Thus, these devices perform as ideal spin filters, and these electrons can be viewed as mobile qubits; the device writes definite quantum information on the spinors of the outgoing electrons. The device can also read the information written on incoming polarized electrons: The charge transmission through the device contains full information on this polarization. The double-diamond device can also act as a realization of the Datta-Das spin field-effect transistor.
Hydrogenic spin quantum computing in silicon, and, Damping and diffusion in a chain-boson model
Skinner, Andrew J.
2006-12-01
We propose an architecture for quantum computing with spin-pair encoded qubits in silicon. Electron-nuclear spin-pairs are controlled by a DC magnetic field and electrode-switched on and off hyperfine interaction. This digital processing is insensitive to tuning errors and easy to model. Electron shuttling between donors enables multi-qubit logic. These hydrogenic spin qubits are transferable to nuclear spin-pairs, which have long coherence times, and electron spin-pairs, which are ideally suited for measurement and initialization. The architecture is scaleable to highly parallel operation. We also study the open-system dynamics of a few two-level systems coupled together and embedded in a crystal lattice. In one case, superconducting quantum interference devices, or SQUIDs, exchange their angular momenta with the lattice. Some decaying oscillations can emerge in a lower energy subspace with a longer coherence time. In another case, the exchange coupling between spins-1/2 is strained by lattice distortions. At a critical point energy level crossing, four well-spaced spins dissipate collectively. This is partially true also for the two- or three-SQUID-chain. These collective couplings can improve coherence times.
Heat transport and electron cooling in ballistic normal-metal/spin-filter/superconductor junctions
Kawabata, Shiro, E-mail: s-kawabata@aist.go.jp [Electronics and Photonics Research Institute (ESPRIT), National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Ibaraki 305-8568 (Japan); Vasenko, Andrey S. [LPMMC, Université Joseph Fourier and CNRS, 25 Avenue des Martyrs, BP 166, 38042 Grenoble (France); Ozaeta, Asier [Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Manuel de Lardizabal 5, E-20018 San Sebastián (Spain); Bergeret, Sebastian F. [Centro de Física de Materiales (CFM-MPC), Centro Mixto CSIC-UPV/EHU, Manuel de Lardizabal 5, E-20018 San Sebastián (Spain); Donostia International Physics Center (DIPC), Manuel de Lardizabal 5, E-20018 San Sebastián (Spain); Hekking, Frank W.J. [LPMMC, Université Joseph Fourier and CNRS, 25 Avenue des Martyrs, BP 166, 38042 Grenoble (France)
2015-06-01
We investigate electron cooling based on a clean normal-metal/spin-filter/superconductor junction. Due to the suppression of the Andreev reflection by the spin-filter effect, the cooling power of the system is found to be extremely higher than that for conventional normal-metal/nonmagnetic-insulator/superconductor coolers. Therefore we can extract large amount of heat from normal metals. Our results strongly indicate the practical usefulness of the spin-filter effect for cooling detectors, sensors, and quantum bits.
Proposed coupling of an electron spin in a semiconductor quantum dot to a nanosize optical cavity.
Majumdar, Arka; Kaer, Per; Bajcsy, Michal; Kim, Erik D; Lagoudakis, Konstantinos G; Rundquist, Armand; Vučković, Jelena
2013-07-12
We propose a scheme to efficiently couple a single quantum dot electron spin to an optical nano-cavity, which enables us to simultaneously benefit from a cavity as an efficient photonic interface, as well as to perform high fidelity (nearly 100%) spin initialization and manipulation achievable in bulk semiconductors. Moreover, the presence of the cavity speeds up the spin initialization process beyond the GHz range.
Ivantsov, Ilya; Ferraz, Alvaro; Kochetov, Evgenii
2016-01-01
We perform quantum Monte Carlo simulations of the itinerant-localized periodic Kondo-Heisenberg model for the underdoped cuprates to calculate the associated spin correlation functions. The strong electron correlations are shown to play a key role in the abrupt destruction of the quasi long-range antiferromagnetic order in the lightly doped regime.
Ivantsov, Ilya; Ferraz, Alvaro; Kochetov, Evgenii
2016-12-01
We perform quantum Monte Carlo simulations of the itinerant-localized periodic Kondo-Heisenberg model for the underdoped cuprates to calculate the associated spin correlation functions. The strong electron correlations are shown to play a key role in the abrupt destruction of the quasi-long-range antiferromagnetic order in the lightly doped regime.
Picture change error in quasirelativistic electron/spin density, Laplacian and bond critical points
Bučinský, Lukáš
2014-06-01
The change of picture of the quasirelativistic Hartree-Fock wave functions is considered for electron/spin densities, the negative Laplacian of electron density and the appropriate bond critical point characteristics from the Quantum Theory of Atoms In Molecules (QTAIM). [OsCl5(Hpz)]- and [RuCl5(NO)]2- transition metal complexes are considered. Both, scalar relativistic and spin-orbit effects have been accounted for using the Infinite Order Two Component (IOTC) Hamiltonian. Picture change error (PCE) correction in the electron and spin densities and the Laplacian of electron density are treated analytically. Generally, PCE is found significant only in the core region of the atoms for the electron/spin density as well as Laplacian.©2014 Elsevier B.V. All rights reserved.
Spin-Orbit Coupling Controlled J =3 /2 Electronic Ground State in 5 d3 Oxides
Taylor, A. E.; Calder, S.; Morrow, R.; Feng, H. L.; Upton, M. H.; Lumsden, M. D.; Yamaura, K.; Woodward, P. M.; Christianson, A. D.
2017-05-01
Entanglement of spin and orbital degrees of freedom drives the formation of novel quantum and topological physical states. Here we report resonant inelastic x-ray scattering measurements of the transition metal oxides Ca3 LiOsO6 and Ba2 YOsO6 , which reveals a dramatic spitting of the t2 g manifold. We invoke an intermediate coupling approach that incorporates both spin-orbit coupling and electron-electron interactions on an even footing and reveal that the ground state of 5 d3-based compounds, which has remained elusive in previously applied models, is a novel spin-orbit entangled J =3 /2 electronic ground state. This work reveals the hidden diversity of spin-orbit controlled ground states in 5 d systems and introduces a new arena in the search for spin-orbit controlled phases of matter.
Observation of vacuum-enhanced electron spin resonance of levitated nanodiamonds
Hoang, Thai M; Bang, Jaehoon; Li, Tongcang
2015-01-01
Electron spins of diamond nitrogen-vacancy (NV) centers are important quantum resources for nanoscale sensing and quantum information. Combining such NV spin systems with levitated optomechanical resonators will provide a hybrid quantum system for many novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centers in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this novel system, we also investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect. Our results show that optical levitation of nanodiamonds in vacuum not only can improve the mechanical quality of its oscillation, but also enhance the ESR contrast, which pave the way towards a novel levitated spin-optomechanical system for studying macroscopic quantum mechanics. The results also indicate potenti...
Observation of vacuum-enhanced electron spin resonance of optically levitated nanodiamonds
Li, Tongcang; Hoang, Thai; Ahn, Jonghoon; Bang, Jaehoon
Electron spins of diamond nitrogen-vacancy (NV) centers are important quantum resources for nanoscale sensing and quantum information. Combining such NV spin systems with levitated optomechanical resonators will provide a hybrid quantum system for many novel applications. Here we optically levitate a nanodiamond and demonstrate electron spin control of its built-in NV centers in low vacuum. We observe that the strength of electron spin resonance (ESR) is enhanced when the air pressure is reduced. To better understand this novel system, we also investigate the effects of trap power and measure the absolute internal temperature of levitated nanodiamonds with ESR after calibration of the strain effect. Our results show that optical levitation of nanodiamonds in vacuum not only can improve the mechanical quality of its oscillation, but also enhance the ESR contrast, which pave the way towards a novel levitated spin-optomechanical system for studying macroscopic quantum mechanics. The results also indicate potential applications of NV centers in gas sensing.
The surface magnetization study of Cr2O3 by spin polarized low energy electron microscopy
Cao, Shi; Wu, Ning; Zhang, Xin; N'diaye, Alpha; Chen, Gong; Schmid, Andreas; Echtenkamp, Will; Lauter, Valeria; Binek, Christian; Dowben, Peter
2014-03-01
The boundary magnetization at the surface of a Cr2O3 single crystal has been demonstrated by using spin-polarized low-energy electron microscopy (SPLEEM), indicating net surface spin polarization. This work shows that the placement of Cr2O3 single crystal in the single domain state, will result in net Cr2O3 spin polarization at the boundary, even in the presence of a gold overlayer. There are indications that the spin-polarized low-energy electron microscopy (SPLEEM) contrast for the two polarizations states is different. In addition, the boundary magnetization protected by the symmetry exists despite of the surface roughness/softness which was studied by the non-spin neutron reflectometry and low energy electron diffraction. Unoccupied surface oxygen sites and chromium sites are possible mechanism contributing to the surface ``softness,'' which will be discussed.
Nanosecond-timescale spin transfer using individual electrons in a quadruple-quantum-dot device
Baart, T. A.; Jovanovic, N.; Vandersypen, L. M. K. [QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Reichl, C.; Wegscheider, W. [Solid State Physics Laboratory, ETH Zürich, 8093 Zürich (Switzerland)
2016-07-25
The ability to coherently transport electron-spin states between different sites of gate-defined semiconductor quantum dots is an essential ingredient for a quantum-dot-based quantum computer. Previous shuttles using electrostatic gating were too slow to move an electron within the spin dephasing time across an array. Here, we report a nanosecond-timescale spin transfer of individual electrons across a quadruple-quantum-dot device. Utilizing enhanced relaxation rates at a so-called hot spot, we can upper bound the shuttle time to at most 150 ns. While actual shuttle times are likely shorter, 150 ns is already fast enough to preserve spin coherence in, e.g., silicon based quantum dots. This work therefore realizes an important prerequisite for coherent spin transfer in quantum dot arrays.
Direct Measurement of the Flip-Flop Rate of Electron Spins in the Solid State
Dikarov, Ekaterina; Zgadzai, Oleg; Artzi, Yaron; Blank, Aharon
2016-10-01
Electron spins in solids have a central role in many current and future spin-based devices, ranging from sensitive sensors to quantum computers. Many of these apparatuses rely on the formation of well-defined spin structures (e.g., a 2D array) with controlled and well-characterized spin-spin interactions. While being essential for device operation, these interactions can also result in undesirable effects, such as decoherence. Arguably, the most important pure quantum interaction that causes decoherence is known as the "flip-flop" process, where two interacting spins interchange their quantum state. Currently, for electron spins, the rate of this process can only be estimated theoretically, or measured indirectly, under limiting assumptions and approximations, via spin-relaxation data. This work experimentally demonstrates how the flip-flop rate can be directly and accurately measured by examining spin-diffusion processes in the solid state for physically fixed spins. Under such terms, diffusion can occur only through this flip-flop-mediated quantum-state exchange and not via actual spatial motion. Our approach is implemented on two types of samples, phosphorus-doped 28Si and nitrogen vacancies in diamond, both of which are significantly relevant to quantum sensors and information processing. However, while the results for the former sample are conclusive and reveal a flip-flop rate of approximately 12.3 Hz, for the latter sample only an upper limit of approximately 0.2 Hz for this rate can be estimated.
Coupling of spin and orbital motion of electrons in carbon nanotubes
Kuemmeth, Ferdinand; Ilani, S; Ralph, D C
2008-01-01
Electrons in atoms possess both spin and orbital degrees of freedom. In non-relativistic quantum mechanics, these are independent, resulting in large degeneracies in atomic spectra. However, relativistic effects couple the spin and orbital motion, leading to the well-known fine structure in their......Electrons in atoms possess both spin and orbital degrees of freedom. In non-relativistic quantum mechanics, these are independent, resulting in large degeneracies in atomic spectra. However, relativistic effects couple the spin and orbital motion, leading to the well-known fine structure...... in their spectra. The electronic states in defect-free carbon nanotubes are widely believed to be four-fold degenerate, owing to independent spin and orbital symmetries, and also to possess electron–hole symmetry. Here we report measurements demonstrating that in clean nanotubes the spin and orbital motion...... of electrons are coupled, thereby breaking all of these symmetries. This spin–orbit coupling is directly observed as a splitting of the four-fold degeneracy of a single electron in ultra-clean quantum dots. The coupling favours parallel alignment of the orbital and spin magnetic moments for electrons...
Jeong, Min Sook; Yu, Kyeong-Nam; Chung, Hyun Hoon; Park, Soo Jin; Lee, Ah Young; Song, Mi Ryoung; Cho, Myung-Haing; Kim, Jun Sung
2016-05-01
Qualitative and quantitative analyses of reactive oxygen species (ROS) generated on the surfaces of nanomaterials are important for understanding their toxicity and toxic mechanisms, which are in turn beneficial for manufacturing more biocompatible nanomaterials in many industrial fields. Electron spin resonance (ESR) is a useful tool for detecting ROS formation. However, using this technique without first considering the physicochemical properties of nanomaterials and proper conditions of the spin trapping agent (such as incubation time) may lead to misinterpretation of the resulting data. In this report, we suggest methodological considerations for ESR as pertains to magnetism, sample preparation and proper incubation time with spin trapping agents. Based on our results, each spin trapping agent should be given the proper incubation time. For nanomaterials having magnetic properties, it is useful to remove these nanomaterials via centrifugation after reacting with spin trapping agents. Sonication for the purpose of sample dispersion and sample light exposure should be controlled during ESR in order to enhance the obtained ROS signal. This report will allow researchers to better design ESR spin trapping applications involving nanomaterials.
Delayed entanglement echo for individual control of a large number of nuclear spins
Wang, Zhen-Yu; Casanova, Jorge; Plenio, Martin B.
2017-03-01
Methods to selectively detect and manipulate nuclear spins by single electrons of solid-state defects play a central role for quantum information processing and nanoscale nuclear magnetic resonance (NMR). However, with standard techniques, no more than eight nuclear spins have been resolved by a single defect centre. Here we develop a method that improves significantly the ability to detect, address and manipulate nuclear spins unambiguously and individually in a broad frequency band by using a nitrogen-vacancy (NV) centre as model system. On the basis of delayed entanglement control, a technique combining microwave and radio frequency fields, our method allows to selectively perform robust high-fidelity entangling gates between hardly resolved nuclear spins and the NV electron. Long-lived qubit memories can be naturally incorporated to our method for improved performance. The application of our ideas will increase the number of useful register qubits accessible to a defect centre and improve the signal of nanoscale NMR.
Tsuchimochi, Takashi; Ten-No, Seiichiro
2017-04-11
We propose a size-consistent generalization of the recently developed spin-extended configuration interaction with singles and doubles (ECISD), where a CI wave function is explicitly spin-projected. The size-consistent effect is effectively incorporated by treating quadruples within the formulation of coupled electron pair approximation. As in coupled-cluster theory, quadruple excitations are approximated by a disconnected product of double excitations. Despite its conceptual similarity to the standard single-reference and multireference analogues, such a generalization requires careful derivation, as the spin-projected CI space is nonorthogonal and overcomplete. Although our methods generally yield better results than ECISD, size-consistency is only approximately retained because the action of a symmetry-projection operator is size-inconsistent. In this work, we focus on simple models where exclusion-principle-violating terms, which eliminate undesired contributions to the correlation effects, are either completely neglected or averaged. These models possess an orbital-invariant energy functional that is to be minimized by diagonalizing an energy-shifted effective Hamiltonian within the singles and doubles manifold. This allows for a straightforward generalization of the ECISD analytical gradients needed to determine molecular properties and geometric optimization. Given the multireference nature of the spin-projected Hartree-Fock method, the proposed approaches are expected to handle static correlation, unlike single-reference analogues. We critically assess the performance of our methods using dissociation curves of molecules, singlet-triplet splitting gaps, hyperfine coupling constants, and the chromium dimer. The size-consistency and size-extensivity of the methods are also discussed.
Gorcester, Jeff; Rananavare, Shankar B.; Freed, Jack H.
1989-05-01
Electron spin-echo (ESE) and two-dimensional electron-electron double resonance (2D ELDOR) experiments have been performed as a function of director orientation and temperature in the smectic A phase of the liquid crystal S2 for the spin-probe PD-tempone(2×10-3 M). Over the entire temperature range studied (288-323 K) we observe significant 2D ELDOR cross peaks only for ΔMI =±1 indicative of 14N spin-relaxation and negligible Heisenberg exchange. From the angular dependent 14N spin-relaxation rates we obtain the dipolar spectral densities at the hyperfine (hf) frequency, whereas from a combination of ESE and 2D ELDOR we obtain the dipolar and Zeeman-dipolar spectral densities at zero frequency. The angular dependent spectral densities were successfully decomposed into their basic components in accordance with theory. The angular dependent spectral densities at the hf frequency are not predicted by a model of anisotropic rotational diffusion in a nematic orienting potential, but are consistent with predictions of a model due to Moro and Nordio of solute rototranslational diffusion in a McMillan-type potential. The angular dependence also indicates that order director fluctuations in the smectic phase are suppressed at frequencies on the order of 10 MHz. An additional contribution to solute reorientation due to cooperative hydrocarbon chain fluctuations is suggested to account for the behavior of the observed spectral densities at zero frequency. An evaluation of the relevance of several other dynamical models to this experimental work is also presented.
Proposed Coupling of an Electron Spin in a Semiconductor Quantum Dot to a Nanosize Optical Cavity
Majumdar, Arka; Nielsen, Per Kær; Bajcsy, Michal
2013-01-01
We propose a scheme to efficiently couple a single quantum dot electron spin to an optical nano-cavity, which enables us to simultaneously benefit from a cavity as an efficient photonic interface, as well as to perform high fidelity (nearly 100%) spin initialization and manipulation achievable in...
Electron spin relaxation can enhance the performance of a cryptochrome-based magnetic compass sensor
Kattnig, Daniel R; Sowa, Jakub K; Solov'yov, Ilia A;
2016-01-01
The radical pair model of the avian magnetoreceptor relies on long-lived electron spin coherence. Dephasing, resulting from interactions of the spins with their fluctuating environment, is generally assumed to degrade the sensitivity of this compass to the direction of the Earth's magnetic field...
Electron Spin Resonance and Related Phenomena in Low-Dimensional Structures
Fanciulli, Marco
2009-01-01
Deals with the discussion of the development of spin resonance in low dimensional structures, such as two-dimensional electron systems, quantum wires, and quantum dots. This title discusses opportunities for spin resonance techniques, with emphasis on fundamental physics, nanoelectronics, spintronics, and quantum information processing
Danon, J.; Nazarov, Y.V.
2008-01-01
We study nuclear spin dynamics in a quantum dot close to the conditions of electron spin resonance. We show that at a small frequency mismatch, the nuclear field detunes the resonance. Remarkably, at larger frequency mismatch, its effect is opposite: The nuclear system is bistable, and in one of the
Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation
Srinivasa Rao Singamaneni
2014-04-01
Full Text Available Electronic spin transport properties of graphene nanoribbons (GNRs are influenced by the presence of adatoms, adsorbates and edge functionalization. To improve the understanding of the factors that influence the spin properties of GNRs, local (element spin-sensitive techniques such as electron spin resonance (ESR spectroscopy are important for spintronics applications. Here, we present results of multi-frequency continuous wave (CW, pulse and hyperfine sublevel correlation (HYSCORE ESR spectroscopy measurements performed on oxidatively unzipped graphene nanoribbons (GNRs, which were subsequently chemically converted (CCGNRs with hydrazine. ESR spectra at 336 GHz reveal an isotropic ESR signal from the CCGNRs, of which the temperature dependence of its line width indicates the presence of localized unpaired electronic states. Upon functionalization of CCGNRs with 4-nitrobenzene diazonium tetrafluoroborate, the ESR signal is found to be 2 times narrower than that of pristine ribbons. NH3 adsorption/desorption on CCGNRs is shown to narrow the signal, while retaining the signal intensity and g value. The electron spin-spin relaxation process at 10 K is found to be characterized by slow (163 ns and fast (39 ns components. HYSCORE ESR data demonstrate the explicit presence of protons and 13C atoms. With the provided identification of intrinsic point magnetic defects such as proton and 13C has been reported, which are roadblocks to spin travel in graphene-based materials, this work could help in advancing the present fundamental understanding on the edge-spin (or magnetic-based transport properties of CCGNRs.
Magnetic defects in chemically converted graphene nanoribbons: electron spin resonance investigation
Singamaneni, Srinivasa Rao, E-mail: ssingam@ncsu.edu [INPAC – Institute for Nanoscale Physics and Chemistry, Semiconductor Physics Laboratory, K.U. Leuven, Celestijnenlaan 200D, B–3001 Leuven (Belgium); Materials Science Division, Army Research Office, Research Triangle Park, North Carolina 27709 (United States); Department of Material Science and Engineering, North Carolina State University, Raleigh, North Carolina 27695 (United States); Stesmans, Andre [INPAC – Institute for Nanoscale Physics and Chemistry, Semiconductor Physics Laboratory, K.U. Leuven, Celestijnenlaan 200D, B–3001 Leuven (Belgium); Tol, Johan van [National High Magnetic Field Laboratory, Florida State University, 1800 E. Paul Dirac Drive, Tallahassee, Florida 32310 (United States); Kosynkin, D. V. [Department of Chemistry, Smalley Institute for Nanoscale Science and Technology, Rice University, MS-222, 6100 Main Street, Houston, Texas 77005 (United States); Tour, James M. [Department of Chemistry, Smalley Institute for Nanoscale Science and Technology, Rice University, MS-222, 6100 Main Street, Houston, Texas 77005 (United States); Department of Mechanical Engineering and Materials Science, Smalley Institute for Nanoscale Science and Technology, Rice University, MS-222, 6100 Main Street, Houston, Texas 77005 (United States); Smalley Institute for Nanoscale Science and Technology, Rice University, MS-222, 6100 Main Street, Houston, Texas 77005, USA. (United States)
2014-04-15
Electronic spin transport properties of graphene nanoribbons (GNRs) are influenced by the presence of adatoms, adsorbates and edge functionalization. To improve the understanding of the factors that influence the spin properties of GNRs, local (element) spin-sensitive techniques such as electron spin resonance (ESR) spectroscopy are important for spintronics applications. Here, we present results of multi-frequency continuous wave (CW), pulse and hyperfine sublevel correlation (HYSCORE) ESR spectroscopy measurements performed on oxidatively unzipped graphene nanoribbons (GNRs), which were subsequently chemically converted (CCGNRs) with hydrazine. ESR spectra at 336 GHz reveal an isotropic ESR signal from the CCGNRs, of which the temperature dependence of its line width indicates the presence of localized unpaired electronic states. Upon functionalization of CCGNRs with 4-nitrobenzene diazonium tetrafluoroborate, the ESR signal is found to be 2 times narrower than that of pristine ribbons. NH{sub 3} adsorption/desorption on CCGNRs is shown to narrow the signal, while retaining the signal intensity and g value. The electron spin-spin relaxation process at 10 K is found to be characterized by slow (163 ns) and fast (39 ns) components. HYSCORE ESR data demonstrate the explicit presence of protons and {sup 13}C atoms. With the provided identification of intrinsic point magnetic defects such as proton and {sup 13}C has been reported, which are roadblocks to spin travel in graphene-based materials, this work could help in advancing the present fundamental understanding on the edge-spin (or magnetic)-based transport properties of CCGNRs.
Mitrikas, George; Papavassiliou, Georgios
2009-01-01
Since the idea of quantum information processing (QIP) fascinated the scientific community, electron and nuclear spins have been regarded as promising candidates for quantum bits (qubits). A fundamental challenge in the realization of a solid-state quantum computer is the construction of fast and reliable two-qubit quantum gates. Of particular interest in this direction are hybrid systems of electron and nuclear spins, where the two qubits are coupled through the hyperfine interaction. However, the significantly different gyromagnetic ratios of electron and nuclear spins do not allow for their coherent manipulation at the same time scale. Here we demonstrate the control of the alpha-proton nuclear spin, I=1/2, coupled to the stable radical CH(COOH)2, S=1/2, in a gamma-irradiated malonic acid single crystal using only microwave pulses. We show that, depending on the state of the electron spin (mS=+1/2 or -1/2), the nuclear spin can be locked in a desired state or oscillate between mI=+1/2 and mI=-1/2 on the na...
Exact solution of qubit decoherence models by a transfer matrix method
Nghiem, D; Joynt, Robert; Nghiem, Diu
2005-01-01
We present a new method for the solution of the behavior of an enesemble of qubits in a random time-dependent external field. The forward evolution in time is governed by a transfer matrix. The elements of this matrix determine the various decoherence times. The method provides an exact solution in cases where the noise is piecewise constant in time. We show that it applies, for example, to a realistic model of decoherence of electron spins in semiconductors. Results are obtained for the non-perturbative regimes of the models, and we see a transition from weak relaxation to overdamped behavior as a function of noise anisotropy.
All-optical control of a solid-state spin using coherent dark states.
Yale, Christopher G; Buckley, Bob B; Christle, David J; Burkard, Guido; Heremans, F Joseph; Bassett, Lee C; Awschalom, David D
2013-05-07
The study of individual quantum systems in solids, for use as quantum bits (qubits) and probes of decoherence, requires protocols for their initialization, unitary manipulation, and readout. In many solid-state quantum systems, these operations rely on disparate techniques that can vary widely depending on the particular qubit structure. One such qubit, the nitrogen-vacancy (NV) center spin in diamond, can be initialized and read out through its special spin-selective intersystem crossing, while microwave electron spin resonance techniques provide unitary spin rotations. Instead, we demonstrate an alternative, fully optical approach to these control protocols in an NV center that does not rely on its intersystem crossing. By tuning an NV center to an excited-state spin anticrossing at cryogenic temperatures, we use coherent population trapping and stimulated Raman techniques to realize initialization, readout, and unitary manipulation of a single spin. Each of these techniques can be performed directly along any arbitrarily chosen quantum basis, removing the need for extra control steps to map the spin to and from a preferred basis. Combining these protocols, we perform measurements of the NV center's spin coherence, a demonstration of this full optical control. Consisting solely of optical pulses, these techniques enable control within a smaller footprint and within photonic networks. Likewise, this unified approach obviates the need for both electron spin resonance manipulation and spin addressability through the intersystem crossing. This method could therefore be applied to a wide range of potential solid-state qubits, including those which currently lack a means to be addressed.
Statistical reconstruction algorithms for continuous wave electron spin resonance imaging
Kissos, Imry; Levit, Michael; Feuer, Arie; Blank, Aharon
2013-06-01
Electron spin resonance imaging (ESRI) is an important branch of ESR that deals with heterogeneous samples ranging from semiconductor materials to small live animals and even humans. ESRI can produce either spatial images (providing information about the spatially dependent radical concentration) or spectral-spatial images, where an extra dimension is added to describe the absorption spectrum of the sample (which can also be spatially dependent). The mapping of oxygen in biological samples, often referred to as oximetry, is a prime example of an ESRI application. ESRI suffers frequently from a low signal-to-noise ratio (SNR), which results in long acquisition times and poor image quality. A broader use of ESRI is hampered by this slow acquisition, which can also be an obstacle for many biological applications where conditions may change relatively quickly over time. The objective of this work is to develop an image reconstruction scheme for continuous wave (CW) ESRI that would make it possible to reduce the data acquisition time without degrading the reconstruction quality. This is achieved by adapting the so-called "statistical reconstruction" method, recently developed for other medical imaging modalities, to the specific case of CW ESRI. Our new algorithm accounts for unique ESRI aspects such as field modulation, spectral-spatial imaging, and possible limitation on the gradient magnitude (the so-called "limited angle" problem). The reconstruction method shows improved SNR and contrast recovery vs. commonly used back-projection-based methods, for a variety of simulated synthetic samples as well as in actual CW ESRI experiments.
2014-03-24
the two rf bursts for # ’ 10 (crosses) and 150 ns (circles). Gray dashed line is a best fit of a cosine to the data. PRL 100, 236802 (2008) P H Y S I C...8217 10 (crosses) and 150 ns (circles). Gray dashed line is a best fit of a cosine to the data. PRL 100, 236802 (2008) P H Y S I C A L R E V I E W L E T...T). PRL 107, 146801 (2011) P HY S I CA L R EV I EW LE T T E R S week ending 30 SEPTEMBER 2011 146801-2 (a) (b) C upon the square root of the MW power
Valley-enhanced fast relaxation of gate-controlled donor qubits in silicon
Boross, Péter; Széchenyi, Gábor; Pályi, András
2016-08-01
Gate control of donor electrons near interfaces is a generic ingredient of donor-based quantum computing. Here, we address the question: how is the phonon-assisted qubit relaxation time T 1 affected as the electron is shuttled between the donor and the interface? We focus on the example of the ‘flip-flop qubit’ (Tosi et al arXiv:1509.08538v1), defined as a combination of the nuclear and electronic states of a phosphorus donor in silicon, promising fast electrical control and long dephasing times when the electron is halfway between the donor and the interface. We theoretically describe orbital relaxation, flip-flop relaxation, and electron spin relaxation. We estimate that the flip-flop qubit relaxation time can be of the order of 100 μs, 8 orders of magnitude shorter than the value for an on-donor electron in bulk silicon, and a few orders of magnitude shorter (longer) than the predicted inhomogeneous dephasing time (gate times). All three relaxation processes are boosted by (i) the nontrivial valley structure of the electron-phonon interaction, and (ii) the different valley compositions of the involved electronic states.
Casey, Thomas M.; Fanucci, Gail E.
2016-01-01
An understanding of macromolecular conformational equilibrium in biological systems is oftentimes essential to understand function, dysfunction, and disease. For the past few years, our lab has been utilizing site-directed spin labeling (SDSL), coupled with electron paramagnetic resonance (EPR) spectroscopy, to characterize the conformational ensemble and ligand-induced conformational shifts of HIV-1 protease (HIV-1PR). The biomedical importance of characterizing the fractional occupancy of states within the conformational ensemble critically impacts our hypothesis of a conformational selection mechanism of drug-resistance evolution in HIV-1PR. The purpose of the following chapter is to give a timeline perspective of our SDSL EPR approach to characterizing conformational sampling of HIV-1PR. We provide detailed instructions for the procedure utilized in analyzing distance profiles for HIV-1PR obtained from pulsed electron–electron double resonance (PELDOR). Specifically, we employ a version of PELDOR known as double electron–electron resonance (DEER). Data are processed with the software package “DeerAnalysis” (http://www.epr.ethz.ch/software), which implements Tikhonov regularization (TKR), to generate a distance profile from electron spin-echo amplitude modulations. We assign meaning to resultant distance profiles based upon a conformational sampling model, which is described herein. The TKR distance profiles are reconstructed with a linear combination of Gaussian functions, which is then statistically analyzed. In general, DEER has proven powerful for observing structural ensembles in proteins and, more recently, nucleic acids. Our goal is to present our advances in order to aid readers in similar applications. PMID:26477251
Seo, Dong-Kyun
2007-11-14
We present a theoretical scheme for a semiquantitative analysis of electronic structures of magnetic transition metal dimer complexes within spin density functional theory (DFT). Based on the spin polarization perturbational orbital theory [D.-K. Seo, J. Chem. Phys. 125, 154105 (2006)], explicit spin-dependent expressions of the spin orbital energies and coefficients are derived, which allows to understand how spin orbitals form and change their energies and shapes when two magnetic sites are coupled either ferromagnetically or antiferromagnetically. Upon employment of the concept of magnetic orbitals in the active-electron approximation, a general mathematical formula is obtained for the magnetic coupling constant J from the analytical expression for the electronic energy difference between low-spin broken-symmetry and high-spin states. The origin of the potential exchange and kinetic exchange terms based on the one-electron picture is also elucidated. In addition, we provide a general account of the DFT analysis of the magnetic exchange interactions in compounds for which the active-electron approximation is not appropriate.
Spin injection into a two-dimensional electron gas using inter-digital-ferromagnetic contacts
Hu, C.M.; Nitta, J.; Jensen, Ane;
2002-01-01
We present a model that describes the spin injection across a single interface with two electrodes. The spin-injection rate across a typical hybrid junction made of ferromagnet (FM) and a two-dimensional electron gas (2DEG) is found at the percentage level. We perforin spin-injection-detection ex......-injection-detection experiment on devices with two ferromagnetic contacts on a 2DEG confined in an InAs quantum well. A spin-injection rate of 4.5% is estimated from the measured magnetoresistance....
Electron Spin Resonance of Tetrahedral Transition Metal Oxyanions (MO4n-) in Solids.
Greenblatt, M.
1980-01-01
Outlines general principles in observing sharp electron spin resonance (ESR) lines in the solid state by incorporating the transition metal ion of interest into an isostructural diamagnetic host material in small concentration. Examples of some recent studies are described. (CS)
Lewis, Alan M; Hore, P J
2014-01-01
We describe how the semiclassical theory of radical pair recombination reactions recently introduced by two of us [D. E. Manolopoulos and P. J. Hore, J. Chem. Phys. 139, 124106 (2013)] can be generalised to allow for different singlet and triplet recombination rates. This is a non-trivial generalisation because when the recombination rates are different the recombination process is dynamically coupled to the coherent electron spin dynamics of the radical pair. Furthermore, because the recombination operator is a two-electron operator, it is no longer sufficient simply to consider the two electrons as classical vectors: one has to consider the complete set of 16 two-electron spin operators as independent classical variables. The resulting semiclassical theory is first validated by comparison with exact quantum mechanical results for a model radical pair containing 12 nuclear spins. It is then used to shed light on the spin dynamics of a carotenoid-porphyrin-fullerene (CPF) triad containing considerably more nu...
Spintronics and chirality: spin selectivity in electron transport through chiral molecules.
Naaman, Ron; Waldeck, David H
2015-04-01
Recent experiments have demonstrated that the electron transmission yield through chiral molecules depends on the electron spin orientation. This phenomenon has been termed the chiral-induced spin selectivity (CISS) effect, and it provides a challenge to theory and promise for organic molecule-based spintronic devices. This article reviews recent developments in our understanding of CISS. Different theoretical models have been used to describe the effect; however, they all presume an unusually large spin-orbit coupling in chiral molecules for the effect to display the magnitudes seen in experiments. A simplified model for an electron's transport through a chiral potential suggests that these large couplings can be manifested. Techniques for measuring spin-selective electron transport through molecules are overviewed, and some examples of recent experiments are described. Finally, we present results obtained by studying several systems, and we describe the possible application of the CISS effect for memory devices.
Yum, Dahyun; Dutta, Tarun; Mukherjee, Manas
2016-01-01
We demonstrate an optical single qubit based on 6S1/2 to 5D5/2 quadrupole transition of a single Ba+ ion operated by diode based lasers only. The resonance wavelength of the 6S1/2 to 5D5/2 quadrupole transition is about 1762 nm which suitably falls close to the U-band of the telecommunication wavelength. Thus this qubit is a naturally attractive choice towards implementation of quantum repeater or quantum networks using existing telecommunication networks. We observe continuous bit-flip oscillations at a rate of about 250 kHz which is fast enough for the qubit operation as compared to the measured coherence time of over 3 ms. We also present a technique to quantify the bit-flip error in each qubit NOT gate operation.
Isotope sensitive measurement of the hole-nuclear spin interaction in quantum dots
Chekhovich, E. A.; Krysa, A. B.; Hopkinson, M.; Senellart, P.; Lemaitre, A.; Skolnick, M. S.; Tartakovskii, A. I.
2011-01-01
Decoherence caused by nuclear field fluctuations is a fundamental obstacle to the realization of quantum information processing using single electron spins. Alternative proposals have been made to use spin qubits based on valence band holes having weaker hyperfine coupling. However, it was demonstrated recently both theoretically and experimentally that the hole hyperfine interaction is not negligible, although a consistent picture of the mechanism controlling the magnitude of the hole-nuclea...
Popov, Alexander A.; Lukina, Ekaterina A.; Rapatskiy, Leonid; Kulik, Leonid V.
2017-03-01
Temporal shape of electron spin echo (ESE) signal of photoinduced spin-correlated radical pairs (SCRP) in composite of conductive polymer P3HT and substituted fullerene PCBM is studied in details. ESE signals of radical pairs (RP) P3HT+/PCBM- are calculated in realistic model, taking into account finite microwave pulse length. Inhomogeneous broadening of resonant lines and interradical distance distribution are included. Experimentally observed ESE time-domain shape was found to contradict predictions of conventional SCRP theory, which would be valid in the case of very fast electron transfer. Thus, instantaneous formation of singlet SCRP is not the case for P3HT+/PCBM- pair, and spin system has enough time to evolve coherently during sequential electron transfer. While it is impossible to reproduce experimental data within simple singlet SCRP model, assumption of presence of additional - with respect to what is predicted by singlet SCRP theory - AE (absorption/emission) spin polarization gives convincing accordance with the experiment. Density matrix of RP P3HT+/PCBM- is a superposition of two contributions, namely the parts reflecting (i) antiphase polarization of original singlet-born SCRP and (ii) additional AE-polarization which is generated during initial stage of charge separation. AE-polarization affects experimental ESEEM (electron spin echo envelope modulation) traces, as well as ESE shape, making impossible their interpretation via simple singlet SCRP model. However, this effect can be eliminated by averaging of ESEEM traces over EPR spectral positions. Finally, choosing the optimal gate for ESE time-domain integration and proper microwave detection phase tuning are considered.
Alkali-metal electron spin density shift induced by a helium nanodroplet
Koch, Markus; Callegari, Carlo; Ernst, Wolfgang E.
2010-01-01
Abstract Helium (He) nanodroplets provide a cold and virtually unperturbing environment for the study of weakly bound molecules and van der Waals aggregates. High resolution microwave spectroscopy and the detection of electron spin transitions in doped He droplets have recently become possible. Measurements of hyperfine-resolved electron spin resonance in potassium (39K) and rubidium (85Rb) atoms on the surface of He droplets show small line shifts relative to the bare atoms. These...
Interplay between electron spin and orbital pseudospin in double quantum dots
Park, Sooa; Yang, S. -R. Eric
2005-01-01
We investigate theoretically spin and orbital pseudospin magnetic properties of a molecular orbital in parabolic and elliptic double quantum dots (DQDs). In our many body calculation we include intra- and inter-dot electron-electron interactions, in addition to the intradot exchange interaction of `p' orbitals. We find for parabolic DQDs that, except for the half or completely filled molecular orbital, spins in different dots are ferromagnetically coupled while orbital pseudospins are antifer...
Conversion of electronic to magnonic spin current at a heavy-metal magnetic-insulator interface
Wang, Xi-guang; Li, Zhi-xiong; Zhou, Zhen-wei; Nie, Yao-zhuang; Xia, Qing-lin; Zeng, Zhong-ming; Chotorlishvili, L.; Berakdar, J.; Guo, Guang-hua
2017-01-01
Electronic spin current is convertible to magnonic spin current via the creation or annihilation of thermal magnons at the interface of a magnetic insulator and a metal with a strong spin-orbital coupling. So far this phenomenon was evidenced in the linear regime. Based on analytical and full-fledged numerical results for the nonlinear regime we demonstrate that the generated thermal magnons or magnonic spin current in the insulator is asymmetric with respect to the charge current direction in the metal and exhibits a nonlinear dependence on the charge current density, which is explained by the tuning effect of the spin Hall torque and the magnetization damping. The results are also discussed in light of, and are in line with, recent experiments pointing to a new way of nonlinear manipulation of spin with electrical means.
Optical switching of nuclear spin-spin couplings in semiconductors.
Goto, Atsushi; Ohki, Shinobu; Hashi, Kenjiro; Shimizu, Tadashi
2011-07-05
Two-qubit operation is an essential part of quantum computation. However, solid-state nuclear magnetic resonance quantum computing has not been able to fully implement this functionality, because it requires a switchable inter-qubit coupling that controls the time evolutions of entanglements. Nuclear dipolar coupling is beneficial in that it is present whenever nuclear-spin qubits are close to each other, while it complicates two-qubit operation because the qubits must remain decoupled to prevent unwanted couplings. Here we introduce optically controllable internuclear coupling in semiconductors. The coupling strength can be adjusted externally through light power and even allows on/off switching. This feature provides a simple way of switching inter-qubit couplings in semiconductor-based quantum computers. In addition, its long reach compared with nuclear dipolar couplings allows a variety of options for arranging qubits, as they need not be next to each other to secure couplings.
Temperature Dependence of Electron Spin Relaxation of 2,2-diphenyl-1-picrylhydrazyl in Polystyrene
Meyer, Virginia; Eaton, Sandra S.; Eaton, Gareth R.
2012-01-01
The electron spin relaxation rates for the stable radical DPPH (2,2-diphenyl-1-picrylhydrazyl) doped into polystyrene were studied by inversion recovery and electron spin echo at X-band and Q-band between 20 and 295 K. At low concentration (340 μM, 0.01%) spin-lattice relaxation was dominated by the Raman process and a local mode. At high concentration (140 mM, 5%) relaxation is orders of magnitude faster than at the lower concentration, and 1/T1 is approximately linearly dependent on temperature. Spin lattice relaxation rates are similar at X-band and Q-band. The temperature dependence of spin echo dephasing was faster at about 140 K than at higher or lower temperatures, which is attributed to a wagging motion of the phenyl groups. PMID:23565040
Unified dynamics of electrons and photons via Zitterbewegung and spin-orbit interaction
Leary, C. C.; Smith, Karl H.
2014-02-01
We show that when an electron or photon propagates in a cylindrically symmetric waveguide, it experiences both a Zitterbewegung effect and a spin-orbit interaction leading to identical propagation dynamics for both particles. Applying a unified perturbative approach to both particles simultaneously, we find that to first order in perturbation theory, their Hamiltonians each contain identical Darwin (Zitterbewegung) and spin-orbit terms, resulting in the unification of their dynamics. The presence of the Zitterbewegung effect may be interpreted physically as the delocalization of the electron on the scale of its Compton wavelength, or the delocalization of the photon on the scale of its wavelength in the waveguide. The presence of the spin-orbit interaction leads to the prediction of several rotational effects: the spatial or time evolution of either particle's spin or polarization vector is controlled by the sign of its orbital angular momentum quantum number or, conversely, its spatial wave function is controlled by its spin angular momentum.
Wang, Zefang; Zhao, Liang; Mak, Kin Fai; Shan, Jie
2017-02-01
We study the electronic band structure in the K/K' valleys of the Brillouin zone of monolayer WSe2 and MoSe2 by optical reflection and photoluminescence spectroscopy on dual-gated field-effect devices. Our experiment reveals the distinct spin polarization in the conduction bands of these compounds by a systematic study of the doping dependence of the A and B excitonic resonances. Electrons in the highest-energy valence band and the lowest-energy conduction band have antiparallel spins in monolayer WSe2, and parallel spins in monolayer MoSe2. The spin splitting is determined to be hundreds of meV for the valence bands and tens of meV for the conduction bands, which are in good agreement with first principles calculations. These values also suggest that both n- and p-type WSe2 and MoSe2 can be relevant for spin- and valley-based applications
Spin-Selective Electron Quantum Transport in Nonmagnetic MgZnO/ZnO Heterostructures.
Maryenko, D; Falson, J; Bahramy, M S; Dmitriev, I A; Kozuka, Y; Tsukazaki, A; Kawasaki, M
2015-11-06
We report magnetotransport measurements on a high-mobility two-dimensional electron system at the nonmagnetic MgZnO/ZnO heterointerface showing distinct behavior for electrons with spin-up and spin-down orientations. The low-field Shubnikov-de Haas oscillations manifest alternating resistance peak heights which can be attributed to distinct scattering rates for different spin orientations. The tilt-field measurements at a half-integer filling factor reveal that the majority spins show usual diffusive behavior, i.e., peaks with the magnitude proportional to the index of the Landau level at the Fermi energy. By contrast, the minority spins develop "plateaus" with the magnitude of dissipative resistivity that is fairly independent of the Landau level index and is of the order of the zero-field resistivity.
Time-dependent tunneling of spin-polarized electrons in coupled quantum wells
Cruz, H; Luis, D [Departamento de Fisica Basica, Universidad de La Laguna, 38204 La Laguna, Tenerife (Spain)], E-mail: hcruz@ull.es
2008-02-15
We have solved the in-plane momentum-dependent effective-mass nonlinear Schroedinger equation for a spin-polarized electron wave packet in a InAs double quantum well system with an interlayer voltage. Considering a time-dependent Hartree potential, we have calculated the spin-polarized nonlinear electron dynamics between both quantum wells at different in-plane momentum values and applied bias. The spin-splitting caused by the Rashba effect is combined with the level matching between the spin dependent resonant tunneling levels making possible the observed local spin density oscillations which depend on the applied bias value. The filtering efficiency has been studied using time-dependent calculations.
Coupling nitrogen-vacancy centers in diamond to superconducting flux qubits
Marcos, D.; Wubs, Martijn; Taylor, J.M.;
2010-01-01
We propose a method to achieve coherent coupling between nitrogen-vacancy (NV) centers in diamond and superconducting (SC) flux qubits. The resulting coupling can be used to create a coherent interaction between the spin states of distant NV centers mediated by the flux qubit. Furthermore, the ma...
Evolution of Spin and Charge in a System with Interacting Impurity and Conducting Electrons
张永梅; 熊诗杰
2003-01-01
We investigate the dynamics of spin and charge in an interacting system consisting of impurity and conducting electrons.The time evolution of spin and charge in the impurity is given by solving the time-dependent Schrodinger equations for the many-body states of the interacting system.By switching on the interaction between impurity and conducting electrons,the spin and charge of the impurity begin oscillations with frequencies that reflect the elementary excitations of the interacting system.The dynamics reflects the basic picture of the Kondo effect.
Direct observation of spin-resolved full and empty electron states in ferromagnetic surfaces
Berti, G., E-mail: giulia.berti@polimi.it; Calloni, A.; Brambilla, A.; Bussetti, G.; Duò, L.; Ciccacci, F. [Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo da Vinci 32, I-20133, Milano (Italy)
2014-07-15
We present a versatile apparatus for the study of ferromagnetic surfaces, which combines spin-polarized photoemission and inverse photoemission spectroscopies. Samples can be grown by molecular beam epitaxy and analyzed in situ. Spin-resolved photoemission spectroscopy analysis is done with a hemispherical electron analyzer coupled to a 25 kV-Mott detector. Inverse photoemission spectroscopy experiments are performed with GaAs crystals as spin-polarized electron sources and a UV bandpass photon detector. As an example, measurements on the oxygen passivated Fe(100)-p(1×1)O surface are presented.
Optical detection and ionization of donors in specific electronic and nuclear spin States.
Yang, A; Steger, M; Karaiskaj, D; Thewalt, M L W; Cardona, M; Itoh, K M; Riemann, H; Abrosimov, N V; Churbanov, M F; Gusev, A V; Bulanov, A D; Kaliteevskii, A K; Godisov, O N; Becker, P; Pohl, H-J; Ager, J W; Haller, E E
2006-12-01
We resolve the remarkably sharp bound exciton transitions of highly enriched 28Si using a single-frequency laser and photoluminescence excitation spectroscopy, as well as photocurrent spectroscopy. Well-resolved doublets in the spectrum of the 31P donor reflect the hyperfine coupling of the electronic and nuclear donor spins. The optical detection of the nuclear spin state, and selective pumping and ionization of donors in specific electronic and nuclear spin states, suggests a number of new possibilities which could be useful for the realization of silicon-based quantum computers.
Gate-voltage control of spin interactions between electrons and nuclei in a semiconductor
Smet, J. H.; Deutschmann, R. A.; Ertl, F.; Wegscheider, W.; Abstreiter, G.; von Klitzing, K.
2003-01-01
Semiconductors are ubiquitous in device electronics, because their charge distributions can be conveniently manipulated with applied voltages to perform logic operations. Achieving a similar level of control over the spin degrees of freedom, either from electrons or nuclei, could provide intriguing prospects for information processing and fundamental solid-state physics issues. Here, we report procedures that carry out the controlled transfer of spin angular momentum between electrons-confined to two dimensions and subjected to a perpendicular magnetic field-and the nuclei of the host semiconductor, using gate voltages only. We show that the spin transfer rate can be enhanced near a ferromagnetic ground state of the electron system, and that the induced nuclear spin polarization can be subsequently stored and ‘read-out’. These techniques can also be combined into a spectroscopic tool to detect the low-energy collective excitations in the electron system that promote the spin transfer. The existence of such excitations is contingent on appropriate electron-electron correlations, and these can be tuned by changing, for example, the electron density via a gate voltage.
Concept of a multichannel spin-resolving electron analyzer based on Mott scattering
Strocov, Vladimir N.; Petrov, Vladimir N.; Dil, J. Hugo
2015-01-01
The concept of a multichannel electron spin detector based on optical imaging principles and Mott scattering (iMott) is presented. A multichannel electron image produced by a standard angle-resolving (photo) electron analyzer or microscope is re-imaged by an electrostatic lens at an accelerating voltage of 40 kV onto the Au target. Quasi-elastic electrons bearing spin asymmetry of the Mott scattering are imaged by magnetic lenses onto position-sensitive electron CCDs whose differential signals yield the multichannel spin asymmetry image. Fundamental advantages of this concept include acceptance of inherently divergent electron sources from the electron analyzer or microscope focal plane as well as small aberrations achieved by virtue of high accelerating voltages, as demonstrated by extensive ray-tracing analysis. The efficiency gain compared with the single-channel Mott detector can be a factor of more than 104 which opens new prospects of spin-resolved spectroscopies in application not only to standard bulk and surface systems (Rashba effect, topological insulators, etc.) but also to buried heterostructures. The simultaneous spin detection combined with fast CCD readout enables efficient use of the iMott detectors at X-ray free-electron laser facilities. PMID:25931087
Geometric multiaxial representation of N -qubit mixed symmetric separable states
SP, Suma; Sirsi, Swarnamala; Hegde, Subramanya; Bharath, Karthik
2017-08-01
The study of N -qubit mixed symmetric separable states is a longstanding challenging problem as no unique separability criterion exists. In this regard, we take up the N -qubit mixed symmetric separable states for a detailed study as these states are of experimental importance and offer an elegant mathematical analysis since the dimension of the Hilbert space is reduced from 2N to N +1 . Since there exists a one-to-one correspondence between the spin-j system and an N -qubit symmetric state, we employ Fano statistical tensor parameters for the parametrization of the spin-density matrix. Further, we use a geometric multiaxial representation (MAR) of the density matrix to characterize the mixed symmetric separable states. Since the separability problem is NP-hard, we choose to study it in the continuum limit where mixed symmetric separable states are characterized by the P -distribution function λ (θ ,ϕ ) . We show that the N -qubit mixed symmetric separable states can be visualized as a uniaxial system if the distribution function is independent of θ and ϕ . We further choose a distribution function to be the most general positive function on a sphere and observe that the statistical tensor parameters characterizing the N -qubit symmetric system are the expansion coefficients of the distribution function. As an example for the discrete case, we investigate the MAR of a uniformly weighted two-qubit mixed symmetric separable state. We also observe that there exists a correspondence between the separability and classicality of states.
Measurement of electron spin transport in graphene on 6H-silicon carbide(0001)
Abel, Joseph
The focus of this thesis is to demonstrate the potential of wafer scale graphene spintronics. Graphene is a single atomic layer of sp 2-bonded carbon atoms that has high carrier mobilities, making it a desirable material for future nanoscale electronic devices. The vision of spintronics is to utilize the spin of the electron to produce novel high-speed low power consuming devices. Materials with long spin relaxation times and spin diffusion lengths are needed to realize these goals. Graphene is an ideal material as it meets these requirements and is amenable to planar device geometries. In this thesis, spin transport in wafer scale epitaxial graphene grown on the silicon face of silicon carbide is demonstrated. Non-local Hanle spin precession measurement devices were fabricated using graphene with and without a hafnium oxide interface layer between the ferromagnetic metal and graphene. The structural properties of the devices were investigated with Raman spectroscopy, x-ray photoelectric spectroscopy, Rutherford backscattering spectroscopy, scanning electron microscopy, atomic force microscopy, and transmission electron microscopy. The electrical properties of the graphene were measured utilizing Hall transport measurements. The magnetic properties of the contacts were investigated with vibrating sample magnetometery. The processes developed to fabricate the Hanle measurement devices are presented as well. A custom Hanle measurement setup was developed and utilized for the Hanle spin precession measurements. Spin precession is observed in the epitaxial graphene on silicon carbide, with improved spin transport properties with the utilization of a hafnium oxide barrier between the ferromagnetic contacts and graphene. The charge transport and spin transport properties are compared to determine the relevant spin relaxation mechanism in the devices. These results demonstrate that graphene has great potential for wafer scale production of future spintronic devices.
Wei, Hai-Rui; Deng, Fu-Guo
2013-07-29
We investigate the possibility of achieving scalable photonic quantum computing by the giant optical circular birefringence induced by a quantum-dot spin in a double-sided optical microcavity as a result of cavity quantum electrodynamics. We construct a deterministic controlled-not gate on two photonic qubits by two single-photon input-output processes and the readout on an electron-medium spin confined in an optical resonant microcavity. This idea could be applied to multi-qubit gates on photonic qubits and we give the quantum circuit for a three-photon Toffoli gate. High fidelities and high efficiencies could be achieved when the side leakage to the cavity loss rate is low. It is worth pointing out that our devices work in both the strong and the weak coupling regimes.
Two Dimensional Spin-Polarized Electron Gas at the Oxide Interfaces
Nanda, B. R. K.; Satpathy, S.
2008-01-01
The formation of a novel spin-polarized 2D electron gas at the LaMnO$_3$ monolayer embedded in SrMnO$_3$ is predicted from the first-principles density-functional calculations. The La (d) electrons become confined in the direction normal to the interface in the potential well of the La layer, serving as a positively-charged layer of electron donors. These electrons mediate a ferromagnetic alignment of the Mn t$_{2g}$ spins near the interface via the Anderson-Hasegawa double exchange and becom...
Statistical exchange-coupling errors and the practicality of scalable silicon donor qubits
Song, Yang; Das Sarma, S.
2016-12-01
Recent experimental efforts have led to considerable interest in donor-based localized electron spins in Si as viable qubits for a scalable silicon quantum computer. With the use of isotopically purified 28Si and the realization of extremely long spin coherence time in single-donor electrons, the recent experimental focus is on two-coupled donors with the eventual goal of a scaled-up quantum circuit. Motivated by this development, we simulate the statistical distribution of the exchange coupling J between a pair of donors under realistic donor placement straggles, and quantify the errors relative to the intended J value. With J values in a broad range of donor-pair separation ( 5 quantum computer.
Environmental noise spectroscopy with qubits subjected to dynamical decoupling
Szańkowski, P.; Ramon, G.; Krzywda, J.; Kwiatkowski, D.; Cywiński, Ł.
2017-08-01
A qubit subjected to pure dephasing due to classical Gaussian noise can be turned into a spectrometer of this noise by utilizing its readout under properly chosen dynamical decoupling (DD) sequences to reconstruct the power spectral density of the noise. We review the theory behind this DD-based noise spectroscopy technique, paying special attention to issues that arise when the environmental noise is non-Gaussian and/or it has truly quantum properties. While we focus on the theoretical basis of the method, we connect the discussed concepts with specific experiments, and provide an overview of environmental noise models relevant for solid-state based qubits, including quantum-dot based spin qubits, superconducting qubits, and NV centers in diamond.
Alkali-metal electron spin density shift induced by a helium nanodroplet
Koch, Markus; Callegari, Carlo; Ernst, Wolfgang E.
2010-04-01
Helium (He) nanodroplets provide a cold and virtually unperturbing environment for the study of weakly bound molecules and van der Waals aggregates. High resolution microwave spectroscopy and the detection of electron spin transitions in doped He droplets have recently become possible. Measurements of hyperfine-resolved electron spin resonance in potassium (39K) and rubidium (85Rb) atoms on the surface of He droplets show small line shifts relative to the bare atoms. These shifts were recorded for all 2I + 1 components (I is the nuclear spin) of a transition at high accuracy for He droplets ranging in size from 1000 to 15,000 He atoms. Evaluation of the spectra yields the influence of the He environment on the electron spin density at the alkali-metal nucleus. A semi-empirical model is presented that shows good qualitative agreement with the measured droplet size dependent increase of Fermi contact interaction at the nuclei of dopant K and Rb.
Quantum simulation of a spin polarization device in an electron microscope
Grillo, Vincenzo; Marrucci, Lorenzo; Karimi, Ebrahim; Zanella, Riccardo; Santamato, Enrico
2013-09-01
A proposal for an electron-beam device that can act as an efficient spin-polarization filter has been recently put forward (Karimi et al 2012 Phys. Rev. Lett. 108 044801). It is based on combining the recently developed diffraction technology for imposing orbital angular momentum to the beam with a multipolar Wien filter inducing a sort of artificial non-relativistic spin-orbit coupling. Here we reconsider the proposed device with a fully quantum-mechanical simulation of the electron-beam propagation, based on the well-established multi-slice method, supplemented with a Pauli term for taking into account the spin degree of freedom. Using this upgraded numerical tool, we study the feasibility and practical limitations of the proposed method for spin polarizing a free electron beam.
Coherent manipulation of single electron spins with Landau-Zener sweeps
Rančić, Marko J.; Stepanenko, Dimitrije
2016-12-01
We propose a method to manipulate the state of a single electron spin in a semiconductor quantum dot (QD). The manipulation is achieved by tunnel coupling a QD, labeled L , and occupied with an electron to an adjacent QD, labeled R , which is not occupied by an electron but having an energy linearly varying in time. We identify a parameter regime in which a complete population transfer between the spin eigenstates |L ↑> and |L ↓> is achieved without occupying the adjacent QD. This method is convenient due to the fact that manipulation can be done electrically, without precise knowledge of the spin resonance condition, and is robust against Zeeman level broadening caused by nuclear spins.
Momentum and Doping Dependence of Spin Excitations in Electron-Doped Cuprate Superconductors
Jing, Pengfei; Zhao, Huaisong; Kuang, Lülin; Lan, Yu; Feng, Shiping
2017-01-01
Superconductivity in copper oxides emerges on doping holes or electrons into their Mott-insulating parent compounds. The spin excitations are thought to be the mediating glue for the pairing in superconductivity. Here the momentum and doping dependence of the dynamical spin response in the electron-doped cuprate superconductors is studied based on the kinetic-energy-driven superconducting mechanism. It is shown that the dispersion of the low-energy spin excitations changes strongly upon electron doping; however, the hour-glass-shaped dispersion of the low-energy spin excitations appeared in the hole-doped case is absent on the electron-doped side due to the electron-hole asymmetry. In particular, the commensurate resonance appears in the superconducting state with the resonance energy that correlates with the dome-shaped doping dependence of the superconducting gap. Moreover, the spectral weight and dispersion of the high-energy spin excitations in the superconducting state are comparable with those in the corresponding normal state, indicating that the high-energy spin excitations do not play an important part in the pair formation.
Belykh, V. V.; Evers, E.; Yakovlev, D. R.; Fobbe, F.; Greilich, A.; Bayer, M.
2016-12-01
We develop an extended pump-probe Faraday rotation technique to study submicrosecond electron spin dynamics with picosecond time resolution in a wide range of magnetic fields. The electron spin dephasing time T2* and the longitudinal spin relaxation time T1, both approaching 250 ns in weak fields, are measured thereby in n -type bulk GaAs. By tailoring the pump pulse train through increasing the contained number of pulses, the buildup of resonant spin amplification is demonstrated for the electron spin polarization. The spin precession amplitude in high magnetic fields applied in the Voigt geometry shows a nonmonotonic dynamics deviating strongly from a monoexponential decay and revealing slow beatings. The beatings indicate a two spin component behavior with a g -factor difference of Δ g ˜4 ×10-4 , much smaller than the Δ g expected for free and donor-bound electrons. This g -factor variation indicates efficient, but incomplete spin exchange averaging.
3D optical manipulation of a single electron spin
Geiselmann, Michael; Renger, Jan; Say, Jana M; Brown, Louise J; de Abajo, F Javier García; Koppens, Frank; Quidant, Romain
2013-01-01
Nitrogen vacancy (NV) centers in diamond are promising elemental blocks for quantum optics [1, 2], spin-based quantum information processing [3, 4], and high-resolution sensing [5-13]. Yet, fully exploiting these capabilities of single NV centers requires strategies to accurately manipulate them. Here, we use optical tweezers as a tool to achieve deterministic trapping and 3D spatial manipulation of individual nano-diamonds hosting a single NV spin. Remarkably, we find the NV axis is nearly fixed inside the trap and can be controlled in-situ, by adjusting the polarization of the trapping light. By combining this unique spatial and angular control with coherent manipulation of the NV spin and fluorescent lifetime measurements near an integrated photonic system, we prove optically trapped NV center as a novel route for both 3D vectorial magnetometry and sensing of the local density of optical states.
Coupling nitrogen-vacancy centers in diamond to superconducting flux qubits.
Marcos, D; Wubs, M; Taylor, J M; Aguado, R; Lukin, M D; Sørensen, A S
2010-11-19
We propose a method to achieve coherent coupling between nitrogen-vacancy (NV) centers in diamond and superconducting (SC) flux qubits. The resulting coupling can be used to create a coherent interaction between the spin states of distant NV centers mediated by the flux qubit. Furthermore, the magnetic coupling can be used to achieve a coherent transfer of quantum information between the flux qubit and an ensemble of NV centers. This enables a long-term memory for a SC quantum processor and possibly an interface between SC qubits and light.
Coupling nitrogen-vacancy centers in diamond to superconducting flux qubits
Marcos, D.; Wubs, Martijn; Taylor, J.M.
2010-01-01
We propose a method to achieve coherent coupling between nitrogen-vacancy (NV) centers in diamond and superconducting (SC) flux qubits. The resulting coupling can be used to create a coherent interaction between the spin states of distant NV centers mediated by the flux qubit. Furthermore, the ma......, the magnetic coupling can be used to achieve a coherent transfer of quantum information between the flux qubit and an ensemble of NV centers. This enables a long-term memory for a SC quantum processor and possibly an interface between SC qubits and light....
Coherent Zeeman resonance from electron spin coherence in a mixed-type GaAs/AlAs quantum well.
O'Leary, Shannon; Wang, Hailin; Prineas, John P
2007-03-01
Coherent Zeeman resonance from electron spin coherence is demonstrated in a Lambda-type three-level system, coupling electron spin states via trions. The optical control of electron density that is characteristic of a mixed-type quantum-well facilitates the study of trion formation as well as the effects of many-body interactions on the manifestation of electron spin coherence in the nonlinear optical response.
Dineykhan, M; Zhaugasheva, S A; Al Farabi Kazakh State National University. Almaty
2005-01-01
Multilayer nanocrystalline structure is represented by the electrostatic field inducted by total image charge, and the confinement potential for electrons is determined. Assuming that at a given distance the confinement potential is equal to the Coulomb repulsion and an interaction between electrons becomes spin-orbit, the constant of the spin-orbit interaction of electrons in nanostructures is determined. The dependence of the constant of the spin-orbit interaction on environment parameters and the distance between electrons is studied.
Hoi, Bui Dinh; Yarmohammadi, Mohsen; Kazzaz, Houshang Araghi
2017-10-01
We studied how the strain, induced exchange field and extrinsic Rashba spin-orbit coupling (RSOC) enhance the electronic band structure (EBS) and electronic heat capacity (EHC) of ferromagnetic silicene in presence of external electric field (EF) by using the Kane-Mele Hamiltonian, Dirac cone approximation and the Green's function approach. Particular attention is paid to investigate the EHC of spin-up and spin-down bands at Dirac K and K‧ points. We have varied the EF, strain, exchange field and RSOC to tune the energy of inter-band transitions and consequently EHC, leading to very promising features for future applications. Evaluation of EF exhibits three phases: Topological insulator (TI), valley-spin polarized metal (VSPM) and band insulator (BI) at given aforementioned parameters. As a new finding, we have found a quantum anomalous Hall phase in BI regime at strong RSOCs. Interestingly, the effective mass of carriers changes with strain, resulting in EHC behaviors. Here, exchange field has the same behavior with EF. Finally, we have confirmed the reported and expected symmetry results for both Dirac points and spins with the study of valley-dependent EHC.
Coupling a Surface Acoustic Wave to an Electron Spin in Diamond via a Dark State
D. Andrew Golter
2016-12-01
Full Text Available The emerging field of quantum acoustics explores interactions between acoustic waves and artificial atoms and their applications in quantum information processing. In this experimental study, we demonstrate the coupling between a surface acoustic wave (SAW and an electron spin in diamond by taking advantage of the strong strain coupling of the excited states of a nitrogen vacancy center while avoiding the short lifetime of these states. The SAW-spin coupling takes place through a Λ-type three-level system where two ground spin states couple to a common excited state through a phonon-assisted as well as a direct dipole optical transition. Both coherent population trapping and optically driven spin transitions have been realized. The coherent population trapping demonstrates the coupling between a SAW and an electron spin coherence through a dark state. The optically driven spin transitions, which resemble the sideband transitions in a trapped-ion system, can enable the quantum control of both spin and mechanical degrees of freedom and potentially a trapped-ion-like solid-state system for applications in quantum computing. These results establish an experimental platform for spin-based quantum acoustics, bridging the gap between spintronics and quantum acoustics.
Controllable entanglement sudden birth of Heisenberg spins
ZHENG Qiang; ZHI Qi-Jun; ZHANG Xiao-ping; REN Zhong-Zhou
2011-01-01
We investigate the Entanglement Sudden Birth (ESB) of two Heisenberg spins A and B. The third controller, qutrit C is introduced, which only has the Dzyaloshinskii-Moriya (DM) spin-orbit interaction with qubit B. We find that the DM interaction is necessary to induce the Entanglement Sudden Birth of the system qubits A and B, and the initial states of the system qubits and the qurit C are also important to control its Entanglement Sudden Birth.
Electron spin relaxation due to reorientation of a permanent zero field splitting tensor.
Schaefle, Nathaniel; Sharp, Robert
2004-09-15
Electron spin relaxation of transition metal ions with spin S> or =1 results primarily from thermal modulation of the zero field splitting (zfs) tensor. This occurs both by distortion of the zfs tensor due to intermolecular collisions and, for complexes with less than cubic symmetry, by reorientational modulation of the permanent zfs tensor. The reorientational mechanism is much less well characterized in previous work than the distortional mechanism although it is an important determinant of nuclear magnetic resonance (NMR) paramagnetic relaxation enhancement phenomena (i.e., the enhancement of NMR relaxation rates produced by paramagnetic ions in solution or NMR-PRE). The classical density matrix theory of spin relaxation does not provide an appropriate description of the reorientational mechanism at low Zeeman field strengths because the zero-order spin wave functions are stochastic functions of time. Using spin dynamics simulation techniques, the time correlation functions of the spin operators have been computed and used to determine decay times for the reorientational relaxation mechanism for S=1. In the zfs limit of laboratory field strengths (H(Zeem)spin decay is exponential, the spin relaxation time, tau(S) (composite function) approximately 0.53tau(R)((1)), where tau(R)((1)) is the reorientational correlation time of a molecule-fixed vector. The value of tau(S) (composite function) is independent of the magnitude of the cylindrical zfs parameter (D), but it depends strongly on low symmetry zfs terms (the E/D ratio). Other spin dynamics (SD) simulations examined spin decay in the intermediate regime of field strengths where H(Zeem) approximately H(zfs) (composite function), and in the vicinity of the Zeeman limit. The results demonstrate that the reorientational electron spin relaxation mechanism is often significant when H(zfs) (composite function)> or =H(Zeem), and that its neglect can lead to serious errors in the interpretation of NMR-PRE data.
Lagrangian for Frenkel electron and position's non-commutativity due to spin
Deriglazov, Alexei A. [Universidade Federal de Juiz de Fora, Depto. de Matematica, ICE, Juiz de Fora, MG (Brazil); Tomsk Polytechnic University, Laboratory of Mathematical Physics, Tomsk (Russian Federation); Pupasov-Maksimov, Andrey M. [Universidade Federal de Juiz de Fora, Depto. de Matematica, ICE, Juiz de Fora, MG (Brazil)
2014-10-15
We construct a relativistic spinning-particle Lagrangian where spin is considered as a composite quantity constructed on the base of a non-Grassmann vector-like variable. The variational problem guarantees both a fixed value of the spin and the Frenkel condition on the spin-tensor. The Frenkel condition inevitably leads to relativistic corrections of the Poisson algebra of the position variables: their classical brackets became noncommutative. We construct the relativistic quantum mechanics in the canonical formalism (in the physical-time parametrization) and in the covariant formalism (in an arbitrary parametrization). We show how state vectors and operators of the covariant formulation can be used to compute the mean values of physical operators in the canonical formalism, thus proving its relativistic covariance. We establish relations between the Frenkel electron and positive-energy sector of the Dirac equation. Various candidates for the position and spin operators of an electron acquire clear meaning and interpretation in the Lagrangian model of the Frenkel electron. Our results argue in favor of Pryce's (d)-type operators as the spin and position operators of Dirac theory. This implies that the effects of non-commutativity could be expected already at the Compton wavelength. We also present the manifestly covariant form of the spin and position operators of the Dirac equation. (orig.)
High-sensitivity Q-band electron spin resonance imaging system with submicron resolution
Shtirberg, Lazar; Twig, Ygal; Dikarov, Ekaterina; Halevy, Revital; Levit, Michael; Blank, Aharon
2011-04-01
A pulsed electron spin resonance (ESR) microimaging system operating at the Q-band frequency range is presented. The system includes a pulsed ESR spectrometer, gradient drivers, and a unique high-sensitivity imaging probe. The pulsed gradient drivers are capable of producing peak currents ranging from ˜9 A for short 150 ns pulses up to more than 94 A for long 1400 ns gradient pulses. Under optimal conditions, the imaging probe provides spin sensitivity of ˜1.6 × 108 spins/√Hz or ˜2.7 × 106 spins for 1 h of acquisition. This combination of high gradients and high spin sensitivity enables the acquisition of ESR images with a resolution down to ˜440 nm for a high spin concentration solid sample (˜108 spins/μm3) and ˜6.7 μm for a low spin concentration liquid sample (˜6 × 105 spins/μm3). Potential applications of this system range from the imaging of point defects in crystals and semiconductors to measurements of oxygen concentration in biological samples.
Oulton, R; Greilich, A; Verbin, S Yu; Cherbunin, R V; Auer, T; Yakovlev, D R; Bayer, M; Merkulov, I A; Stavarache, V; Reuter, D; Wieck, A D
2007-03-09
A key to ultralong electron spin memory in quantum dots (QDs) at zero magnetic field is the polarization of the nuclei, such that the electron spin is stabilized along the average nuclear magnetic field. We demonstrate that spin-polarized electrons in n-doped (In,Ga)As/GaAs QDs align the nuclear field via the hyperfine interaction. A feedback onto the electrons occurs, leading to stabilization of their polarization due to formation of a nuclear spin polaron [I. A. Merkulov, Phys. Solid State 40, 930 (1998)]. Spin depolarization of both systems is consequently greatly reduced, and spin memory of the coupled electron-nuclear spin system is retained over 0.3 sec at temperature of 2 K.
Ludwig, E.; Naggert, H.; Kallaene, Matthias; Rohlf, S.; Kröger, E.; Bannwarth, A.; Quer, A.; Rossnagel, K.; Kipp, L.; Tuczek, F
2014-01-01
The electronic structure of the iron(II) spin crossover complex [Fe(H2bpz)2(phen)] deposited as an ultrathin film on Au(111) is determined by means of UV-photoelectron spectroscopy (UPS) in the high-spin and in the low-spin state. This also allows monitoring the thermal as well as photoinduced spin transition in this system. Moreover, the complex is excited to the metastable high-spin state by irradiation with vacuum-UV light. Relaxation rates after photoexcitation are determined as a functio...
Bodek, K.; Rozpędzik, D.; Zejma, J. [Jagiellonian University, Faculty of Physics, Astronomy and Applied Informatics, Reymonta 4, 30059 Kraków (Poland); Caban, P.; Rembieliński, J.; Włodarczyk, M. [University of Łódź, Faculty of Physics and Applied Informatics, Pomorska 149/153, 90236 Łódź (Poland); Ciborowski, J. [University of Warsaw, Faculty of Physics, Hoza 69, 00681 Warsaw (Poland); Enders, J.; Köhler, A. [Technische Universität Darmstadt, Institut für Kernphysik, Schlossgartenstraße 9, 64289 Darmstadt (Germany); Kozela, A. [Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31342 Kraków (Poland)
2013-11-07
The Polish-German project QUEST aims at studying relativistic quantum spin correlations of the Einstein-Rosen-Podolsky-Bohm type, through measurement of the correlation function and the corresponding probabilities for relativistic electron pairs. The results will be compared to theoretical predictions obtained by us within the framework of relativistic quantum mechanics, based on assumptions regarding the form of the relativistic spin operator. Agreement or divergence will be interpreted in the context of non-uniqueness of the relativistic spin operator in quantum mechanics as well as dependence of the correlation function on the choice of observables representing the spin. Pairs of correlated electrons will originate from the Mo/ller scattering of polarized 15 MeV electrons provided by the superconducting Darmstadt electron linear accelerator S-DALINAC, TU Darmstadt, incident on a Be target. Spin projections will be determined using the Mott polarimetry technique. Measurements (starting 2013) are planned for longitudinal and transverse beam polarizations and different orientations of the beam polarization vector w.r.t. the Mo/ller scattering plane. This is the first project to study relativistic spin correlations for particles with mass.
Wencka, M; Lijewski, S; Hoffmann, S K [Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznan (Poland)], E-mail: mwencka@ifmpan.poznan.pl
2008-06-25
ESR spectra were recorded in the X-band (9.6 GHz) and in the W-band (94 GHz) and electron spin relaxation was measured by electron spin echo (ESE) in the temperature range 4.2-300 K for radicals in natural calcite samples obtained from a cave stalactite and a dripstone layer. Four types of carbonate radical spectra and two sulfate radical spectra were identified and high accuracy g-factors were derived. Time and temperature behaviour of the spectra show that the dominating CO{sub 2}{sup -} radicals are rigidly bonded or undergo free reorientations, whereas CO{sub 3}{sup -}, SO{sub 2}{sup -} and SO{sub 3}{sup -} only undergo free reorientations. Below 200 K the free reorientations of CO{sub 2}{sup -} are suppressed and a hindered rotation around single local axis appears. The ESE detected spectrum proves that the lines of free rotating radicals are homogeneously broadened, thus they cannot participate in electron spin echo formation. Spin-lattice relaxation data show that CO{sub 2}{sup -} radicals are decoupled from lattice phonons and relax via local mode tunnelling motion between inequivalent oxygen positions of CO{sub 2}{sup -} molecules. The tunnelling appears in two excited vibrational states of energy 71 and 138 cm{sup -1}. Librational motions of CO{sub 2}{sup -} molecules were detected by electron spin echo decay (phase relaxation) with energy 153 cm{sup -1}. Two kinds of impurity hydrogen atoms were distinguished from ESEEM: in-water inclusions and water coordinated to the calcium ions.
Repeated quantum error correction on a continuously encoded qubit by real-time feedback.
Cramer, J; Kalb, N; Rol, M A; Hensen, B; Blok, M S; Markham, M; Twitchen, D J; Hanson, R; Taminiau, T H
2016-05-05
Reliable quantum information processing in the face of errors is a major fundamental and technological challenge. Quantum error correction protects quantum states by encoding a logical quantum bit (qubit) in multiple physical qubits. To be compatible with universal fault-tolerant computations, it is essential that states remain encoded at all times and that errors are actively corrected. Here we demonstrate such active error correction on a continuously protected logical qubit using a diamond quantum processor. We encode the logical qubit in three long-lived nuclear spins, repeatedly detect phase errors by non-destructive measurements, and apply corrections by real-time feedback. The actively error-corrected qubit is robust against errors and encoded quantum superposition states are preserved beyond the natural dephasing time of the best physical qubit in the encoding. These results establish a powerful platform to investigate error correction under different types of noise and mark an important step towards fault-tolerant quantum information processing.
Repeated quantum error correction on a continuously encoded qubit by real-time feedback
Cramer, J.; Kalb, N.; Rol, M. A.; Hensen, B.; Blok, M. S.; Markham, M.; Twitchen, D. J.; Hanson, R.; Taminiau, T. H.
2016-05-01
Reliable quantum information processing in the face of errors is a major fundamental and technological challenge. Quantum error correction protects quantum states by encoding a logical quantum bit (qubit) in multiple physical qubits. To be compatible with universal fault-tolerant computations, it is essential that states remain encoded at all times and that errors are actively corrected. Here we demonstrate such active error correction on a continuously protected logical qubit using a diamond quantum processor. We encode the logical qubit in three long-lived nuclear spins, repeatedly detect phase errors by non-destructive measurements, and apply corrections by real-time feedback. The actively error-corrected qubit is robust against errors and encoded quantum superposition states are preserved beyond the natural dephasing time of the best physical qubit in the encoding. These results establish a powerful platform to investigate error correction under different types of noise and mark an important step towards fault-tolerant quantum information processing.
Note: High sensitivity pulsed electron spin resonance spectroscopy with induction detection.
Twig, Ygal; Dikarov, Ekaterina; Hutchison, Wayne D; Blank, Aharon
2011-07-01
Commercial electron spin resonance spectroscopy and imaging systems make use of the so-called "induction" or "Faraday" detection, which is based on a radio frequency coil or a microwave resonator. The sensitivity of induction detection does not exceed ~3 × 10(8) spins/√Hz. Here we show that through the use of a new type of surface loop-gap microresonators (inner size of 20 μm), operating at cryogenic temperatures at a field of 0.5 T, one can improve upon this sensitivity barrier by more than 2 orders of magnitude and reach spin sensitivities of ~1.5 × 10(6) spins/√Hz or ~2.5 × 10(4) spins for 1 h.
Conduction electron spin resonance in Mg 1 - x Al x B2
Likodimos, V.; Koutandos, S.; Pissas, M.; Papavassiliou, G.; Prassides, K.
2003-01-01
Conduction electron spin resonance is employed to study the interplay of the electronic and structural properties in the normal state of Mg 1 - x Al x B2 alloys as a function of Al-doping for 0 <= x <= 1. The x-dependence of the spin susceptibility reveals considerable reduction of the total density of states N(EF) with increasing Al concentration, complying with theoretical predictions for a predominant filling effect of the hole σ bands by electron doping. The CESR linewidth exhibits significant broadening, especially prominent in the high-Al-content region, indicative of the presence of enhanced structural disorder, consistent with the presence of compositional fluctuations.
A Spin-Light Polarimeter for Multi-GeV Longitudinally Polarized Electron Beams
Mohanmurthy, Prajwal [Mississippi State University, Starkville, MS (United States); Dutta, Dipangkar [Mississippi State University, Starkville, MS (United States) and Thomas Jefferson National Accelerator Facility, Newport News, VA (United States)
2014-02-01
The physics program at the upgraded Jefferson Lab (JLab) and the physics program envisioned for the proposed electron-ion collider (EIC) include large efforts to search for interactions beyond the Standard Model (SM) using parity violation in electroweak interactions. These experiments require precision electron polarimetry with an uncertainty of < 0.5 %. The spin dependent Synchrotron radiation, called "spin-light," can be used to monitor the electron beam polarization. In this article we develop a conceptual design for a "spin-light" polarimeter that can be used at a high intensity, multi-GeV electron accelerator. We have also built a Geant4 based simulation for a prototype device and report some of the results from these simulations.
Spin dynamics in Kapitza-Dirac scattering of electrons from bichromatic laser fields
Dellweg, Matthias M; Müller, Carsten
2016-01-01
Kapitza-Dirac scattering of nonrelativistic electrons from counterpropagating bichromatic laser waves of linear polarization i s studied. The focus lies on the electronic spin dynamics in the Bragg regime when the laser fields possess a frequency ratio of two. To this end, the time-dependent Pauli equation is solved numerically, both in coordinate space and momentum space. Our numerical results are corroborated by analytical derivations. We demonstrate that, for certain incident electron momenta, the scattering crucially relies on the electron spin which undergo es characteristic Rabi-like oscillations. A parameter regime is identified where the Rabi oscillations reach maximum amplitude. We also briefly discuss spin-dependent Kapitza-Dirac scattering of protons.
Ma Lei; Huang Ai-Qun; Li Jun
2011-01-01
This paper studies the normal state properties of itinerant electrons in a toy model, which is constructed according to the model for coexisting ferromagnetism and superconductivity proposed by Suhl [Suhl H 2001 Phys. Rev. Lett. 87 167007]. In this theory with ferromagnetic ordering based on localized spins, the exchange interaction J between conduction electrons and localized spin is taken as the pairing glue for s-wave superconductivity. It shows that this J term will first renormalize the normal state single conduction electron structures substantially. It finds dramatically enhanced or suppressed magnetization of itinerant electrons for positive or negative J. Singlet Cooper pairing can be ruled out due to strong spin polarisation in the J > 0 case while a narrow window for s-wave superconductivity is opened around some ferromagnetic J.
A Spin-Light Polarimeter for Multi-GeV Longitudinally Polarized Electron Beams
Mohanmurthy, Prajwal
2014-01-01
The physics program at the upgraded Jefferson Lab (JLab) and the physics program envisioned for the proposed electron-ion collider (EIC) include large efforts to search for interactions beyond the Standard Model (SM) using parity violation in electroweak interactions. These experiments require precision electron polarimetry with an uncertainty of $<$ 0.5 %. The spin dependent Synchrotron radiation, called "spin-light," can be used to monitor the electron beam polarization. In this article we develop a conceptual design for a "spin-light" polarimeter that can be used at a high intensity, multi-GeV electron accelerator. We have also built a Geant4 based simulation for a prototype device and report some of the results from these simulations.
2D Spin-Dependent Diffraction of Electrons From Periodical Chains of Nanomagnets
Teshome Senbeta
2012-03-01
Full Text Available The scattering of the unpolarized beams of electrons by nanomagnets in the vicinity of some scattering angles leads to complete spin polarized electrons. This result is obtained with the help of the perturbation theory. The dipole-dipole interaction between the magnetic moment of the nanomagnet and the magnetic moment of electron is treated as perturbation. This interaction is not spherically symmetric. Rather it depends on the electron spin variables. It in turn results in spinor character of the scattering amplitudes. Due to the smallness of the magnetic interactions, the scattering length of this process is very small to be proved experimentally. To enhance the relevant scattering lengths, we considered the diffraction of unpolarized beams of electrons by linear chains of nanomagnets. By tuning the distance between the scatterers it is possible to obtain the diffraction maximum of the scattered electrons at scattering angles which corresponds to complete spin polarization of electrons. It is shown that the total differential scattering length is proportional to N2 (N is a number of scatterers. Even small number of nanomagnets in the chain helps to obtain experimentally visible enhancement of spin polarization of the scattered electrons.
Magnetotransport of hot electrons and holes in the spin-valve transistor
Gökcan, Hüsey
2006-01-01
The conventional electronics uses the charge property of the electrons and holes. The building blocks are semiconductors which can be tuned to change the properties of the devices. In the field of spintronics, the spin property of the charge carriers is added to the functionality of the devices. The
Towards quantum optics and entanglement with electron spin ensembles in semiconductors
van der Wal, Caspar H.; Sladkov, Maksym
2009-01-01
We discuss a technique and a material system that enable the controlled realization of quantum entanglement between spin-wave modes of electron ensembles in two spatially separated pieces of semiconductor material. The approach uses electron ensembles in GaAs quantum wells that are located inside op
Spin and charge transport in a gated two dimensional electron gas
Lerescu, Alexandru Ionut
2007-01-01
The work presented in this thesis is centered around the idea of how one can inject, transport and detect the electron's spin in a two dimensional electron gas (a semiconductor heterostructure). Metal based spintronic devices have been established to be the easy way to implement spintronic concepts
Bell, Matthew; Zhang, Wenyuan; Ioffe, Lev; Gershenson, Michael
2014-03-01
We have studied the coherent flux tunneling in a qubit containing two submicron Josephson junctions shunted by a superinductor (a dissipationless inductor with an impedance much greater than the resistance quantum). The two low energy quantum states of this device, " open="|"> 0 and " open="|"> 1, are represented by even and odd number of fluxes in the loop, respectively. This device is dual to the charge pairing Josephson rhombi qubit. The spectrum of the device, studied by microwave spectroscopy, reflects the interference between coherent quantum phase slips in the two junctions (the Aharonov-Casher effect). The time domain measurements demonstrate the suppression of the qubit's energy relaxation in the protected regime, which illustrates the potential of this flux pairing device as a protected quantum circuit. Templeton Foundation, NSF, and ARO.
Lévay, Péter
2011-01-01
We link the recently discovered black hole-qubit correspondence to the structure of extra dimensions. In particular we show that for toroidal compactifications of type IIB string theory simple qubit systems arise naturally from the geometrical data of the tori parametrized by the moduli. We also generalize the recently suggested idea of the attractor mechanism as a distillation procedure of GHZ-like entangled states on the event horizon, to moduli stabilization for flux attractors in F-theory compactifications on elliptically fibered Calabi-Yau four-folds. Finally using a simple example we show that the natural arena for qubits to show up is an embedded one within the realm of fermionic entanglement of quantum systems with indistinguishable constituents.
Coherent spin-exchange via a quantum mediator
Baart, Timothy Alexander; Fujita, Takafumi; Reichl, Christian; Wegscheider, Werner; Vandersypen, Lieven Mark Koenraad
2017-01-01
Coherent interactions at a distance provide a powerful tool for quantum simulation and computation. The most common approach to realize an effective long-distance coupling 'on-chip' is to use a quantum mediator, as has been demonstrated for superconducting qubits and trapped ions. For quantum dot arrays, which combine a high degree of tunability with extremely long coherence times, the experimental demonstration of the time evolution of coherent spin-spin coupling via an intermediary system remains an important outstanding goal. Here, we use a linear triple-quantum-dot array to demonstrate a coherent time evolution of two interacting distant spins via a quantum mediator. The two outer dots are occupied with a single electron spin each, and the spins experience a superexchange interaction through the empty middle dot, which acts as mediator. Using single-shot spin readout, we measure the coherent time evolution of the spin states on the outer dots and observe a characteristic dependence of the exchange frequency as a function of the detuning between the middle and outer dots. This approach may provide a new route for scaling up spin qubit circuits using quantum dots, and aid in the simulation of materials and molecules with non-nearest-neighbour couplings such as MnO (ref. 27), high-temperature superconductors and DNA. The same superexchange concept can also be applied in cold atom experiments.
Mitrikas, George; Sanakis, Yiannis; Raptopoulou, Catherine P; Kordas, George; Papavassiliou, Georgios
2008-02-01
Electron spins of molecular magnets are promising candidates for large scale quantum information processing because they exhibit a large number of low-lying excited states. In this paper X-band pulse electron paramagnetic resonance spectroscopy is used to determine the intrinsic relaxation times T1 and T2 of a molecular magnet with an S = 1/2 ground state, namely the neutral trinuclear oxo-centered iron (III) complex, [Fe3(micro3-O)(O2CPh)5(salox)(EtOH)(EtOH)(H2O)]. The temperature dependence of the spin-lattice relaxation time T1 between 4.5 and 11 K shows that the Orbach relaxation process is dominant with the first excited state lying 57 cm(-1) above the ground state, whereas the phase memory time T(M) is of the order of 2.6 micros and exhibits a modest temperature dependence. These results together with previous magnetic measurements give further insight into the magnetic properties of the complex. The coherent manipulation of the electron spins is also examined by means of transient nutation experiments.
Spin-state blockade in Te6+-substituted electron-doped LaCoO3
Tomiyasu, Keisuke; Koyama, Shun-Ichi; Watahiki, Masanori; Sato, Mika; Nishihara, Kazuki; Onodera, Mitsugi; Iwasa, Kazuaki; Nojima, Tsutomu; Yamasaki, Yuuichi; Nakao, Hironori; Murakami, Youichi
2015-03-01
Perovskite-type LaCoO3 (Co3+: d6) is a rare inorganic material with sensitive and characteristic responses among low, intermediate, and high spin states. For example, in insulating nonmagnetic low-spin states below about 20 K, light hole doping (Ni substitution) induces much larger magnetization than expected; over net 10μB/hole (5μB/Ni) for 1μB/hole (1μB/Ni), in which the nearly isolated dopants locally change the surrounding Co low-spin states to magnetic ones and form spin molecules with larger total spin. Further, the former is isotropic, whereas the latter exhibits characteristic anisotropy probably because of Jahn-Teller distortion. In contrast, for electron doping, relatively insensitive spin-state responses were reported, as in LaCo(Ti4+) O3, but are not clarified, and are somewhat controversial. Here, we present macroscopic measurement data of another electron-doped system LaCo(Te6+) O3 and discuss the spin-state responses. This study was financially supported by Grants-in-Aid for Young Scientists (B) (No. 22740209 and 26800174) from the MEXT of Japan.
Quantum dot spin coherence governed by a strained nuclear environment
Stockill, R.; Le Gall, C.; Matthiesen, C.; Huthmacher, L.; Clarke, E.; Hugues, M.; Atatüre, M.
2016-01-01
The interaction between a confined electron and the nuclei of an optically active quantum dot provides a uniquely rich manifestation of the central spin problem. Coherent qubit control combines with an ultrafast spin–photon interface to make these confined spins attractive candidates for quantum optical networks. Reaching the full potential of spin coherence has been hindered by the lack of knowledge of the key irreversible environment dynamics. Through all-optical Hahn echo decoupling we now recover the intrinsic coherence time set by the interaction with the inhomogeneously strained nuclear bath. The high-frequency nuclear dynamics are directly imprinted on the electron spin coherence, resulting in a dramatic jump of coherence times from few tens of nanoseconds to the microsecond regime between 2 and 3 T magnetic field and an exponential decay of coherence at high fields. These results reveal spin coherence can be improved by applying large magnetic fields and reducing strain inhomogeneity. PMID:27615704
New insights into electron spin dynamics in the presence of correlated noise.
Spezia, S; Adorno, D Persano; Pizzolato, N; Spagnolo, B
2012-02-08
The changes in the spin depolarization length in zinc-blende semiconductors when an external component of correlated noise is added to a static driving electric field are analyzed for different values of field strength, noise amplitude and correlation time. Electron dynamics is simulated by a Monte Carlo procedure which takes into account all the possible scattering phenomena of the hot electrons in the medium and includes the evolution of spin polarization. Spin depolarization is studied by examining the decay of the initial spin polarization of the conduction electrons through the D'yakonov-Perel process, the only relevant relaxation mechanism in III-V crystals. Our results show that, for electric field amplitudes lower than the Gunn field, the dephasing length shortens with increasing noise intensity. Moreover, a nonmonotonic behavior of spin depolarization length with the noise correlation time is found, characterized by a maximum variation for values of noise correlation time comparable with the dephasing time. Instead, in high field conditions, we find that, critically depending on the noise correlation time, external fluctuations can positively affect the relaxation length. The influence of the inclusion of the electron-electron scattering mechanism is also shown and discussed.
Imaging spin filter for electrons based on specular reflection from iridium (001)
Kutnyakhov, D.; Lushchyk, P. [Johannes Gutenberg-Universität, Institut für Physik, 55099 Mainz (Germany); Fognini, A.; Perriard, D. [Laboratorium für Festkörperphysik, ETH Zürich, 8093 Zürich (Switzerland); Kolbe, M.; Medjanik, K.; Fedchenko, E.; Nepijko, S.A.; Elmers, H.J. [Johannes Gutenberg-Universität, Institut für Physik, 55099 Mainz (Germany); Salvatella, G.; Stieger, C.; Gort, R.; Bähler, T.; Michlmayer, T.; Acremann, Y.; Vaterlaus, A. [Laboratorium für Festkörperphysik, ETH Zürich, 8093 Zürich (Switzerland); Giebels, F.; Gollisch, H.; Feder, R. [Universität Duisburg-Essen, Theoretische Festkörperphysik, 47057 Duisburg (Germany); Tusche, C. [Max Planck-Institut für Mikrostrukturphysik, 06120 Halle (Germany); and others
2013-07-15
As Stern–Gerlach type spin filters do not work with electrons, spin analysis of electron beams is accomplished by spin-dependent scattering processes based on spin–orbit or exchange interaction. Existing polarimeters are single-channel devices characterized by an inherently low figure of merit (FoM) of typically 10{sup −4}–10{sup −3}. This single-channel approach is not compatible with parallel imaging microscopes and also not with modern electron spectrometers that acquire a certain energy and angular interval simultaneously. We present a novel type of polarimeter that can transport a full image by making use of k-parallel conservation in low-energy electron diffraction. We studied specular reflection from Ir (001) because this spin-filter crystal provides a high analyzing power combined with a “lifetime” in UHV of a full day. One good working point is centered at 39 eV scattering energy with a broad maximum of 5 eV usable width. A second one at about 10 eV shows a narrower profile but much higher FoM. A relativistic layer-KKR SPLEED calculation shows good agreement with measurements. - Highlights: • Novel type of spin polarimeter can transport a full image by making use of k{sup →}{sub ||} conservation in LEED. • When combined with a hemispherical analyzer, it acquires a certain energy and angular interval simultaneously. • Ir (001) based spin-filter provides a high analyzing power combined with a “lifetime” in UHV of a full day. • Parallel spin detection improves spin polarimeter efficiency by orders of magnitude. • A relativistic layer-KKR SPLEED calculation shows good agreement with measurements.
Schudt Christian; Schermuly Ralph T; Ghofrani Hossein A; Schütte Hartwig; Schäfer Rolf U; Tiyerili Vedat; Fuchs Beate; Kuzkaya Nermin; Weissmann Norbert; Sydykov Akylbek; Egemnazarow Bakytbek; Seeger Werner; Grimminger Friedrich
2005-01-01
Abstract Background The sources and measurement of reactive oxygen species (ROS) in intact organs are largely unresolved. This may be related to methodological problems associated with the techniques currently employed for ROS detection. Electron spin resonance (ESR) with spin trapping is a specific method for ROS detection, and may address some these technical problems. Methods We have established a protocol for the measurement of intravascular ROS release from isolated buffer-perfused and v...
Effect of Quantum Point Contact Measurement on Electron Spin State in Quantum Dots
ZHU Fei-Yun; TU Tao; HAO Xiao-Jie; GUO Guang-Can; GUO Guo-Ping
2009-01-01
We study the time evolution of two electron spin states in a double quantum-dot system, which includes a nearby quantum point contact (QPC) as a measurement device. We find that the QPC measurement induced decoherence is in the microsecond timescale. We also find that the enhanced QPC measurement will trap the system in its initial spin states, which is consistent with the quantum Zeno effect.