Exact two-qubit universal quantum circuit
Zhang, J; Sastry, S; Whaley, K B; Zhang, Jun; Vala, Jiri; Sastry, Shankar
2003-01-01
We provide an analytic way to implement any arbitrary two-qubit unitary operation, given an entangling two-qubit gate together with local gates. This is shown to provide explicit construction of a universal quantum circuit that exactly simulates arbitrary two-qubit gates. Each block in this circuit is given in a closed form solution. We also analyze the efficiency of different entangling gates, and find that exactly half of all the controlled-unitary gates can be used to implement two-qubit operations as efficiently as the commonly used CNOT gate.
On Universal Gate Libraries and Generic Minimal Two-qubit Quantum Circuits
Shende, V V; Bullock, S S; Shende, Vivek V.; Markov, Igor L.; Bullock, Stephen S.
2003-01-01
We show how to implement exactly an arbitrary two-qubit unitary operation in several universal gate libraries using the smallest possible number of gates. To this end, we prove that n-qubit circuits using CNOT and one-qubit gates require at least ceil((4^n - 3n -1)/4) CNOT gates in the worst case. For two-qubit operators, this yields a lower bound of three gates, which we match with an upper bound of three gates. Using quantum circuit identities, we improve an earlier lower bound of 17 elementary gates by Bullock and Markov to 18, and their upper bound of 23 elementary gates to 18. We also improve upon the generic circuit with six CNOT gates by Zhang et al. (our circuit uses three), and that by Vidal and Dawson with 11 basic gates (we use 10). Given the available results, it appears that some universal gate libraries are at a disadvantage, at least in the sense that no construction is known to produce smallest possible circuits.
Recognizing Small-Circuit Structure in Two-Qubit Operators
Shende, V V; Markov, I L; Shende, Vivek V.; Bullock, Stephen S.; Markov, Igor L.
2003-01-01
This work describes numerical tests which determine whether a two-qubit quantum computation has an atypically simple quantum circuit. Specifically, we describe forumulae, written in terms of matrix coefficients, characterizing operators implementable with exactly zero, one, or two controlled-not gates with all other gates being local unitary. Circuit diagrams are provided in each case. We expect significant impact in physical implementations where controlled-not's are more difficult than one-qubit computations. Our results can be contrasted with those by Zhang et al., Bullock and Markov, Vidal and Dawson, and Shende et al. In these works, small quantum circuits are achieved for arbitrary two-qubit operators, and the latter two prove three controlled-not's suffice. However, unitary operators with the sort of structure described above may not be detected. Our work provides results similar to those by Song and Klappenecker but for a wider range of operators.
Minimum construction of two-qubit quantum operations
Zhang, J; Sastry, S; Whaley, K B; Zhang, Jun; Vala, Jiri; Sastry, Shankar
2003-01-01
Optimal construction of quantum operations is a fundamental problem in the realization of quantum computation. We here introduce a newly discovered quantum gate, B, that can implement any arbitrary two-qubit quantum operation with minimal number of both two- and single-qubit gates. We show this by giving an analytic circuit that implements a generic nonlocal two-qubit operation from just two applications of the B gate. We also demonstrate that for the highly scalable Josephson junction charge qubits, the B gate is also more easily and quickly generated than the CNOT gate for physically feasible parameters.
Robust two-qubit quantum registers.
Grigorenko, I A; Khveshchenko, D V
2005-02-04
We carry out a systematic analysis of a pair of coupled qubits, each of which is subject to its own dissipative environment, and argue that a combination of the interqubit couplings which provides for the lowest possible decoherence rates corresponds to the incidence of a double spectral degeneracy in the two-qubit system. We support this general argument by the results of an evolutionary genetic algorithm which can also be used for optimizing time-dependent processes (gates) and their sequences that implement various quantum computing protocols.
Dynamical Suppression of Decoherence in Two-Qubit Quantum Memory
Institute of Scientific and Technical Information of China (English)
无
2005-01-01
In this paper, we have detailedly studied the dynamical suppression of the phase damping for the two-qubit quantum memory of Ising model by the quantum "bang-bang" technique. We find the sequence of periodic radiofrequency pulses repetitively to flip the state of the two-qubit system and quantitatively find that these pulses can be used to effectively suppress the phase damping decoherence of the quantum memory and freeze the system state into its initial state. The general sequence of periodic radio-frequency pulses to suppress the phase damping of multi-qubit of Ising model is also given.
Two-qubit quantum cloning machine and quantum correlation broadcasting
Kheirollahi, Azam; Mohammadi, Hamidreza; Akhtarshenas, Seyed Javad
2016-11-01
Due to the axioms of quantum mechanics, perfect cloning of an unknown quantum state is impossible. But since imperfect cloning is still possible, a question arises: "Is there an optimal quantum cloning machine?" Buzek and Hillery answered this question and constructed their famous B-H quantum cloning machine. The B-H machine clones the state of an arbitrary single qubit in an optimal manner and hence it is universal. Generalizing this machine for a two-qubit system is straightforward, but during this procedure, except for product states, this machine loses its universality and becomes a state-dependent cloning machine. In this paper, we propose some classes of optimal universal local quantum state cloners for a particular class of two-qubit systems, more precisely, for a class of states with known Schmidt basis. We then extend our machine to the case that the Schmidt basis of the input state is deviated from the local computational basis of the machine. We show that more local quantum coherence existing in the input state corresponds to less fidelity between the input and output states. Also we present two classes of a state-dependent local quantum copying machine. Furthermore, we investigate local broadcasting of two aspects of quantum correlations, i.e., quantum entanglement and quantum discord, defined, respectively, within the entanglement-separability paradigm and from an information-theoretic perspective. The results show that although quantum correlation is, in general, very fragile during the broadcasting procedure, quantum discord is broadcasted more robustly than quantum entanglement.
Extremal quantum correlations: Experimental study with two-qubit states
Energy Technology Data Exchange (ETDEWEB)
Chiuri, A.; Mataloni, P. [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Istituto Nazionale di Ottica (INO-CNR), L.go E. Fermi 6, I-50125 Firenze (Italy); Vallone, G. [Dipartimento di Fisica, Sapienza Universita di Roma, Piazzale Aldo Moro 5, I-00185 Roma (Italy); Museo Storico della Fisica e Centro Studi e Ricerche Enrico Fermi, Via Panisperna 89/A, Compendio del Viminale, I-00184 Roma (Italy); Paternostro, M. [Centre for Theoretical Atomic, Molecular, and Optical Physics, School of Mathematics and Physics, Queen' s University, Belfast BT7 1NN (United Kingdom)
2011-08-15
We explore experimentally the space of two-qubit quantum-correlated mixed states, including frontier states as defined by the use of quantum discord and von Neumann entropy. Our experimental setup is flexible enough to allow for high-quality generation of a vast variety of states. We address quantitatively the relation between quantum discord and a recently suggested alternative measure of quantum correlations.
Quantum discord for two-qubit X-states
Ali, Mazhar; Alber, Gernot
2010-01-01
Quantum discord, a kind of quantum correlation, is defined as the difference between quantum mutual information and classical correlation in a bipartite system. In general, this correlation is different from entanglement, and quantum discord may be nonzero even for certain separable states. Even in the simple case of bipartite quantum systems, this different kind of quantum correlation has interesting and significant applications in quantum information processing. So far, quantum discord has been calculated explicitly only for a rather limited set of two-qubit quantum states and expressions for more general quantum states are not known. In this paper, we derive explicit expressions for quantum discord for a larger class of two-qubit states, namely, a seven-parameter family of so called X-states that have been of interest in a variety of contexts in the field. We also study the relation between quantum discord, classical correlation, and entanglement for a number of two-qubit states to demonstrate that they ar...
Quantum entanglement for two qubits in a nonstationary cavity
Berman, Oleg L.; Kezerashvili, Roman Ya.; Lozovik, Yurii E.
2016-11-01
The quantum entanglement and the probability of the dynamical Lamb effect for two qubits caused by nonadiabatic fast change of the boundary conditions are studied. The conditional concurrence of the qubits for each fixed number of created photons in a nonstationary cavity is obtained as a measure of the dynamical quantum entanglement due to the dynamical Lamb effect. We discuss the physical realization of the dynamical Lamb effect, based on superconducting qubits.
Quantum entanglement for two qubits in a nonstationary cavity
Berman, Oleg L; Lozovik, Yurii E
2016-01-01
The quantum entanglement and the probability of the dynamical Lamb effect for two qubits caused by non-adiabatic fast change of the boundary conditions are studied. The conditional concurrence of the qubits for each fixed number of created photons in a nonstationary cavity is obtained as a measure of the dynamical quantum entanglement due to the dynamical Lamb effect. We discuss the physical realization of the dynamical Lamb effect, based on superconducting qubits.
Entanglement dynamics of two-qubit systems in different quantum noises
Institute of Scientific and Technical Information of China (English)
Pan Chang-Ning; Li-Fei; Fang Jian-Shu; Fang Mao-Fa
2011-01-01
The entanglement dynamics of two-qubit systems in different quantum noises are investigated by means of the operator-sum representation method. We find that, except for the amplitude damping and phase damping quantum noise, the sudden death of entanglement is always observed in different two-qubit systems with generalized amplitude damping and depolarizing quantum noise.
Demonstration of two-qubit algorithms with a superconducting quantum processor.
DiCarlo, L; Chow, J M; Gambetta, J M; Bishop, Lev S; Johnson, B R; Schuster, D I; Majer, J; Blais, A; Frunzio, L; Girvin, S M; Schoelkopf, R J
2009-07-09
Quantum computers, which harness the superposition and entanglement of physical states, could outperform their classical counterparts in solving problems with technological impact-such as factoring large numbers and searching databases. A quantum processor executes algorithms by applying a programmable sequence of gates to an initialized register of qubits, which coherently evolves into a final state containing the result of the computation. Building a quantum processor is challenging because of the need to meet simultaneously requirements that are in conflict: state preparation, long coherence times, universal gate operations and qubit readout. Processors based on a few qubits have been demonstrated using nuclear magnetic resonance, cold ion trap and optical systems, but a solid-state realization has remained an outstanding challenge. Here we demonstrate a two-qubit superconducting processor and the implementation of the Grover search and Deutsch-Jozsa quantum algorithms. We use a two-qubit interaction, tunable in strength by two orders of magnitude on nanosecond timescales, which is mediated by a cavity bus in a circuit quantum electrodynamics architecture. This interaction allows the generation of highly entangled states with concurrence up to 94 per cent. Although this processor constitutes an important step in quantum computing with integrated circuits, continuing efforts to increase qubit coherence times, gate performance and register size will be required to fulfil the promise of a scalable technology.
The two-qubit amplitude damping channel: Characterization using quantum stabilizer codes
Omkar, S.; Srikanth, R.; Banerjee, Subhashish; Shaji, Anil
2016-10-01
A protocol based on quantum error correction based characterization of quantum dynamics (QECCD) is developed for quantum process tomography on a two-qubit system interacting dissipatively with a vacuum bath. The method uses a 5-qubit quantum error correcting code that corrects arbitrary errors on the first two qubits, and also saturates the quantum Hamming bound. The dissipative interaction with a vacuum bath allows for both correlated and independent noise on the two-qubit system. We study the dependence of the degree of the correlation of the noise on evolution time and inter-qubit separation.
A two-qubit photonic quantum processor and its application to solving systems of linear equations
Stefanie Barz; Ivan Kassal; Martin Ringbauer; Yannick Ole Lipp; Borivoje Dakić; Alán Aspuru-Guzik; Philip Walther
2014-01-01
Large-scale quantum computers will require the ability to apply long sequences of entangling gates to many qubits. In a photonic architecture, where single-qubit gates can be performed easily and precisely, the application of consecutive two-qubit entangling gates has been a significant obstacle. Here, we demonstrate a two-qubit photonic quantum processor that implements two consecutive CNOT gates on the same pair of polarisation-encoded qubits. To demonstrate the flexibility of our system, w...
Scheme for Remote Implementation of Partially Unknown Quantum Operation of Two Qubits in Cavity QED
Institute of Scientific and Technical Information of China (English)
QIU Liang; WANG An-Min
2008-01-01
By constructing the recovery operations of the protocol of remote implementation of partially unknown quantum operation of two qubits [An-Min Wang: Phys. Rev. A 74 (2006) 032317] with two-qubit Cnot gate and single qubit logic gates, we present a scheme to implement it in cavity QED. Long-lived Rydberg atoms are used as qubits, and the interaction between the atoms and the field of cavity is a nonresonant one. Finally, we analyze the experimental feasibility of this scheme.
A two-qubit photonic quantum processor and its application to solving systems of linear equations.
Barz, Stefanie; Kassal, Ivan; Ringbauer, Martin; Lipp, Yannick Ole; Dakić, Borivoje; Aspuru-Guzik, Alán; Walther, Philip
2014-08-19
Large-scale quantum computers will require the ability to apply long sequences of entangling gates to many qubits. In a photonic architecture, where single-qubit gates can be performed easily and precisely, the application of consecutive two-qubit entangling gates has been a significant obstacle. Here, we demonstrate a two-qubit photonic quantum processor that implements two consecutive CNOT gates on the same pair of polarisation-encoded qubits. To demonstrate the flexibility of our system, we implement various instances of the quantum algorithm for solving of systems of linear equations.
Novotny, J; Jex, I
2006-01-01
The structure of all completely positive quantum operations is investigated which transform pure two-qubit input states of a given degree of entanglement in a covariant way. Special cases thereof are quantum NOT operations which transform entangled pure two-qubit input states of a given degree of entanglement into orthogonal states in an optimal way. Based on our general analysis all covariant optimal two-qubit quantum NOT operations are determined. In particular, it is demonstrated that only in the case of maximally entangled input states these quantum NOT operations can be performed perfectly.
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.
Two-Qubit Quantum Logic Gate in Molecular Magnets
Institute of Scientific and Technical Information of China (English)
HOU Jing-Min; TIAN Li-Jun; GE Mo-Lin
2005-01-01
@@ We propose a scheme to realize a controlled-NOT quantum logic gate in a dimer of exchange coupled singlemolecule magnets, [Mn4]2. We chosen the ground state and the three low-lying excited states of a dimer in a finite longitudinal magnetic field as the quantum computing bases and introduced a pulsed transverse magnetic field with a special frequency. The pulsed transverse magnetic field induces the transitions between the quantum computing bases so as to realize a controlled-NOT quantum logic gate. The transition rates between a pair of the four quantum computing bases and between the quantum computing bases and excited states are evaluated and analysed.
Controlled Remote Preparation of a Two-Qubit State via an Asymmetric Quantum Channel
Institute of Scientific and Technical Information of China (English)
WANG Zhang-Yin
2011-01-01
I present a new scheme for probabilistic remote preparation of a general two-qubit state from a sender to either of two receivers.The quantum channel is composed of a partial entangled tripartite Greenberger-Horne-Zeilinger (GHZ) state and a W-type state.I try to realize the remote two-qubit preparation by using the usual projective measurement and the method of positive operator-valued measure, respectively.The corresponding success probabilities of the scheme with different methods as well as the total classical communication cost required in this scheme are also calculated.
Quantum and classical correlations for a two-qubit X structure density matrix
Institute of Scientific and Technical Information of China (English)
Ding Bang-Fu; Wang Xiao-Yun; Zhao He-Ping
2011-01-01
We derive explicit expressions for quantum discord and classical correlation for an X structure density matrix.Based on the characteristics of the expressions,the quantum discord and the classical correlation are easily obtained and compared under different initial conditions using a novel analytical method.We explain the relationships among quantum discord,classical correlation,and entanglement,and further find that the quantum discord is not always larger than the entanglement measured by concurrence in a general two-qubit X state.The new method,which is different from previous approaches,has certain guiding significance for analysing quantum discord and classical correlation of a two-qubit X state,such as a mixed state.
On the quantum discord of two-qubit X-states
Chen, Qing; Yu, Sixia; Yi, X X; Oh, C H
2011-01-01
Quantum discord provides a measure for quantifying quantum correlations beyond entanglement and is very hard to compute even for two-qubit states because of the minimization over all possible measurements. Recently a simple algorithm to evaluate the quantum discord for two-qubit X-states is proposed by Ali, Rau and Alber [Phys. Rev. A 81, 042105 (2010)] with minimization taken over only a few cases. Here we shall at first identify a class of X-states, whose quantum discord can be evaluated analytically without any minimization, for which their algorithm is valid, and also identify a family of X-states for which their algorithm fails. And then we demonstrate that this special family of X-states provides furthermore an explicit example for the inequivalence between the minimization over positive operator-valued measures and that over von Neumann measurements.
Entanglement of Two-Qubit Quantum Heisenberg XYZ Chain
Institute of Scientific and Technical Information of China (English)
惠小强; 郝三如; 陈文学; 岳瑞宏
2002-01-01
We derive the analytic expression of the concurrence in the quantum Heisenberg XY Z model and discuss the influence of parameters J, △ and Γ on the concurrence. By choosing different values of Γ and △, we obtain the XX, XY, XXX and XXZ chains. The concurrence decreases with increasing temperature. When entanglement. For the XXZ chain, when Γ→∞, the concurence will meet its maximum value Cmax= sinh(1/T)--cosh(1/T)@
Application of quantum algorithms to direct measurement of concurrence of a two-qubit pure state
Institute of Scientific and Technical Information of China (English)
Wang Hong-Fu; Zhang Shou
2009-01-01
This paper proposes a method to measure directly the concurrence of an arbitrary two-qubit pure state based on a generalized Grover quantum iteration algorithm and a phase estimation algorithm. The concurrence can be calculated by applying quantum algorithms to two available copies of the bipartite system, and a final measurement on the auxiliary working qubits gives a better estimation of the concurrence. This method opens new prospects of entanglement measure by the application of quantum algorithms. The implementation of the protocol would be an important step toward quantum information processing and more complex entanglement measure of the finite-dimensional quantum system with an arbitrary number of qubits.
A practical scheme for quantum computation with any two-qubit entangling gate
Bremner, M J; Dodd, J L; Gilchrist, A; Harrow, A W; Mortimer, D; Nielsen, M A; Osborne, T J; Bremner, Michael J.; Dawson, Christopher M.; Dodd, Jennifer L.; Gilchrist, Alexei; Harrow, Aram W.; Mortimer, Duncan; Nielsen, Michael A.; Osborne, Tobias J.
2002-01-01
Which gates are universal for quantum computation? Although it is well known that certain gates on two-level quantum systems (qubits), such as the controlled-not (CNOT), are universal when assisted by arbitrary one-qubit gates, it has only recently become clear precisely what class of two-qubit gates is universal in this sense. Here we present an elementary proof that any entangling two-qubit gate is universal for quantum computation, when assisted by one-qubit gates. A proof of this important result for systems of arbitrary finite dimension has been provided by J. L. and R. Brylinski [arXiv:quant-ph/0108062, 2001]; however, their proof relies upon a long argument using advanced mathematics. In contrast, our proof provides a simple constructive procedure which is close to optimal and experimentally practical [C. M. Dawson and A. Gilchrist, online implementation of the procedure described herein (2002), http://www.physics.uq.edu.au/gqc/].
Demonstrating quantum speed-up in a superconducting two-qubit processor
Dewes, A; Ong, F R; Schmitt, V; Milman, P; Bertet, P; Vion, D; Esteve, D
2011-01-01
We operate a superconducting quantum processor consisting of two tunable transmon qubits coupled by a swapping interaction, and equipped with non destructive single-shot readout of the two qubits. With this processor, we run the Grover search algorithm among four objects and find that the correct answer is retrieved after a single run with a success probability between 0.52 and 0.67, significantly larger than the 0.25 achieved with a classical algorithm. This constitutes a proof-of-concept for the quantum speed-up of electrical quantum processors.
Conditional purity and quantum correlation measures in two qubit mixed states
Rebón, L.; Rossignoli, R.; Varga, J. J. M.; Gigena, N.; Canosa, N.; Iemmi, C.; Ledesma, S.
2016-11-01
We analyze and show experimental results of the conditional purity, the quantum discord and other related measures of quantum correlation in mixed two-qubit states constructed from a pair of photons in identical polarization states. The considered states are relevant for the description of spin pair states in interacting spin chains in a transverse magnetic field. We derive clean analytical expressions for the conditional local purity and other correlation measures obtained as a result of a remote local projective measurement, which are fully verified by the experimental results. A simple exact expression for the quantum discord of these states in terms of the maximum conditional purity is also derived.
Joint remote state preparation (JRSP) of two-qubit equatorial state in quantum noisy channels
Adepoju, Adenike Grace; Falaye, Babatunde James; Sun, Guo-Hua; Camacho-Nieto, Oscar; Dong, Shi-Hai
2017-02-01
This letter reports the influence of noisy channels on JRSP of two-qubit equatorial state. We present a protocol for JRSP of two-qubit equatorial state. Afterward, we investigate the effects of five quantum noises on the protocol. We find that the system loses some of its properties as consequence of unwanted interactions with environment. For instance, within the domain 0 < λ < 0.65, the information lost via transmission of qubits in amplitude channel is most minimal, while for 0.65 < λ ≤ 1, the information lost in phase flip channel becomes the most minimal. Also, for any given λ, the information transmitted through depolarizing channel has the least chance of success.
Speed of quantum evolution of entangled two qubits states: Local vs. global evolution
Energy Technology Data Exchange (ETDEWEB)
Curilef, S [Departamento de Fisica, Universidad Catolica del Norte, Antofagasta (Chile); Zander, C; Plastino, A R [Physics Department, University of Pretoria, Pretoria 0002 (South Africa)], E-mail: arplastino@maple.up.ac.za
2008-11-01
There is a lower bound for the 'speed' of quantum evolution as measured by the time needed to reach an orthogonal state. We show that, for two-qubits systems, states saturating the quantum speed limit tend to exhibit a small amount of local evolution, as measured by the fidelity between the initial and final single qubit states after the time {tau} required by the composite system to reach an orthogonal state. Consequently, a trade-off between the speed of global evolution and the amount of local evolution seems to be at work.
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.
Sirsi, Swarnamala; Hegde, Subramanya
2011-01-01
Quantum computation on qubits can be carried out by an operation generated by a Hamiltonian such as application of a pulse as in NMR, NQR. Quantum circuits form an integral part of quan- tum computation. We investigate the nonlocal operations generated by a given Hamiltonian. We construct and study the properties of perfect entanglers, that is, the two-qubit operations that can generate maximally entangled states from some suitably chosen initial separable states in terms of their entangling power. Our work addresses the problem of analyzing the quantum evolution in the special case of two qubit symmetric states. Such a symmetric space can be considered to be spanned by the angular momentum states {|j = 1,m>;m = +1, 0,-1}. Our technique relies on the decomposition of a Hamiltonian in terms of newly defined Hermitian operators Mk's (k= 0.....8) which are constructed out of angular momentum operators Jx, Jy, Jz. These operators constitute a linearly independent set of traceless matrices (except for M0). Further...
Indian Academy of Sciences (India)
Prasanta K Panigrahi; Siddharth Karumanchi; Sreraman Muralidharan
2009-09-01
We investigate the usefulness of the highly entangled five-partite cluster and Brown states for the quantum information splitting (QIS) of a special kind of two-qubit state using remote state preparation. In our schemes, the information that is to be shared is known to the sender. We show that, QIS can be accomplished with just two classical bits, as opposed to four classical bits, when the information that is to be shared is unknown to the sender. The present algorithm, demonstrated through the cluster and Brown states is deterministic as compared to the previous works in which it was probabilistic.
Erol, Volkan; Ozaydin, Fatih; Altintas, Azmi Ali
2014-06-24
Entanglement has been studied extensively for unveiling the mysteries of non-classical correlations between quantum systems. In the bipartite case, there are well known measures for quantifying entanglement such as concurrence, relative entropy of entanglement (REE) and negativity, which cannot be increased via local operations. It was found that for sets of non-maximally entangled states of two qubits, comparing these entanglement measures may lead to different entanglement orderings of the states. On the other hand, although it is not an entanglement measure and not monotonic under local operations, due to its ability of detecting multipartite entanglement, quantum Fisher information (QFI) has recently received an intense attraction generally with entanglement in the focus. In this work, we revisit the state ordering problem of general two qubit states. Generating a thousand random quantum states and performing an optimization based on local general rotations of each qubit, we calculate the maximal QFI for each state. We analyze the maximized QFI in comparison with concurrence, REE and negativity and obtain new state orderings. We show that there are pairs of states having equal maximized QFI but different values for concurrence, REE and negativity and vice versa.
Hassan, Ali Saif M; Joag, Pramod S
2010-01-01
We investigate how thermal quantum discord $(QD)$ and classical correlations $(CC)$ of a two qubit one-dimensional XX Heisenberg chain in thermal equilibrium depend on temperature of the bath as well as on nonuniform external magnetic fields applied to two qubits and varied separately. We show that the behaviour of $QD$ differs in many unexpected ways from thermal entanglement $(EN)$. For the nonuniform case, $(B_1= - B_2)$ we find that $QD$ and $CC$ are equal for all values of $(B_1=-B_2)$ and for different temperatures. We show that, in this case, the thermal states of the system belong to a class of mixed states and satisfy certain conditions under which $QD$ and $CC$ are equal. The specification of this class and the corresponding conditions is completely general and apply to any quantum system in a state in this class and satisfying these conditions. We further find the relative contributions of $QD$ and $CC$ can be controlled easily by changing the relative magnitudes of $B_1$ and $B_2$.
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.
Bartkiewicz, Karol; Chimczak, Grzegorz; Lemr, Karel
2017-02-01
We describe a direct method for experimental determination of the negativity of an arbitrary two-qubit state with 11 measurements performed on multiple copies of the two-qubit system. Our method is based on the experimentally accessible sequences of singlet projections performed on up to four qubit pairs. In particular, our method permits the application of the Peres-Horodecki separability criterion to an arbitrary two-qubit state. We explicitly demonstrate that measuring entanglement in terms of negativity requires three measurements more than detecting two-qubit entanglement. The reported minimal set of interferometric measurements provides a complete description of bipartite quantum entanglement in terms of two-photon interference. This set is smaller than the set of 15 measurements needed to perform a complete quantum state tomography of an arbitrary two-qubit system. Finally, we demonstrate that the set of nine Makhlin's invariants needed to express the negativity can be measured by performing 13 multicopy projections. We demonstrate both that these invariants are a useful theoretical concept for designing specialized quantum interferometers and that their direct measurement within the framework of linear optics does not require performing complete quantum state tomography.
Dorai, Kavita; Arvind; Kumar, Anil
2001-01-01
We describe the experimental implementation of a recently proposed quantum algorithm involving quantum entanglement at the level of two qubits using NMR. The algorithm solves a generalisation of the Deutsch problem and distinguishes between even and odd functions using fewer function calls than is possible classically. The manipulation of entangled states of the two qubits is essential here, unlike the Deutsch-Jozsa algorithm and the Grover's search algorithm for two bits.
Institute of Scientific and Technical Information of China (English)
Wang Qiong; Li Ji-Xin; Zeng Hao-Sheng
2009-01-01
This paper investigates the change of entanglement for transmitting an arbitrarily entangled two-qubit pure state via one of three typical kinds of noisy quantum channels:amplitude damping quantum channel,phase damping quantum channel and depolarizing quantum channel.It finds,in all these three cases,that the output distant entanglement(measured by concurrence)reduces proportionately with respect to its initial amount,and the decaying ratio is determined only by the noisy characteristics of quantum channels and independent of the form of initial input state.
Quantum Dense Coding About a Two-Qubit Heisenberg XYZ Model
Xu, Hui-Yun; Yang, Guo-Hui
2017-09-01
By taking into account the nonuniform magnetic field, the quantum dense coding with thermal entangled states of a two-qubit anisotropic Heisenberg XYZ chain are investigated in detail. We mainly show the different properties about the dense coding capacity ( χ) with the changes of different parameters. It is found that dense coding capacity χ can be enhanced by decreasing the magnetic field B, the degree of inhomogeneity b and temperature T, or increasing the coupling constant along z-axis J z . In addition, we also find χ remains the stable value as the change of the anisotropy of the XY plane Δ in a certain temperature condition. Through studying different parameters effect on χ, it presents that we can properly turn the values of B, b, J z , Δ or adjust the temperature T to obtain a valid dense coding capacity ( χ satisfies χ > 1). Moreover, the temperature plays a key role in adjusting the value of dense coding capacity χ. The valid dense coding capacity could be always obtained in the lower temperature-limit case.
Energy Technology Data Exchange (ETDEWEB)
Hassan, Ali Saif M [Department of Physics, University of Amran, Amran (Yemen); Lari, Behzad; Joag, Pramod S, E-mail: alisaif73@gmail.co, E-mail: behzadlari1979@yahoo.co, E-mail: pramod@physics.unipune.ac.i [Department of Physics, University of Pune, Pune 411007 (India)
2010-12-03
We investigate how thermal quantum discord (QD) and classical correlations (CC) of a two-qubit one-dimensional XX Heisenberg chain in thermal equilibrium depend on the temperature of the bath as well as on nonuniform external magnetic fields applied to two qubits and varied separately. We show that the behavior of QD differs in many unexpected ways from the thermal entanglement (EOF). For the nonuniform case (B{sub 1} = -B{sub 2}), we find that QD and CC are equal for all values of (B{sub 1} = -B{sub 2}) and for different temperatures. We show that, in this case, the thermal states of the system belong to a class of mixed states and satisfy certain conditions under which QD and CC are equal. The specification of this class and the corresponding conditions are completely general and apply to any quantum system in a state in this class satisfying these conditions. We further find that the relative contributions of QD and CC can be controlled easily by changing the relative magnitudes of B{sub 1} and B{sub 2}. Finally, we connect our results with the monogamy relations between the EOF, CC and the QD of two qubits and the environment.
Institute of Scientific and Technical Information of China (English)
ZHANG Han; LUO Jun; REN Ting-Ting; SUN Xian-Ping
2010-01-01
@@ We report the experimental demonstration of decoherence dynamics of entanglement for the four Bell states in two-qubit nuclear-spin systems on ensemble quantum computers.Using artificial error operators to simulate noisy channels,we experimentally investigate the effect of noises on the four Bell states,and furthermore observe the time evolution of entanglement for the four Bell states in different noisy channels by calculating concurrences.Our experimental results show that the concurrences of the different Bell states under the same artificial error operations have the same values within the experimental error,and are independent of the different Bell states.These experimental results verify the theoretical evolution equation developed by Konrad et al.[Nature Phys.4 (2008) 99]for two-qubit entanglement.
Simplified realization of two-qubit quantum phase gate with four-level systems in cavity QED
Yang, Chui-Ping; Chu, Shih-I.; Han, Siyuan
2004-10-01
We propose a method for realizing two-qubit quantum phase gate with 4-level systems in cavity QED. In this proposal, the two logical states of a qubit are represented by the two lowest levels of each system, and two intermediate levels of each system are utilized to facilitate coherent control and manipulation of quantum states of the qubits. The present method does not involve cavity-photon population during the operation. In addition, we show that the gate can be achieved using only two-step operations.
Influence of Intrinsic Decoherence on Entanglement in Two-Qubit Quantum Heisenberg XYZ Chain
Institute of Scientific and Technical Information of China (English)
SHAO Bin; ZENG Tian-Hai; ZOU Jian
2005-01-01
Taking the intrinsic decoherence effect into account, we investigate the time evolution of entanglement for two-qubit XYZ Heisenberg model in an external uniform magnetic field. Concurrence, the measurement of entanglement,is calculated. We show how the intrinsic decoherence modifies the time evolution of the entanglement and find that at short-time case, concurrence is oscillating as increasing magnetic field, which implies that entanglement may be enhanced or weakened in some time regions.
Institute of Scientific and Technical Information of China (English)
秦涛; 高克林
2003-01-01
We propose a scheme to implement a two-qubit Grover quantum search algorithm.The novelty in the proposal is that the motional state is introduced into the computation and the internal state within a single cold trapped ion.The motional and internal states of the ion are manipulated as two qubits by the laser pulses to accomplish an example of a Grover algorithm based on the two qubits.The composite laser pulses that are applied to implement the Grover algorithm have been designed in detail.The issues concerning measurement and decoherence are discussed.
Energy Technology Data Exchange (ETDEWEB)
Kato, Akihito, E-mail: kato@kuchem.kyoto-u.ac.jp; Tanimura, Yoshitaka, E-mail: tanimura@kuchem.kyoto-u.ac.jp [Department of Chemistry, Graduate School of Science, Kyoto University, Kyoto 606-8502 (Japan)
2015-08-14
We consider a system consisting of two interacting qubits that are individually coupled to separate heat baths at different temperatures. The quantum effects in heat transport are investigated in a numerically rigorous manner with a hierarchial equations of motion (HEOM) approach for non-perturbative and non-Markovian system-bath coupling cases under non-equilibrium steady-state conditions. For a weak interqubit interaction, the total system is regarded as two individually thermostatted systems, whereas for a strong interqubit interaction, the two-qubit system is regarded as a single system coupled to two baths. The roles of quantum coherence (or entanglement) between the two qubits (q-q coherence) and between the qubit and bath (q-b coherence) are studied through the heat current calculated for various strengths of the system-bath coupling and interqubit coupling for high and low temperatures. The same current is also studied using the time convolutionless (TCL) Redfield equation and using an expression derived from the Fermi golden rule (FGR). We find that the HEOM results exhibit turnover behavior of the heat current as a function of the system-bath coupling strength for all values of the interqubit coupling strength, while the results obtained with the TCL and FGR approaches do not exhibit such behavior, because they do not possess the capability of treating the q-b and q-q coherences. The maximum current is obtained in the case that the q-q coherence and q-b coherence are balanced in such a manner that coherence of the entire heat transport process is realized. We also find that the heat current does not follow Fourier’s law when the temperature difference is very large, due to the non-perturbative system-bath interactions.
Teleportation-based realization of an optical quantum two-qubit entangling gate
Gao, Wei-Bo; Lu, Chao-Yang; Dai, Han-Ning; Wagenknecht, Claudia; Zhang, Qiang; Zhao, Bo; Peng, Cheng-Zhi; Chen, Zeng-Bing; Chen, Yu-Ao; Pan, Jian-Wei
2010-01-01
In recent years, there has been heightened interest in quantum teleportation, which allows for the transfer of unknown quantum states over arbitrary distances. Quantum teleportation not only serves as an essential ingredient in long-distance quantum communication, but also provides enabling technologies for practical quantum computation. Of particular interest is the scheme proposed by Gottesman and Chuang [Nature \\textbf{402}, 390 (1999)], showing that quantum gates can be implemented by teleporting qubits with the help of some special entangled states. Therefore, the construction of a quantum computer can be simply based on some multi-particle entangled states, Bell state measurements and single-qubit operations. The feasibility of this scheme relaxes experimental constraints on realizing universal quantum computation. Using two different methods we demonstrate the smallest non-trivial module in such a scheme---a teleportation-based quantum entangling gate for two different photonic qubits. One uses a high-...
Liu, Tang-Kun; Tao, Yu; Shan, Chuan-Jia; Liu, Ji-bing
2017-10-01
Using the three criterions of the concurrence, the negative eigenvalue and the geometric quantum discord, we investigate the quantum entanglement and quantum correlation dynamics of two two-level atoms interacting with the coherent state optical field. We discuss the influence of different photon number of the mean square fluctuations on the temporal evolution of the concurrence, the negative eigenvalue and the geometric quantum discord between two atoms when the two atoms are initially in specific three states. The results show that different photon number of the mean square fluctuations can lead to different effects of quantum entanglement and quantum correlation dynamics.
Liu, Tang-Kun; Tao, Yu; Shan, Chuan-Jia; Liu, Ji-bing
2017-08-01
Using the three criterions of the concurrence, the negative eigenvalue and the geometric quantum discord, we investigate the quantum entanglement and quantum correlation dynamics of two two-level atoms interacting with the coherent state optical field. We discuss the influence of different photon number of the mean square fluctuations on the temporal evolution of the concurrence, the negative eigenvalue and the geometric quantum discord between two atoms when the two atoms are initially in specific three states. The results show that different photon number of the mean square fluctuations can lead to different effects of quantum entanglement and quantum correlation dynamics.
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.
Sun, Wen-Yang; Wang, Dong; Shi, Jia-Dong; Ye, Liu
2017-02-01
In this work, there are two parties, Alice on Earth and Bob on the satellite, which initially share an entangled state, and some open problems, which emerge during quantum steering that Alice remotely steers Bob, are investigated. Our analytical results indicate that all entangled pure states and maximally entangled evolution states (EESs) are steerable, and not every entangled evolution state is steerable and some steerable states are only locally correlated. Besides, quantum steering from Alice to Bob experiences a “sudden death” with increasing decoherence strength. However, shortly after that, quantum steering experiences a recovery with the increase of decoherence strength in bit flip (BF) and phase flip (PF) channels. Interestingly, while they initially share an entangled pure state, all EESs are steerable and obey Bell nonlocality in PF and phase damping channels. In BF channels, all steerable states can violate Bell-CHSH inequality, but some EESs are unable to be employed to realize steering. However, when they initially share an entangled mixed state, the outcome is different from that of the pure state. Furthermore, the steerability of entangled mixed states is weaker than that of entangled pure states. Thereby, decoherence can induce the degradation of quantum steering, and the steerability of state is associated with the interaction between quantum systems and reservoirs.
Sun, Wen-Yang; Wang, Dong; Shi, Jia-Dong; Ye, Liu
2017-01-01
In this work, there are two parties, Alice on Earth and Bob on the satellite, which initially share an entangled state, and some open problems, which emerge during quantum steering that Alice remotely steers Bob, are investigated. Our analytical results indicate that all entangled pure states and maximally entangled evolution states (EESs) are steerable, and not every entangled evolution state is steerable and some steerable states are only locally correlated. Besides, quantum steering from Alice to Bob experiences a “sudden death” with increasing decoherence strength. However, shortly after that, quantum steering experiences a recovery with the increase of decoherence strength in bit flip (BF) and phase flip (PF) channels. Interestingly, while they initially share an entangled pure state, all EESs are steerable and obey Bell nonlocality in PF and phase damping channels. In BF channels, all steerable states can violate Bell-CHSH inequality, but some EESs are unable to be employed to realize steering. However, when they initially share an entangled mixed state, the outcome is different from that of the pure state. Furthermore, the steerability of entangled mixed states is weaker than that of entangled pure states. Thereby, decoherence can induce the degradation of quantum steering, and the steerability of state is associated with the interaction between quantum systems and reservoirs. PMID:28145467
Investigations of the Quantum Correlation in Two-Qubit Heisenberg XYZ Model with Decoherence
Guo-Hui, Yang
2016-12-01
Quantum correlation dynamics in an anisotropic Heisenberg XYZ model under decoherence is investigated with the use of concurrence C and quantum discord (QD). With the Werner state as the initial state, we discuss the influence of mixture degree r on the dynamics. There are some difference between the time evolution behaviors of these two correlation measures with different value of r. For 0 ≤ r ≤ 1/3, there exists quantum discord but no entanglement; For 1/3
Quantum correlations in a two-qubit anisotropic Heisenberg XYZ chain with uniform magnetic field
Li, Lei; Yang, Guo-Hui
2014-07-01
Quantum correlations in an anisotropic Heisenberg XYZ chain is investigated by use of concurrence C and measurement-induced disturbance (MID). We show that the behaviors of the MID are remarkably different from the concurrence. Firstly, it is shown that there is a revival phenomenon in the concurrence but not in the MID, which is suitable for both the ground state case and the finite temperature case. Based on the analysis of the ground-state C and MID structures, we illustrate the reason why the ground-state MID does not show a revival phenomenon in detail. Then we explore different effects of the external and self parameters on entanglement and MID behaviors. It can be shown that the region of MID is evidently larger than the case of concurrence, and that the concurrence signals a quantum phase transition even at finite T while MID does not. Cases where the concurrence finally maintains one nonzero constant value regardless of the value of the variable B for a constant Jz, while MID decreases monotonously to zero with increasing B. We also show that if B can take a proper range of values, the concurrence decreases with the improvement of the anisotropic parameter γ, whereas an opposite effect for MID behaviors is presented.
Quantum state tomography for quadrupole nuclei and its applications on a two-qubit system
Energy Technology Data Exchange (ETDEWEB)
Bonk, F.A.; Azevedo, E.R. de; Mantovani, G.L.; Bonagamba, T.J. [Sao Paulo Univ., Sao Carlos, SP (Brazil). Inst. de Fisica]. E-mail: azevedo@if.sc.usp.br; Sarthour, R.S.; Bulnes, J.D.; Guimaraes, A.P.; Oliveira, I.S. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil)]. E-mails: sarthour@cbpf.br; apguima@cbpf.br; ivan@cbpf.br; Freitas, J.C.C. [Espirito Santo Univ., Vitoria (Brazil). Dept. de Fisica
2004-05-01
A method for performing quantum state tomography for quadrupole nuclei is presented in this paper. First, it is shown that upon appropriate phase cycling, the NMR intensities of quadrupole nuclei depend only on diagonal elements of the density matrix. Thus, a method for obtaining the density matrix elements, which consists of dragging off-diagonal elements into the main diagonal using fine phase-controlled selective radiofrequency pulses, was derived. The use of the method is exemplified through {sup 23} Na NMR (nuclear spin I = 3/2) in a lyotropic liquid-crystal at room temperature, in three applications: (a) the tomography of pseudo-pure states; (b) the tomography of the quadrupole free evolution of the density matrix, and (c) the unitary state evolution of each qubit in the system over the Bloch sphere upon the application of a Hadamard gate. Further applications in the context of pure NMR and in the context of quantum information processing, as well as generalizations for higher spins, are discussed. (author)
Quantum computer of wire circuit architecture
Moiseev, S A; Andrianov, S N
2010-01-01
First solid state quantum computer was built using transmons (cooper pair boxes). The operation of the computer is limited because of using a number of the rigit cooper boxes working with fixed frequency at temperatures of superconducting material. Here, we propose a novel architecture of quantum computer based on a flexible wire circuit of many coupled quantum nodes containing controlled atomic (molecular) ensembles. We demonstrate wide opportunities of the proposed computer. Firstly, we reveal a perfect storage of external photon qubits to multi-mode quantum memory node and demonstrate a reversible exchange of the qubits between any arbitrary nodes. We found optimal parameters of atoms in the circuit and self quantum modes for quantum processing. The predicted perfect storage has been observed experimentally for microwave radiation on the lithium phthalocyaninate molecule ensemble. Then also, for the first time we show a realization of the efficient basic two-qubit gate with direct coupling of two arbitrary...
Engineering extremal two-qubit entangled states with maximally entangled Gaussian light
Adesso, G; Illuminati, F; Paternostro, M
2010-01-01
We study state engineering induced by bilinear interactions between two remote qubits and light fields prepared in two-mode Gaussian states. The attainable two-qubit states span the entire physically allowed region in the entanglement-vs-global-purity plane. We show that two-mode Gaussian states with maximal entanglement at fixed global and marginal entropies produce maximally entangled two-qubit states in the corresponding entropic diagram. The target two-qubit entanglement is determined quantitatively only by the purities of the two-mode Gaussian resource. Thus, a small set of parameters characterizing extremally entangled two-mode Gaussian states is sufficient to control completely the engineering of extremally entangled two-qubit states, which can be realized in realistic scenarios of cavity and circuit quantum electrodynamics.
Ultrafast Quantum Gates in Circuit QED
Romero, G; Wang, Y M; Scarani, V; Solano, E
2011-01-01
We present a method of implementing ultrafast two-qubit gates valid for the ultrastrong coupling (USC) and deep strong coupling (DSC) regimes of light-matter interaction, considering state-of-the-art circuit quantum electrodynamics (QED) technology. Our proposal includes a suitable qubit architecture and is based on a four-step sequential displacement of an intracavity mode, operating at a time proportional to the inverse of the resonator frequency. Through ab initio calculations, we show that these quantum gates can be performed at subnanosecond time scales, while keeping the fidelity above 99%.
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.
Evolving Quantum Circuits using Genetic Algorithms
Prashant
2005-01-01
This paper describes an application of genetic algorithm for evolving quantum computing circuits. The circuits use reversible one qubit and two qubit gates which are applied on a multi-qubit system having some initial state. The genetic algorithm automatically searches the space and comes out with the appropriate circuit design, which yields desired output state. The fitness function used matches the output with desired output and the search stops when it is found. The fitness value becomes higher if the output is close to the desired output. The paper briefly discusses the operation of a quantum gate over the multi-qubit system. The paper also demonstrates some examples of the evolved circuits using the algorithm.
Hybrid quantum processors: molecular ensembles as quantum memory for solid state circuits.
Rabl, P; DeMille, D; Doyle, J M; Lukin, M D; Schoelkopf, R J; Zoller, P
2006-07-21
We investigate a hybrid quantum circuit where ensembles of cold polar molecules serve as long-lived quantum memories and optical interfaces for solid state quantum processors. The quantum memory realized by collective spin states (ensemble qubit) is coupled to a high-Q stripline cavity via microwave Raman processes. We show that, for convenient trap-surface distances of a few microm, strong coupling between the cavity and ensemble qubit can be achieved. We discuss basic quantum information protocols, including a swap from the cavity photon bus to the molecular quantum memory, and a deterministic two qubit gate. Finally, we investigate coherence properties of molecular ensemble quantum bits.
Hybrid Quantum Processors: molecular ensembles as quantum memory for solid state circuits
Rabl, P; Doyle, J M; Lukin, M D; Schölkopf, R J; Zoller, P
2006-01-01
We investigate a hybrid quantum circuit where ensembles of cold polar molecules serve as long-lived quantum memories and optical interfaces for solid state quantum processors. The quantum memory realized by collective spin states (ensemble qubit) is coupled to a high-Q stripline cavity via microwave Raman processes. We show that for convenient trap-surface distances of a few $\\mu$m, strong coupling between the cavity and ensemble qubit can be achieved. We discuss basic quantum information protocols, including a swap from the cavity photon bus to the molecular quantum memory, and a deterministic two qubit gate. Finally, we investigate coherence properties of molecular ensemble quantum bits.
Two qubits in the Dirac representation
Rajagopal, A. K.; Rendell, R. W.
2001-08-01
The Dirac-matrix representation of a general two-qubit system is shown to exhibit quite interesting features. The relativistic symmetries of time reversal T, charge conjugation C, parity P, and their products are reinterpreted here by examining their action on the Bell states. It is shown that only C does not mix the Bell states whereas all others do. The various logic gates of quantum information theory are also expressed in terms of the Dirac matrices. For example, the NOT gate is related to the product of T and P. A two-qubit density matrix is found to be entangled if it is invariant under C.
Quantum chemistry and charge transport in biomolecules with superconducting circuits
García-Álvarez, L.; Las Heras, U.; Mezzacapo, A.; Sanz, M.; Solano, E.; Lamata, L.
2016-06-01
We propose an efficient protocol for digital quantum simulation of quantum chemistry problems and enhanced digital-analog quantum simulation of transport phenomena in biomolecules with superconducting circuits. Along these lines, we optimally digitize fermionic models of molecular structure with single-qubit and two-qubit gates, by means of Trotter-Suzuki decomposition and Jordan-Wigner transformation. Furthermore, we address the modelling of system-environment interactions of biomolecules involving bosonic degrees of freedom with a digital-analog approach. Finally, we consider gate-truncated quantum algorithms to allow the study of environmental effects.
Quantum chemistry and charge transport in biomolecules with superconducting circuits
García-Álvarez, L.; Las Heras, U.; Mezzacapo, A.; Sanz, M.; Solano, E.; Lamata, L.
2016-01-01
We propose an efficient protocol for digital quantum simulation of quantum chemistry problems and enhanced digital-analog quantum simulation of transport phenomena in biomolecules with superconducting circuits. Along these lines, we optimally digitize fermionic models of molecular structure with single-qubit and two-qubit gates, by means of Trotter-Suzuki decomposition and Jordan-Wigner transformation. Furthermore, we address the modelling of system-environment interactions of biomolecules involving bosonic degrees of freedom with a digital-analog approach. Finally, we consider gate-truncated quantum algorithms to allow the study of environmental effects. PMID:27324814
Quantum chemistry and charge transport in biomolecules with superconducting circuits.
García-Álvarez, L; Las Heras, U; Mezzacapo, A; Sanz, M; Solano, E; Lamata, L
2016-06-21
We propose an efficient protocol for digital quantum simulation of quantum chemistry problems and enhanced digital-analog quantum simulation of transport phenomena in biomolecules with superconducting circuits. Along these lines, we optimally digitize fermionic models of molecular structure with single-qubit and two-qubit gates, by means of Trotter-Suzuki decomposition and Jordan-Wigner transformation. Furthermore, we address the modelling of system-environment interactions of biomolecules involving bosonic degrees of freedom with a digital-analog approach. Finally, we consider gate-truncated quantum algorithms to allow the study of environmental effects.
Two-qubit correlations via a periodic plasmonic nanostructure
Energy Technology Data Exchange (ETDEWEB)
Iliopoulos, Nikos; Terzis, Andreas F. [Department of Physics, School of Natural Sciences, University of Patras, Patras 265 04 (Greece); Yannopapas, Vassilios [Department of Physics, National Technical University of Athens, Athens 157 80 (Greece); Paspalakis, Emmanuel, E-mail: paspalak@upatras.gr [Materials Science Department, School of Natural Sciences, University of Patras, Patras 265 04 (Greece)
2016-02-15
We theoretically investigate the generation of quantum correlations by using two distant qubits in free space or mediated by a plasmonic nanostructure. We report both entanglement of formation as well as quantum discord and classical correlations. We have found that for proper initial state of the two-qubit system and distance between the two qubits we can produce quantum correlations taking significant value for a relatively large time interval so that it can be useful in quantum information and computation processes.
Parallelizing quantum circuit synthesis
Di Matteo, Olivia; Mosca, Michele
2016-01-01
Quantum circuit synthesis is the process in which an arbitrary unitary operation is decomposed into a sequence of gates from a universal set, typically one which a quantum computer can implement both efficiently and fault-tolerantly. As physical implementations of quantum computers improve, the need is growing for tools which can effectively synthesize components of the circuits and algorithms they will run. Existing algorithms for exact, multi-qubit circuit synthesis scale exponentially in t...
McCloskey, R.; Ferraro, A.; Paternostro, M.
2017-01-01
We identify the families of states that maximize some recently proposed quantifiers of Einstein-Podolsky-Rosen (EPR) steering and the volume of the quantum steering ellipsoid (QSE). The optimal measurements which maximize genuine EPR steering measures are discussed and we develop a way to find them using the QSE. We thus explore the links between genuine EPR steering and the QSE and introduce states that can be the most useful for one-sided device-independent quantum cryptography for a given amount of noise.
Quantum secure circuit evaluation
Institute of Scientific and Technical Information of China (English)
CHEN Huanhuan; LI Bin; ZHUANG Zhenquan
2004-01-01
In order to solve the problem of classical secure circuit evaluation, this paper proposes a quantum approach. In this approach, the method of inserting redundant entangled particles and quantum signature has been employed to strengthen the security of the system. Theoretical analysis shows that our solution is secure against classical and quantum attacks.
Experimental investigation of a four-qubit linear-optical quantum logic circuit
Stárek, R.; Mičuda, M.; Miková, M.; Straka, I.; Dušek, M.; Ježek, M.; Fiurášek, J.
2016-09-01
We experimentally demonstrate and characterize a four-qubit linear-optical quantum logic circuit. Our robust and versatile scheme exploits encoding of two qubits into polarization and path degrees of single photons and involves two crossed inherently stable interferometers. This approach allows us to design a complex quantum logic circuit that combines a genuine four-qubit C3Z gate and several two-qubit and single-qubit gates. The C3Z gate introduces a sign flip if and only if all four qubits are in the computational state |1>. We verify high-fidelity performance of this central four-qubit gate using Hofmann bounds on quantum gate fidelity and Monte Carlo fidelity sampling. We also experimentally demonstrate that the quantum logic circuit can generate genuine multipartite entanglement and we certify the entanglement with the use of suitably tailored entanglement witnesses.
Singh, Manu Pratap; Rajput, B. S.
2016-03-01
Recall operations of quantum associative memory (QuAM) have been conducted separately through evolutionary as well as non-evolutionary processes in terms of unitary and non- unitary operators respectively by separately choosing our recently derived maximally entangled states (Singh-Rajput MES) and Bell's MES as memory states for various queries and it has been shown that in each case the choices of Singh-Rajput MES as valid memory states are much more suitable than those of Bell's MES. it has been demonstrated that in both the types of recall processes the first and the fourth states of Singh-Rajput MES are most suitable choices as memory states for the queries `11' and `00' respectively while none of the Bell's MES is a suitable choice as valid memory state in these recall processes. It has been demonstrated that all the four states of Singh-Rajput MES are suitable choice as valid memory states for the queries `1?', `?1', `?0' and `0?' while none of the Bell's MES is suitable choice as the valid memory state for these queries also.
Orgiazzi, J.-L.; Deng, C.; Layden, D.; Marchildon, R.; Kitapli, F.; Shen, F.; Bal, M.; Ong, F. R.; Lupascu, A.
2016-03-01
We report experiments on superconducting flux qubits in a circuit quantum electrodynamics (cQED) setup. Two qubits, independently biased and controlled, are coupled to a coplanar waveguide resonator. Dispersive qubit state readout reaches a maximum contrast of 72%. We measure energy relaxation times at the symmetry point of 5 and 10 μ s , corresponding to 7 and 20 μ s when relaxation through the resonator due to Purcell effect is subtracted out, and levels of flux noise of 2.6 and 2.7 μ Φ0/√{Hz} at 1 Hz for the two qubits. We discuss the origin of decoherence in the measured devices. The strong coupling between the qubits and the cavity leads to a large, cavity-mediated, qubit-qubit coupling. This coupling, which is characterized spectroscopically, reaches 38 MHz. These results demonstrate the potential of cQED as a platform for fundamental investigations of decoherence and quantum dynamics of flux qubits.
Coxeter groups $A_{4}$, $B_{4}$ and $D_{4}$ for two-qubit systems
Indian Academy of Sciences (India)
Ramazan Koç; M Yakup Haciibrahimoğlu; Mehmet Koca
2013-08-01
The Coxeter–Weyl groups $W(A_{4})$, $W(B_{4})$ and $W(D_{4})$ have proven very useful for two-qubit systems in quantum information theory. A simple technique is employed to construct the unitary matrix representations of the groups, based on quaternionic transformation of the usual reflection matrices. The von Neumann entropy of each reduced density matrix is calculated. It is shown that these unitary matrix representations are naturally related to various universal quantum gates and they lead to entangled states. Canonical decomposition of generators in terms of fundamental gate representations is given to construct the quantum circuits.
Ultrafast quantum computation in ultrastrongly coupled circuit QED systems.
Wang, Yimin; Guo, Chu; Zhang, Guo-Qiang; Wang, Gangcheng; Wu, Chunfeng
2017-03-10
The latest technological progress of achieving the ultrastrong-coupling regime in circuit quantum electrodynamics (QED) systems has greatly promoted the developments of quantum physics, where novel quantum optics phenomena and potential computational benefits have been predicted. Here, we propose a scheme to accelerate the nontrivial two-qubit phase gate in a circuit QED system, where superconducting flux qubits are ultrastrongly coupled to a transmission line resonator (TLR), and two more TLRs are coupled to the ultrastrongly-coupled system for assistant. The nontrivial unconventional geometric phase gate between the two flux qubits is achieved based on close-loop displacements of the three-mode intracavity fields. Moreover, as there are three resonators contributing to the phase accumulation, the requirement of the coupling strength to realize the two-qubit gate can be reduced. Further reduction in the coupling strength to achieve a specific controlled-phase gate can be realized by adding more auxiliary resonators to the ultrastrongly-coupled system through superconducting quantum interference devices. We also present a study of our scheme with realistic parameters considering imperfect controls and noisy environment. Our scheme possesses the merits of ultrafastness and noise-tolerance due to the advantages of geometric phases.
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.
Optimal copying of entangled two-qubit states
Novotny, J; Jex, I
2004-01-01
We investigate the problem of copying pure two-qubit states of a given degree of entanglement in an optimal way. Completely positive covariant quantum operations are constructed which maximize the fidelity of the output states with respect to two separable copies. These optimal copying processes hint at the intricate relationship between fundamental laws of quantum theory and entanglement.
Local Random Quantum Circuits are Approximate Polynomial-Designs
Brandão, Fernando G. S. L.; Harrow, Aram W.; Horodecki, Michał
2016-09-01
We prove that local random quantum circuits acting on n qubits composed of O( t 10 n 2) many nearest neighbor two-qubit gates form an approximate unitary t-design. Previously it was unknown whether random quantum circuits were a t-design for any t > 3. The proof is based on an interplay of techniques from quantum many-body theory, representation theory, and the theory of Markov chains. In particular we employ a result of Nachtergaele for lower bounding the spectral gap of frustration-free quantum local Hamiltonians; a quasi-orthogonality property of permutation matrices; a result of Oliveira which extends to the unitary group the path-coupling method for bounding the mixing time of random walks; and a result of Bourgain and Gamburd showing that dense subgroups of the special unitary group, composed of elements with algebraic entries, are ∞-copy tensor-product expanders. We also consider pseudo-randomness properties of local random quantum circuits of small depth and prove that circuits of depth O( t 10 n) constitute a quantum t-copy tensor-product expander. The proof also rests on techniques from quantum many-body theory, in particular on the detectability lemma of Aharonov, Arad, Landau, and Vazirani. We give applications of the results to cryptography, equilibration of closed quantum dynamics, and the generation of topological order. In particular we show the following pseudo-randomness property of generic quantum circuits: Almost every circuit U of size O( n k ) on n qubits cannot be distinguished from a Haar uniform unitary by circuits of size O( n ( k-9)/11) that are given oracle access to U.
Solid state multi-ensemble quantum computer in waveguide circuit model
Moiseev, Sergey A; Gubaidullin, Firdus F
2010-01-01
The first realization of solid state quantum computer was demonstrated recently by using artificial atoms -- transmons in superconducting resonator. Here, we propose a novel architecture of flexible and scalable quantum computer based on a waveguide circuit coupling many quantum nodes of controlled atomic ensembles. For the first time, we found the optimal practically attainable parameters of the atoms and circuit for 100{%} efficiency of quantum memory for multi qubit photon fields and confirmed experimentally the predicted perfect storage. Then we revealed self modes for reversible transfer of qubits between the quantum memory node and arbitrary other nodes. We found a realization of iSWAP gate via direct coupling of two arbitrary nodes with a processing rate accelerated proportionally to number of atoms in the node. A large number of the two-qubit gates can be simultaneously realized in the circuit for implementation of parallel quantum processing. Dynamic coherent elimination procedure of excess quantum s...
Automated Design of Quantum Circuits
Williams, Colin P.; Gray, Alexander G.
2000-01-01
In order to design a quantum circuit that performs a desired quantum computation, it is necessary to find a decomposition of the unitary matrix that represents that computation in terms of a sequence of quantum gate operations. To date, such designs have either been found by hand or by exhaustive enumeration of all possible circuit topologies. In this paper we propose an automated approach to quantum circuit design using search heuristics based on principles abstracted from evolutionary genetics, i.e. using a genetic programming algorithm adapted specially for this problem. We demonstrate the method on the task of discovering quantum circuit designs for quantum teleportation. We show that to find a given known circuit design (one which was hand-crafted by a human), the method considers roughly an order of magnitude fewer designs than naive enumeration. In addition, the method finds novel circuit designs superior to those previously known.
Enhancing the fidelity of two-qubit gates by measurements
Gefen, Tuvia; Cohen, Daniel; Cohen, Itsik; Retzker, Alex
2017-03-01
Dynamical decoupling techniques are the method of choice for increasing gate fidelities. While these methods have produced very impressive results in terms of decreasing local noise and increasing the fidelities of single-qubit operations, dealing with the noise of two-qubit gates has proven more challenging. The main obstacle is that the noise time scale is shorter than the two-qubit gate itself, so that refocusing methods do not work. We present a measurement- and feedback-based method to suppress two-qubit-gate noise, which cannot be suppressed by conventional methods. We analyze in detail this method for an error model, which is relevant for trapped-ion quantum information.
Two Qubits in the Dirac Representation
Rajagopal, A K
2000-01-01
A general two qubit system expressed in terms of the complete set of unit and fifteen traceless, Hermitian Dirac matrices, is shown to exhibit novel features of this system. The well-known physical interpretations associated with the relativistic Dirac equation involving the symmetry operations of time-reversal T, charge conjugation C, parity P, and their products are reinterpreted here by examining their action on the basic Bell states. The transformation properties of the Bell basis states under these symmetry operations also reveal that C is the only operator that does not mix the Bell states whereas all others do. In a similar fashion, expressing the various logic gates introduced in the subject of quantum computers in terms of the Dirac matrices shows for example, that the NOT gate is related to the product of time-reversal and parity operators.
Projective Ring Line Encompassing Two-Qubits
Saniga, M; Pracna, P; Planat, Michel; Pracna, Petr; Saniga, Metod
2006-01-01
The projective line over the (non-commutative) ring of two-by-two matrices with coefficients in GF(2) is found to fully accommodate the algebra of 15 operators -- generalized Pauli matrices -- characterizing two-qubit systems. The relevant sub-configuration consits of 15 points each of which is either simultaneusly distant or simultaneously neighbour to (any) two given distant points of the line. The operators can be identified with the points in such a one-to-one manner that their commutation relations are exactly reproduced by the underlying geometry of the points, with the ring geometrical notions of neighbour/distant answering, respectively, to the operational ones of commuting/non-commuting. This finding opens up rather unexpected vistas for an algebraic geometrical modelling of finite-dimensional quantum systems and gives their numerous applications a wholy new perspective.
A Practical Top-down Approach to Quantum Circuit Synthesis
Shende, V V; Markov, I L
2004-01-01
Operators acting on a collection of two-level quantum-mechanical systems can be represented by quantum circuits. In this work we develop a decomposition of such unitary operators which reveals their top-down structure and can be implemented numerically with well-known primitives. It leads to simultaneous improvements by a factor of two over (i) the best known n-qubit circuit synthesis algorithms for large n, and (ii) the best known three-qubit circuits. In the worst case, our algorithm NQ produces circuits that differ from known lower bounds by approximately a factor of two. Thus, the required number of quantum controlled-not's (i.e. two-qubit interactions) is only half of the number of real degrees of freedom (4^n-1) of a generic unitary operator. This is desirable since CNOTs are typically slower and more error-prone than one-qubit rotations, and they may in addition may require physically coupling distant two-level systems.
Effect of Multiphoton Processes on Geometric Quantum Computation in Superconducting Circuit QED
Institute of Scientific and Technical Information of China (English)
CHEN Chang-Yong
2012-01-01
We study the influence of multi-photon processes on the geometric quantum computation in the systems of superconducting qubits based on the displacement-like and the general squeezed operator methods. As an example, we focus on the question about how to implement a two-qubit geometric phase gate using superconducting circuit quantum electrodynamics with both single- and two-photon interaction between the qubits and the cavity modes. We find that the multiphoton processes are not only controllable but also improve the gating speed. The comparison with other physical systems and experimental feasibility are discussed in detail.
One-step quantum phase gate in the ultrastrong coupling regime of circuit QED
Xu, Xuexin; Liu, Xin; Liao, Qinghong; Zhou, Keya; Liu, Shutian
2017-09-01
In a previous publication (Phys Rev Lett 108: 120501, 2012), Romero et al. proposed an ultrastrong coupling circuit QED system that can implement a two-qubit quantum phase gate with four controlling pulses. Based on this architecture, we demonstrate that an ultrafast two-qubit phase gate can also be realized with only one oscillation and lower coupling strengths. In our operation scheme, two identical qubits evolve synchronously under a single pulse with a duration determined by a specific coupling strength. The phase gate can also be obtained periodically. The influences of parameter fluctuations are estimated. We demonstrate that the fidelities can be greater than 99% if the parameter fluctuations are controlled within 5%.
Implementation of a quantum controlled-SWAP gate with photonic circuits
Ono, Takafumi; Okamoto, Ryo; Tanida, Masato; Hofmann, Holger F.; Takeuchi, Shigeki
2017-01-01
Quantum information science addresses how the processing and transmission of information are affected by uniquely quantum mechanical phenomena. Combination of two-qubit gates has been used to realize quantum circuits, however, scalability is becoming a critical problem. The use of three-qubit gates may simplify the structure of quantum circuits dramatically. Among them, the controlled-SWAP (Fredkin) gates are essential since they can be directly applied to important protocols, e.g., error correction, fingerprinting, and optimal cloning. Here we report a realization of the Fredkin gate for photonic qubits. We achieve a fidelity of 0.85 in the computational basis and an output state fidelity of 0.81 for a 3-photon Greenberger-Horne-Zeilinger state. The estimated process fidelity of 0.77 indicates that our Fredkin gate can be applied to various quantum tasks. PMID:28361950
Di Vincenzo, D P
1997-01-01
A historical review is given of the emergence of the idea of the quantum logic gate from the theory of reversible Boolean gates. I highlight the quantum XOR or controlled NOT as the fundamental two-bit gate for quantum computation. This gate plays a central role in networks for quantum error correction.
Entangled Bloch Spheres: Bloch Matrix And Two Qubit State Space
Gamel, Omar
2016-01-01
We represent a two qubit density matrix in the basis of Pauli matrix tensor products, with the coefficients constituting a Bloch matrix, analogous to the single qubit Bloch vector. We find the quantum state positivity requirements on the Bloch matrix components, leading to three important inequalities, allowing us to parameterize and visualize the two qubit state space. Applying the singular value decomposition naturally separates the degrees of freedom to local and nonlocal, and simplifies the positivity inequalities. It also allows us to geometrically represent a state as two entangled Bloch spheres with superimposed correlation axes. It is shown that unitary transformations, local or nonlocal, have simple interpretations as axis rotations or mixing of certain degrees of freedom. The nonlocal unitary invariants of the state are then derived in terms of local unitary invariants. The positive partial transpose criterion for entanglement is generalized, and interpreted as a reflection, or a change of a single ...
Two qubits of a W state violate Bell's inequality beyond Cirel'son's bound
Cabello, A
2002-01-01
It is shown that the correlations between two qubits selected from a trio prepared in a W state violate the Clauser-Horne-Shimony-Holt inequality more than the correlations between two qubits in any quantum state. Such a violation beyond Cirel'son's bound is smaller than the one achieved by two qubits selected from a trio in a Greenberger-Horne-Zeilinger state [A. Cabello, Phys. Rev. Lett. 88, 060403 (2002)]. However, it has the advantage that all local observers can know from their own measurements whether their qubits belongs or not to the selected pair.
Wang, Hao; Wu, Guoxing; Chen, Daojiong
2012-07-01
Based on the isotropic two spin-1/2 qubits Heisenberg model with Dzyaloshinskii-Moriya interaction in a constant external magnetic field, we have constructed the entangled quantum Otto engine. Expressions for the basic thermodynamic quantities, i.e. the amount of heat exchange, the net work output and the efficiency, are derived. The influence of thermal entanglement on these basic thermodynamic quantities is investigated. Moreover, some intriguing features and their qualitative explanations in zero and finite magnetic field are given. The validity of the second law of thermodynamics is confirmed in the system. The results obtained here have general significance and will be useful in increasing understanding of the performance of an entangled quantum engine.
Energy Technology Data Exchange (ETDEWEB)
Akibue, Seiseki [Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo (Japan); Murao, Mio [Department of Physics, Graduate School of Science, The University of Tokyo, Tokyo, Japan and NanoQuine, The University of Tokyo, Tokyo (Japan)
2014-12-04
We investigate distributed implementation of two-qubit unitary operations over two primitive networks, the butterfly network and the ladder network, as a first step to apply network coding for quantum computation. By classifying two-qubit unitary operations in terms of the Kraus-Cirac number, the number of non-zero parameters describing the global part of two-qubit unitary operations, we analyze which class of two-qubit unitary operations is implementable over these networks with free classical communication. For the butterfly network, we show that two classes of two-qubit unitary operations, which contain all Clifford, controlled-unitary and matchgate operations, are implementable over the network. For the ladder network, we show that two-qubit unitary operations are implementable over the network if and only if their Kraus-Cirac number do not exceed the number of the bridges of the ladder.
Assisted Cloning and Orthogonal Complementing of an Arbitrary Unknown Two-Qubit Entangled State
Institute of Scientific and Technical Information of China (English)
FANG Ming; LIU Yi-Min; LIU Jun; SHI Shou-Hua; ZHANG Zhan-Jun
2006-01-01
Based on A.K. Pati's original idea [Phys. Rev. A 61 (2000) 022308] on single-qubit-state-assisted clone, very recently Zhan has proposed two assisted quantum cloning protocols of a special class of unknown two-qubit entangled states [Phys. Lett. A 336 (2005) 317]. In this paper we further generalize Zhan's protocols such that an arbitrary unknown two-qubit entangled state can be treated.
Yang, Guowu; Song, Xiaoyu; Perkowski, Marek
2011-01-01
We propose an approach to optimally synthesize quantum circuits from non-permutative quantum gates such as Controlled-Square-Root-of-Not (i.e. Controlled-V). Our approach reduces the synthesis problem to multiple-valued optimization and uses group theory. We devise a novel technique that transforms the quantum logic synthesis problem from a multi-valued constrained optimization problem to a group permutation problem. The transformation enables us to utilize group theory to exploit the properties of the synthesis problem. Assuming a cost of one for each two-qubit gate, we found all reversible circuits with quantum costs of 4, 5, 6, etc, and give another algorithm to realize these reversible circuits with quantum gates.
Superconducting Quantum Circuits
Majer, J.B.
2002-01-01
This thesis describes a number of experiments with superconducting cir- cuits containing small Josephson junctions. The circuits are made out of aluminum islands which are interconnected with a very thin insulating alu- minum oxide layer. The connections form a Josephson junction. The current trough
Quantum Memristors with Superconducting Circuits
Salmilehto, J.; Deppe, F.; di Ventra, M.; Sanz, M.; Solano, E.
2017-02-01
Memristors are resistive elements retaining information of their past dynamics. They have garnered substantial interest due to their potential for representing a paradigm change in electronics, information processing and unconventional computing. Given the advent of quantum technologies, a design for a quantum memristor with superconducting circuits may be envisaged. Along these lines, we introduce such a quantum device whose memristive behavior arises from quasiparticle-induced tunneling when supercurrents are cancelled. For realistic parameters, we find that the relevant hysteretic behavior may be observed using current state-of-the-art measurements of the phase-driven tunneling current. Finally, we develop suitable methods to quantify memory retention in the system.
Quantum Memristors with Superconducting Circuits
Salmilehto, J.; Deppe, F.; Di Ventra, M.; Sanz, M.; Solano, E.
2017-01-01
Memristors are resistive elements retaining information of their past dynamics. They have garnered substantial interest due to their potential for representing a paradigm change in electronics, information processing and unconventional computing. Given the advent of quantum technologies, a design for a quantum memristor with superconducting circuits may be envisaged. Along these lines, we introduce such a quantum device whose memristive behavior arises from quasiparticle-induced tunneling when supercurrents are cancelled. For realistic parameters, we find that the relevant hysteretic behavior may be observed using current state-of-the-art measurements of the phase-driven tunneling current. Finally, we develop suitable methods to quantify memory retention in the system. PMID:28195193
Entanglement Dynamics of Two Qubits Coupled to a Noise Environmen
Institute of Scientific and Technical Information of China (English)
LIU Jin; XIANG Shao-Hua; CUI Hui-Ping; LI Jian
2009-01-01
We study the time evolution of two two-state systems (two qubits) initially in the pure entangled states or the maximally entangled mixed states interacting with the individual environmental noise.It is shown that due to environment noise, all quantum entangled states axe very fragile and become a classical mixed state in a short-time limit.But the environment can affect entanglement in very different ways.The type of decoherence process for certain entangled states belongs to amplitude damping, while the others belong to dephasing decoherence.
Note on Entanglement of an Arbitrary State of Two Qubits
Institute of Scientific and Technical Information of China (English)
WANG An-Min
2000-01-01
It is shown that the norm of the polarization vector of the reduced density matrix can characterize the entangle ment of two qubits and so it is defined as a simple measure of entanglement. It is then extended to the generalized entanglement of polarization vector. It is proved that the entanglement of formation belongs to the generalized entanglement of polarization vector. Under the local general measurement and classical communication how this generalized entanglement of polarization vector changes is proved strictly and so the first and second laws of quantum information processing are verified clearly.
Del Duce, A; Bayvel, P
2009-01-01
We analyse the design and optimisation of quantum logic circuits suitable for the experimental demonstration of a three-qubit quantum computation prototype based on optically-controlled, solid-state quantum logic gates. In these gates, the interaction between two qubits carried by the electron-spin of donors is mediated by the optical excitation of a control particle placed in their proximity. First, we use a geometrical approach for analysing the entangling characteristics of these quantum gates. Then, using a genetic programming algorithm, we develop circuits for the refined Deutsch-Jozsa algorithm investigating different strategies for obtaining short total computational times. We test two separate approaches based on using different sets of entangling gates with the shortest possible gate computation time which, however, does not introduce leakage of quantum information to the control particles. The first set exploits fast approximations of controlled-phase gates as entangling gates, while the other one a...
Coulomb drag in quantum circuits
Levchenko, Alex; Kamenev, Alex
2008-01-01
We study drag effect in a system of two electrically isolated quantum point contacts (QPC), coupled by Coulomb interactions. Drag current exhibits maxima as a function of QPC gate voltages when the latter are tuned to the transitions between quantized conductance plateaus. In the linear regime this behavior is due to enhanced electron-hole asymmetry near an opening of a new conductance channel. In the non-linear regime the drag current is proportional to the shot noise of the driving circuit,...
Observation of topological transitions in interacting quantum circuits.
Roushan, P; Neill, C; Chen, Yu; Kolodrubetz, M; Quintana, C; Leung, N; Fang, M; Barends, R; Campbell, B; Chen, Z; Chiaro, B; Dunsworth, A; Jeffrey, E; Kelly, J; Megrant, A; Mutus, J; O'Malley, P J J; Sank, D; Vainsencher, A; Wenner, J; White, T; Polkovnikov, A; Cleland, A N; Martinis, J M
2014-11-13
Topology, with its abstract mathematical constructs, often manifests itself in physics and has a pivotal role in our understanding of natural phenomena. Notably, the discovery of topological phases in condensed-matter systems has changed the modern conception of phases of matter. The global nature of topological ordering, however, makes direct experimental probing an outstanding challenge. Present experimental tools are mainly indirect and, as a result, are inadequate for studying the topology of physical systems at a fundamental level. Here we employ the exquisite control afforded by state-of-the-art superconducting quantum circuits to investigate topological properties of various quantum systems. The essence of our approach is to infer geometric curvature by measuring the deflection of quantum trajectories in the curved space of the Hamiltonian. Topological properties are then revealed by integrating the curvature over closed surfaces, a quantum analogue of the Gauss-Bonnet theorem. We benchmark our technique by investigating basic topological concepts of the historically important Haldane model after mapping the momentum space of this condensed-matter model to the parameter space of a single-qubit Hamiltonian. In addition to constructing the topological phase diagram, we are able to visualize the microscopic spin texture of the associated states and their evolution across a topological phase transition. Going beyond non-interacting systems, we demonstrate the power of our method by studying topology in an interacting quantum system. This required a new qubit architecture that allows for simultaneous control over every term in a two-qubit Hamiltonian. By exploring the parameter space of this Hamiltonian, we discover the emergence of an interaction-induced topological phase. Our work establishes a powerful, generalizable experimental platform to study topological phenomena in quantum systems.
Adiabatic and Hamiltonian computing on a 2D lattice with simple two-qubit interactions
Lloyd, Seth; Terhal, Barbara M.
2016-02-01
We show how to perform universal Hamiltonian and adiabatic computing using a time-independent Hamiltonian on a 2D grid describing a system of hopping particles which string together and interact to perform the computation. In this construction, the movement of one particle is controlled by the presence or absence of other particles, an effective quantum field effect transistor that allows the construction of controlled-NOT and controlled-rotation gates. The construction translates into a model for universal quantum computation with time-independent two-qubit ZZ and XX+YY interactions on an (almost) planar grid. The effective Hamiltonian is arrived at by a single use of first-order perturbation theory avoiding the use of perturbation gadgets. The dynamics and spectral properties of the effective Hamiltonian can be fully determined as it corresponds to a particular realization of a mapping between a quantum circuit and a Hamiltonian called the space-time circuit-to-Hamiltonian construction. Because of the simple interactions required, and because no higher-order perturbation gadgets are employed, our construction is potentially realizable using superconducting or other solid-state qubits.
Efficient Scheme for Optimizing Quantum Fourier Circuits
Institute of Scientific and Technical Information of China (English)
JIANG Min; ZHANG Zengke; Tzyh-Jong Tarn
2008-01-01
In quantum circuits, importing of additional qubits can reduce the operation time and prevent de-coherence induced by the environment. However, excessive qubits may make the quantum system vulner-able. This paper describes how to relax existing qubits without additional qubits to significantly reduce the operation time of the quantum Fourier circuit compared to a circuit without optimization. The results indicate that this scheme makes full use of the qubits relaxation. The concepts can be applied to improve similar quantum circuits and guide the physical implementations of quantum algorithms or devices.
Tomographic causal analysis of two-qubit states and tomographic discord
Energy Technology Data Exchange (ETDEWEB)
Kiktenko, Evgeny [Bauman Moscow State Technical University, 2nd Baumanskaya St., 5, Moscow 105005 (Russian Federation); Geoelectromagnetic Research Center of Schmidt Institute of Physics of the Earth, Russian Academy of Sciences, PO Box 30, Troitsk, Moscow Region 142190 (Russian Federation); Fedorov, Aleksey, E-mail: akf@rqc.ru [Bauman Moscow State Technical University, 2nd Baumanskaya St., 5, Moscow 105005 (Russian Federation); Russian Quantum Center, Novaya St. 100, Skolkovo, Moscow 143025 (Russian Federation)
2014-05-01
We study a behavior of two-qubit states subject to tomographic measurement. In this Letter we propose a novel approach to definition of asymmetry in quantum bipartite state based on its tomographic Shannon entropies. We consider two types of measurement bases: the first is one that diagonalizes density matrices of subsystems and is used in a definition of tomographic discord, and the second is one that maximizes Shannon mutual information and relates to symmetrical form quantum discord. We show how these approaches relate to each other and then implement them to the different classes of two-qubit states. Consequently, new subclasses of X-states are revealed.
Relative Entropy of Entanglement of One Class of Two-Qubit System
Institute of Scientific and Technical Information of China (English)
LIANG Lin-Mei; CHEN Ping-Xing; LI Cheng-Zu; HUANG Ming-Qiu
2001-01-01
The relative entropy of entanglement of a mixed state σ for a bipartite quantum system can be defined as the minimum of the quantum relative entropy over the set of completely disentangled states. Vedral et al. [Phys.Rev. A 57(1998)1619] have recently proposed a numerical method to obtain the relative entropy of entanglement Ere for two-qubit systems. This letter shows that the convex programming method can be applied to calculate Ere of two-qubit systems analytically, and discusses the conditions under which the method can be adopted.
Quantum Computation Beyond the Circuit Model
Jordan, Stephen P.
2008-01-01
The quantum circuit model is the most widely used model of quantum computation. It provides both a framework for formulating quantum algorithms and an architecture for the physical construction of quantum computers. However, several other models of quantum computation exist which provide useful alternative frameworks for both discovering new quantum algorithms and devising new physical implementations of quantum computers. In this thesis, I first present necessary background material for a ge...
Physical synthesis of quantum circuits using templates
Mirkhani, Zahra; Mohammadzadeh, Naser
2016-10-01
Similar to traditional CMOS circuits, quantum circuit design flow is divided into two main processes: logic synthesis and physical design. Addressing the limitations imposed on optimization of the quantum circuit metrics because of no information sharing between logic synthesis and physical design processes, the concept of " physical synthesis" was introduced for quantum circuit flow, and a few techniques were proposed for it. Following that concept, in this paper a new approach for physical synthesis inspired by template matching idea in quantum logic synthesis is proposed to improve the latency of quantum circuits. Experiments show that by using template matching as a physical synthesis approach, the latency of quantum circuits can be improved by more than 23.55 % on average.
Gate-Level Simulation of Quantum Circuits
Viamontes, G F; Markov, I L; Hayes, J P; Viamontes, George F.; Rajagopalan, Manoj; Markov, Igor L.; Hayes, John P.
2002-01-01
While thousands of experimental physicists and chemists are currently trying to build scalable quantum computers, it appears that simulation of quantum computation will be at least as critical as circuit simulation in classical VLSI design. However, since the work of Richard Feynman in the early 1980s little progress was made in practical quantum simulation. Most researchers focused on polynomial-time simulation of restricted types of quantum circuits that fall short of the full power of quantum computation. Simulating quantum computing devices and useful quantum algorithms on classical hardware now requires excessive computational resources, making many important simulation tasks infeasible. In this work we propose a new technique for gate-level simulation of quantum circuits which greatly reduces the difficulty and cost of such simulations. The proposed technique is implemented in a simulation tool called the Quantum Information Decision Diagram (QuIDD) and evaluated by simulating Grover's quantum search al...
Wire recycling for quantum circuit optimization
Paler, Alexandru; Wille, Robert; Devitt, Simon J.
2016-10-01
Quantum information processing is expressed using quantum bits (qubits) and quantum gates which are arranged in terms of quantum circuits. Here, each qubit is associated with a quantum circuit wire which is used to conduct the desired operations. Most of the existing quantum circuits allocate a single quantum circuit wire for each qubit and hence introduce significant overhead. In fact, qubits are usually not needed during the entire computation, only between their initialization and measurement. Before and after that, corresponding wires may be used by other qubits. In this work, we propose a solution which exploits this fact in order to optimize the design of quantum circuits with respect to the required wires. To this end, we introduce a representation of the lifetimes of all qubits which is used to analyze the respective need for wires. Based on this analysis, a method is proposed which "recycles" the available wires and, as a result, reduces the size of the resulting circuit. Numerical tests based on established reversible and fault-tolerant quantum circuits confirm that the proposed solution reduces the number of wires by more than 90% compared to unoptimized quantum circuits.
Reversible and quantum circuits optimization and complexity analysis
Abdessaied, Nabila
2016-01-01
This book presents a new optimization flow for quantum circuits realization. At the reversible level, optimization algorithms are presented to reduce the quantum cost. Then, new mapping approaches to decompose reversible circuits to quantum circuits using different quantum libraries are described. Finally, optimization techniques to reduce the quantum cost or the delay are applied to the resulting quantum circuits. Furthermore, this book studies the complexity of reversible circuits and quantum circuits from a theoretical perspective.
The Veldkamp Space of Two-Qubits
Directory of Open Access Journals (Sweden)
Metod Saniga
2007-06-01
Full Text Available Given a remarkable representation of the generalized Pauli operators of two-qubits in terms of the points of the generalized quadrangle of order two, W(2, it is shown that specific subsets of these operators can also be associated with the points and lines of the four-dimensional projective space over the Galois field with two elements - the so-called Veldkamp space of W(2. An intriguing novelty is the recognition of (uni- and tri-centric triads and specific pentads of the Pauli operators in addition to the ''classical'' subsets answering to geometric hyperplanes of W(2.
Realization of Quantum Circuits in Fock Space
Institute of Scientific and Technical Information of China (English)
MA Lei; LI Yun
2004-01-01
In this letter, by using the method we offered in our paper [L. Ma and Y.D. Zhang, Commun. Theor. Phys.(Beijing, China) 36 (2001) 119], some extended quantum logic gates, such as quantum counter, quantum adder, are studied and their expressions are given. It may be useful for us to study the more complicated quantum logic circuits deeply.
Superconducting quantum circuits at the surface code threshold for fault tolerance.
Barends, R; Kelly, J; Megrant, A; Veitia, A; Sank, D; Jeffrey, E; White, T C; Mutus, J; Fowler, A G; Campbell, B; Chen, Y; Chen, Z; Chiaro, B; Dunsworth, A; Neill, C; O'Malley, P; Roushan, P; Vainsencher, A; Wenner, J; Korotkov, A N; Cleland, A N; Martinis, John M
2014-04-24
A quantum computer can solve hard problems, such as prime factoring, database searching and quantum simulation, at the cost of needing to protect fragile quantum states from error. Quantum error correction provides this protection by distributing a logical state among many physical quantum bits (qubits) by means of quantum entanglement. Superconductivity is a useful phenomenon in this regard, because it allows the construction of large quantum circuits and is compatible with microfabrication. For superconducting qubits, the surface code approach to quantum computing is a natural choice for error correction, because it uses only nearest-neighbour coupling and rapidly cycled entangling gates. The gate fidelity requirements are modest: the per-step fidelity threshold is only about 99 per cent. Here we demonstrate a universal set of logic gates in a superconducting multi-qubit processor, achieving an average single-qubit gate fidelity of 99.92 per cent and a two-qubit gate fidelity of up to 99.4 per cent. This places Josephson quantum computing at the fault-tolerance threshold for surface code error correction. Our quantum processor is a first step towards the surface code, using five qubits arranged in a linear array with nearest-neighbour coupling. As a further demonstration, we construct a five-qubit Greenberger-Horne-Zeilinger state using the complete circuit and full set of gates. The results demonstrate that Josephson quantum computing is a high-fidelity technology, with a clear path to scaling up to large-scale, fault-tolerant quantum circuits.
Concurrence Measurement for the Two-Qubit Optical and Atomic States
Directory of Open Access Journals (Sweden)
Lan Zhou
2015-06-01
Full Text Available Concurrence provides us an effective approach to quantify entanglement, which is quite important in quantum information processing applications. In the paper, we mainly review some direct concurrence measurement protocols of the two-qubit optical or atomic system. We first introduce the concept of concurrence for a two-qubit system. Second, we explain the approaches of the concurrence measurement in both a linear and a nonlinear optical system. Third, we introduce some protocols for measuring the concurrence of the atomic entanglement system.
Teleportation via thermally entangled states of a two-qubit Heisenberg XXZ chain
Institute of Scientific and Technical Information of China (English)
QIN Meng; TAO Ying-Juan; TIAN Dong-Ping
2008-01-01
We investigate quantum teleportation as a tool to study the thermally entangled state of a twoqubit Heisenberg XXZ chain.Our work is mainly to investigate the characteristics of a Heisenberg XXZ chain and get some analytical results of the fully entangled fraction.We also consider the entanglement teleportation via a two-qubit Heisenberg XXZ chain.
Multilayer microwave integrated quantum circuits for scalable quantum computing
Brecht, Teresa; Pfaff, Wolfgang; Wang, Chen; Chu, Yiwen; Frunzio, Luigi; Devoret, Michel H.; Schoelkopf, Robert J.
2016-02-01
As experimental quantum information processing (QIP) rapidly advances, an emerging challenge is to design a scalable architecture that combines various quantum elements into a complex device without compromising their performance. In particular, superconducting quantum circuits have successfully demonstrated many of the requirements for quantum computing, including coherence levels that approach the thresholds for scaling. However, it remains challenging to couple a large number of circuit components through controllable channels while suppressing any other interactions. We propose a hardware platform intended to address these challenges, which combines the advantages of integrated circuit fabrication and the long coherence times achievable in three-dimensional circuit quantum electrodynamics. This multilayer microwave integrated quantum circuit platform provides a path towards the realisation of increasingly complex superconducting devices in pursuit of a scalable quantum computer.
Intrinsic Decoherence on Two-Qubit Heisenberg ⅩⅩ Chain
Institute of Scientific and Technical Information of China (English)
HE Zheng-Hong; XIONG Zu-Hong; HU Dong-Mei
2007-01-01
Quantum teleportation is investigated by using the entangled states of two-qubit Heisenberg ⅩⅩ chain in an external uniform magnetic field as resources in the model of Milburn's intrinsic decoherence. Though intrinsic decoherence on quantum entanglement and quantum teleportation exerts different effects in different initial systems,proper magnetic fields and probabilities of different eigenstates in the initial states can weaken the effects.
Feedback control of superconducting quantum circuits
Ristè, D.
2014-01-01
Superconducting circuits have recently risen to the forefront of the solid-state prototypes for quantum computing. Reaching the stage of robust quantum computing requires closing the loop between measurement and control of quantum bits (qubits). This thesis presents the realization of feedback contr
Optimal two qubit gate for generation of random bipartite entanglement
Znidaric, M
2007-01-01
We study protocols for generation of random pure states consisting of repeated applications of two qubit transformations. Necessary number of steps needed in order to generate states displaying bipartite entanglement typical of random states is obtained. We also find the optimal two qubit gate for which the convergence is the fastest. Perhaps surprisingly, applying the same good two qubit gate in addition to a random single qubit rotations at each step leads to a faster generation of entanglement than applying a random two qubit transformation at each step.
Quantum Networks with Chiral-Light-Matter Interaction in Waveguides
Mahmoodian, Sahand; Lodahl, Peter; Sørensen, Anders S.
2016-12-01
We propose a scalable architecture for a quantum network based on a simple on-chip photonic circuit that performs loss-tolerant two-qubit measurements. The circuit consists of two quantum emitters positioned in the arms of an on-chip Mach-Zehnder interferometer composed of waveguides with chiral-light-matter interfaces. The efficient chiral-light-matter interaction allows the emitters to perform high-fidelity intranode two-qubit parity measurements within a single chip and to emit photons to generate internode entanglement, without any need for reconfiguration. We show that, by connecting multiple circuits of this kind into a quantum network, it is possible to perform universal quantum computation with heralded two-qubit gate fidelities F ˜0.998 achievable in state-of-the-art quantum dot systems.
Two Qubits Entanglement Dynamics in 1D Heisenberg Chain with Intrinsic Decoherence
Institute of Scientific and Technical Information of China (English)
SHAO Bin; ZHANG Li-li; ZOU Jian
2006-01-01
To reveal how the decoherence modifies the time evolution of the entanglement of quantum system,the intrinsic decoherence approach and the entanglement of formation are used, and the time evolution of entanglement for two-qubit 1D quantum Heisenberg model in an external uniform magnetic field is derived. It is shown that the external magnetic field can strengthen the effects of the intrinsic decoherence on the entanglement of the system.
Superconducting quantum circuits theory and application
Deng, Xiuhao
Superconducting quantum circuit models are widely used to understand superconducting devices. This thesis consists of four studies wherein the superconducting quantum circuit is used to illustrate challenges related to quantum information encoding and processing, quantum simulation, quantum signal detection and amplification. The existence of scalar Aharanov-Bohm phase has been a controversial topic for decades. Scalar AB phase, defined as time integral of electric potential, gives rises to an extra phase factor in wavefunction. We proposed a superconducting quantum Faraday cage to detect temporal interference effect as a consequence of scalar AB phase. Using the superconducting quantum circuit model, the physical system is solved and resulting AB effect is predicted. Further discussion in this chapter shows that treating the experimental apparatus quantum mechanically, spatial scalar AB effect, proposed by Aharanov-Bohm, can't be observed. Either a decoherent interference apparatus is used to observe spatial scalar AB effect, or a quantum Faraday cage is used to observe temporal scalar AB effect. The second study involves protecting a quantum system from losing coherence, which is crucial to any practical quantum computation scheme. We present a theory to encode any qubit, especially superconducting qubits, into a universal quantum degeneracy point (UQDP) where low frequency noise is suppressed significantly. Numerical simulations for superconducting charge qubit using experimental parameters show that its coherence time is prolong by two orders of magnitude using our universal degeneracy point approach. With this improvement, a set of universal quantum gates can be performed at high fidelity without losing too much quantum coherence. Starting in 2004, the use of circuit QED has enabled the manipulation of superconducting qubits with photons. We applied quantum optical approach to model coupled resonators and obtained a four-wave mixing toolbox to operate photons
Quantum entanglement and quantum operation
Institute of Scientific and Technical Information of China (English)
无
2008-01-01
It is a simple introduction to quantum entanglement and quantum operations. The authors focus on some applications of quantum entanglement and relations between two-qubit entangled states and unitary operations. It includes remote state preparation by using any pure entangled states, nonlocal operation implementation using entangled states, entanglement capacity of two-qubit gates and two-qubit gates construction.
Nonlinear optics quantum computing with circuit QED.
Adhikari, Prabin; Hafezi, Mohammad; Taylor, J M
2013-02-08
One approach to quantum information processing is to use photons as quantum bits and rely on linear optical elements for most operations. However, some optical nonlinearity is necessary to enable universal quantum computing. Here, we suggest a circuit-QED approach to nonlinear optics quantum computing in the microwave regime, including a deterministic two-photon phase gate. Our specific example uses a hybrid quantum system comprising a LC resonator coupled to a superconducting flux qubit to implement a nonlinear coupling. Compared to the self-Kerr nonlinearity, we find that our approach has improved tolerance to noise in the qubit while maintaining fast operation.
Classical Ising model test for quantum circuits
Geraci, Joseph; Lidar, Daniel A.
2010-07-01
We exploit a recently constructed mapping between quantum circuits and graphs in order to prove that circuits corresponding to certain planar graphs can be efficiently simulated classically. The proof uses an expression for the Ising model partition function in terms of quadratically signed weight enumerators (QWGTs), which are polynomials that arise naturally in an expansion of quantum circuits in terms of rotations involving Pauli matrices. We combine this expression with a known efficient classical algorithm for the Ising partition function of any planar graph in the absence of an external magnetic field, and the Robertson-Seymour theorem from graph theory. We give as an example a set of quantum circuits with a small number of non-nearest-neighbor gates which admit an efficient classical simulation.
System-environment correlations for dephasing two-qubit states coupled to thermal baths
Costa, A. C. S.; Beims, M. W.; Strunz, W. T.
2016-05-01
Based on the exact dynamics of a two-qubit system and environment, we investigate system-environment (SE) quantum and classical correlations. The coupling is chosen to represent a dephasing channel for one of the qubits and the environment is a proper thermal bath. First we discuss the general issue of dilation for qubit phase damping. Based on the usual thermal bath of harmonic oscillators, we derive criteria of separability and entanglement between an initial X state and the environment. Applying these criteria to initial Werner states, we find that entanglement between the system and environment is built up in time for temperatures below a certain critical temperature Tcrit. On the other hand, the total state remains separable during those short times that are relevant for decoherence and loss of entanglement in the two-qubit state. Close to Tcrit the SE correlations oscillate between separable and entangled. Even though these oscillations are also observed in the entanglement between the two qubits, no simple relation between the loss of entanglement in the two-qubit system and the build-up of entanglement between the system and environment is found.
Noise gates for decoherent quantum circuits
Bassi, Angelo; Deckert, D. -A.
2008-01-01
A major problem in exploiting microscopic systems for developing a new technology based on the principles of Quantum Information is the influence of noise which tends to work against the quantum features of such systems. It becomes then crucial to understand how noise affects the evolution of quantum circuits: several techniques have been proposed among which stochastic differential equations (SDEs) can represent a very convenient tool. We show how SDEs naturally map any Markovian noise into ...
Multi-qubit circuit quantum electrodynamics
Energy Technology Data Exchange (ETDEWEB)
Viehmann, Oliver
2013-09-03
Circuit QED systems are macroscopic, man-made quantum systems in which superconducting artificial atoms, also called Josephson qubits, interact with a quantized electromagnetic field. These systems have been devised to mimic the physics of elementary quantum optical systems with real atoms in a scalable and more flexible framework. This opens up a variety of possible applications of circuit QED systems. For instance, they provide a promising platform for processing quantum information. Recent years have seen rapid experimental progress on these systems, and experiments with multi-component circuit QED architectures are currently starting to come within reach. In this thesis, circuit QED systems with multiple Josephson qubits are studied theoretically. We focus on simple and experimentally realistic extensions of the currently operated circuit QED setups and pursue investigations in two main directions. First, we consider the equilibrium behavior of circuit QED systems containing a large number of mutually noninteracting Josephson charge qubits. The currently accepted standard description of circuit QED predicts the possibility of superradiant phase transitions in such systems. However, a full microscopic treatment shows that a no-go theorem for superradiant phase transitions known from atomic physics applies to circuit QED systems as well. This reveals previously unknown limitations of the applicability of the standard theory of circuit QED to multi-qubit systems. Second, we explore the potential of circuit QED for quantum simulations of interacting quantum many-body systems. We propose and analyze a circuit QED architecture that implements the quantum Ising chain in a time-dependent transverse magnetic field. Our setup can be used to study quench dynamics, the propagation of localized excitations, and other non-equilibrium features in this paradigmatic model in the theory of non-equilibrium thermodynamics and quantumcritical phenomena. The setup is based on a
Numerical approach of the quantum circuit theory
Silva, J. J. B.; Duarte-Filho, G. C.; Almeida, F. A. G.
2017-03-01
In this paper we develop a numerical method based on the quantum circuit theory to approach the coherent electronic transport in a network of quantum dots connected with arbitrary topology. The algorithm was employed in a circuit formed by quantum dots connected each other in a shape of a linear chain (associations in series), and of a ring (associations in series, and in parallel). For both systems we compute two current observables: conductance and shot noise power. We find an excellent agreement between our numerical results and the ones found in the literature. Moreover, we analyze the algorithm efficiency for a chain of quantum dots, where the mean processing time exhibits a linear dependence with the number of quantum dots in the array.
Numerical approach of the quantum circuit theory
Energy Technology Data Exchange (ETDEWEB)
Silva, J.J.B., E-mail: jaedsonfisica@hotmail.com; Duarte-Filho, G.C.; Almeida, F.A.G.
2017-03-15
In this paper we develop a numerical method based on the quantum circuit theory to approach the coherent electronic transport in a network of quantum dots connected with arbitrary topology. The algorithm was employed in a circuit formed by quantum dots connected each other in a shape of a linear chain (associations in series), and of a ring (associations in series, and in parallel). For both systems we compute two current observables: conductance and shot noise power. We find an excellent agreement between our numerical results and the ones found in the literature. Moreover, we analyze the algorithm efficiency for a chain of quantum dots, where the mean processing time exhibits a linear dependence with the number of quantum dots in the array.
Entanglement Genesis by Ancilla-Based Parity Measurement in 2D Circuit QED
Saira, O.P.; Groen, J.P.; Cramer, J.; Meretska, M.; De Lange, G.; DiCarlo, L.
2014-01-01
We present an indirect two-qubit parity meter in planar circuit quantum electrodynamics, realized by discrete interaction with an ancilla and a subsequent projective ancilla measurement with a dedicated, dispersively coupled resonator. Quantum process tomography and successful entanglement by measur
Manipulating the sudden death of entanglement in two-qubit atomic systems
Energy Technology Data Exchange (ETDEWEB)
Hussain, Mahmood Irtiza; Tahira, Rabia; Ikram, Manzoor [COMSATS Institute of Information Technology, Islamabad (Pakistan)
2011-10-15
We investigate the entanglement dynamics of a general two-qubit system in a noisy environment presenting analytical descriptions of the time evolution of entanglement having some unitary operations after its evolution in dissipative environments. We show that quantum gates (unitary operators) and bath switching can change the subsequent dynamics of entanglement. For this purpose, we consider {sigma}{sub x} and bath switching operations that change the disentanglement time from finite to infinite.
Photonic Quantum Circuits with Time Delays
Pichler, Hannes
2015-01-01
We study the dynamics of photonic quantum circuits consisting of nodes coupled by quantum channels. We are interested in the regime where time delay in communication between the nodes is significant. This includes the problem of quantum feedback, where a quantum signal is fed back on a system with a time delay. We develop a matrix product state approach to solve the Quantum Stochastic Schr\\"odinger Equation with time delays, which accounts in an efficient way for the entanglement of nodes with the stream of emitted photons in the waveguide, and thus the non-Markovian character of the dynamics. We illustrate this approach with two paradigmatic quantum optical examples: two coherently driven distant atoms coupled to a photonic waveguide with a time delay, and a driven atom coupled to its own output field with a time delay as an instance of a quantum feedback problem.
Depth optimization for topological quantum circuits
AlFailakawi, Mohammad; Ahmad, Imtiaz; AlTerkawi, Laila; Hamdan, Suha
2015-02-01
Topological quantum computing (TQC) model is one of the most promising models for quantum computation. A circuit implemented under TQC is optimized by reducing its depth due to special construction requirements in such technology. In this work, we propose a hybrid approach that combines a left-edge greedy heuristic with genetic algorithm (GA) to minimize circuit depth through combined line and gate ordering. In our implementation, GA is used to find line ordering, whereas the left edge is used to reduce circuit depth by taking into consideration overlap constraints imposed by line ordering. Moreover, the proposed algorithm can merge gates together realizing circuit with multi-target gates to provide reduced circuit depth. Experimental results on random benchmark circuits show that the proposed algorithm was able to reduce circuit depth by 42 % on average for CNOT circuits, with additional 5 % savings when multi-target optimization is used. Results on RevLib benchmarks revealed a typical enhancement of 21 % and an additional 11 % when multi-target gates are allowed.
Quantum Electric Circuits Analogous to Ballistic Conductors
2007-01-01
The conductance steps in a constricted two-dimensional electron gas and the minimum conductivity in graphene are related to a new uncertainty relation between electric charge and conductance in a quantized electric circuit that mimics the electric transport in mesoscopic systems. This uncertainty relation makes specific use of the discreteness of electric charge. Quantum electric circuits analogous to both constricted two-dimensional electron gas and graphene are introduced. In the latter cas...
Sequent Calculus Representations for Quantum Circuits
Directory of Open Access Journals (Sweden)
Cameron Beebe
2016-06-01
Full Text Available When considering a sequent-style proof system for quantum programs, there are certain elements of quantum mechanics that we may wish to capture, such as phase, dynamics of unitary transformations, and measurement probabilities. Traditional quantum logics which focus primarily on the abstract orthomodular lattice theory and structures of Hilbert spaces have not satisfactorily captured some of these elements. We can start from 'scratch' in an attempt to conceptually characterize the types of proof rules which should be in a system that represents elements necessary for quantum algorithms. This present work attempts to do this from the perspective of the quantum circuit model of quantum computation. A sequent calculus based on single quantum circuits is suggested, and its ability to incorporate important conceptual and dynamic aspects of quantum computing is discussed. In particular, preserving the representation of phase helps illustrate the role of interference as a resource in quantum computation. Interference also provides an intuitive basis for a non-monotonic calculus.
Computational quantum-classical boundary of noisy commuting quantum circuits.
Fujii, Keisuke; Tamate, Shuhei
2016-05-18
It is often said that the transition from quantum to classical worlds is caused by decoherence originated from an interaction between a system of interest and its surrounding environment. Here we establish a computational quantum-classical boundary from the viewpoint of classical simulatability of a quantum system under decoherence. Specifically, we consider commuting quantum circuits being subject to decoherence. Or equivalently, we can regard them as measurement-based quantum computation on decohered weighted graph states. To show intractability of classical simulation in the quantum side, we utilize the postselection argument and crucially strengthen it by taking noise effect into account. Classical simulatability in the classical side is also shown constructively by using both separable criteria in a projected-entangled-pair-state picture and the Gottesman-Knill theorem for mixed state Clifford circuits. We found that when each qubit is subject to a single-qubit complete-positive-trace-preserving noise, the computational quantum-classical boundary is sharply given by the noise rate required for the distillability of a magic state. The obtained quantum-classical boundary of noisy quantum dynamics reveals a complexity landscape of controlled quantum systems. This paves a way to an experimentally feasible verification of quantum mechanics in a high complexity limit beyond classically simulatable region.
Thermal rectification in nonlinear quantum circuits
DEFF Research Database (Denmark)
Ruokola, T.; Ojanen, T.; Jauho, Antti-Pekka
2009-01-01
We present a theoretical study of radiative heat transport in nonlinear solid-state quantum circuits. We give a detailed account of heat rectification effects, i.e., the asymmetry of heat current with respect to a reversal of the thermal gradient, in a system consisting of two reservoirs at finite...
Minimal resonator loss for circuit quantum electrodynamics
Barends, R.; Vercruyssen, N.; Endo, A.; De Visser, P.J.; Zijlstra, T.; Klapwijk, T.M.; Diener, P.; Yates, S.J.C.; Baselmans, J.J.A.
2010-01-01
We report quality factors of up to 500x10³ in superconducting resonators at the single photon levels needed for circuit quantum electrodynamics. This result is achieved by using NbTiN and removing the dielectric from regions with high electric fields. As demonstrated by a comparison with Ta, the cru
Efficient quantum walk on a quantum processor
Qiang, Xiaogang; Loke, Thomas; Montanaro, Ashley; Aungskunsiri, Kanin; Zhou, Xiaoqi; O'Brien, Jeremy L.; Wang, Jingbo B.; Matthews, Jonathan C. F.
2016-05-01
The random walk formalism is used across a wide range of applications, from modelling share prices to predicting population genetics. Likewise, quantum walks have shown much potential as a framework for developing new quantum algorithms. Here we present explicit efficient quantum circuits for implementing continuous-time quantum walks on the circulant class of graphs. These circuits allow us to sample from the output probability distributions of quantum walks on circulant graphs efficiently. We also show that solving the same sampling problem for arbitrary circulant quantum circuits is intractable for a classical computer, assuming conjectures from computational complexity theory. This is a new link between continuous-time quantum walks and computational complexity theory and it indicates a family of tasks that could ultimately demonstrate quantum supremacy over classical computers. As a proof of principle, we experimentally implement the proposed quantum circuit on an example circulant graph using a two-qubit photonics quantum processor.
Efficient quantum walk on a quantum processor.
Qiang, Xiaogang; Loke, Thomas; Montanaro, Ashley; Aungskunsiri, Kanin; Zhou, Xiaoqi; O'Brien, Jeremy L; Wang, Jingbo B; Matthews, Jonathan C F
2016-05-05
The random walk formalism is used across a wide range of applications, from modelling share prices to predicting population genetics. Likewise, quantum walks have shown much potential as a framework for developing new quantum algorithms. Here we present explicit efficient quantum circuits for implementing continuous-time quantum walks on the circulant class of graphs. These circuits allow us to sample from the output probability distributions of quantum walks on circulant graphs efficiently. We also show that solving the same sampling problem for arbitrary circulant quantum circuits is intractable for a classical computer, assuming conjectures from computational complexity theory. This is a new link between continuous-time quantum walks and computational complexity theory and it indicates a family of tasks that could ultimately demonstrate quantum supremacy over classical computers. As a proof of principle, we experimentally implement the proposed quantum circuit on an example circulant graph using a two-qubit photonics quantum processor.
One-Way Information Deficit and Geometry for a Class of Two-Qubit States
Institute of Scientific and Technical Information of China (English)
WANG Yao-Kun; MA Teng; LI Bo; WANG Zhi-Xi
2013-01-01
The work deficit,as introduced by Jonathan Oppenheim et al.[Phys.Rev.Lett.89 (2002) 180402]is a good measure of the quantum correlations in a state and provides a new standpoint for understanding quantum non-locality.In this paper,we analytically evaluate the one-way information deficit (OWID) for the Bell-diagonal states and a class of two-qubit states and further give the geometry picture for OWID.The dynamic behavior of the OWID under decoherence channel is investigated and it is shown that the OWID of some classes of X states is more robust against the decoherence than the entanglement.
Effects of Noise on Joint Remote State Preparation of an Arbitrary Equatorial Two-Qubit State
Zhao, Hong-xia; Huang, Li
2017-03-01
By using a six-qubit cluster state as the quantum channel, we investigat the joint remote state preparation of an arbitrary equatorial two-qubit state. We analytically obtain the fidelities of the joint remote state preparation process in noisy environments, such as the amplitude-damping noise and phase-damping noise. In our scheme, the two different noise including amplitude-damping noise and the phase-damping noise only affect the travel qubits of the quantum channel, and then we show that the fidelities in these two noisy cases only depend on the decoherence noisy rate.
Deterministic Joint Remote Preparation of an Arbitrary Two-Qubit State Using the Cluster State
Institute of Scientific and Technical Information of China (English)
WANG Ming-Ming; CHEN Xiu-Bo; YANG Yi-Xian
2013-01-01
Recently,deterministic joint remote state preparation (JRSP) schemes have been proposed to achieve 100％ success probability.In this paper,we propose a new version of deterministic JRSP scheme of an arbitrary two-qubit state by using the six-qubit cluster state as shared quantum resource.Compared with previous schemes,our scheme has high efficiency since less quantum resource is required,some additional unitary operations and measurements are unnecessary.We point out that the existing two types of deterministic JRSP schemes based on GHZ states and EPR pairs are equivalent.
Remote two-qubit state creation and its robustness
Stolze, J.; Zenchuk, A. I.
2016-08-01
We consider the problem of remote two-qubit state creation using the two-qubit excitation pure initial state of the sender. The communication line is based on the optimized boundary-controlled chain with two pairs of properly adjusted coupling constants. We show that the communication line can be characterized by a set of parameters independent of the initial state of the sender. These parameters are permanent attributes of a communication line and can be either calculated theoretically or measured in experiment. In particular, they determine the creatable subregion of the receiver's state space. The creation of a particular state within the creatable region is achieved by a proper choice of the independent parameters of the sender's initial state (control parameters) and reduces to the solvability of a certain system of algebraic equations. The creation of the two-qubit Werner state is considered as an example. We also study the effects of imperfections of the chain on the state creation.
Entangled Bloch spheres: Bloch matrix and two-qubit state space
Gamel, Omar
2016-06-01
We represent a two-qubit density matrix in the basis of Pauli matrix tensor products, with the coefficients constituting a Bloch matrix, analogous to the single qubit Bloch vector. We find the quantum state positivity requirements on the Bloch matrix components, leading to three important inequalities, allowing us to parametrize and visualize the two-qubit state space. Applying the singular value decomposition naturally separates the degrees of freedom to local and nonlocal, and simplifies the positivity inequalities. It also allows us to geometrically represent a state as two entangled Bloch spheres with superimposed correlation axes. It is shown that unitary transformations, local or nonlocal, have simple interpretations as axis rotations or mixing of certain degrees of freedom. The nonlocal unitary invariants of the state are then derived in terms of local unitary invariants. The positive partial transpose criterion for entanglement is generalized, and interpreted as a reflection, or a change of a single sign. The formalism is used to characterize maximally entangled states, and generalize two qubit isotropic and Werner states.
Macroscopic Quantum Criticality in a Circuit QED
Wang, Y D; Nori, F; Quan, H T; Sun, C P; Liu, Yu-xi; Nori, Franco
2006-01-01
Cavity quantum electrodynamic (QED) is studied for two strongly-coupled charge qubits interacting with a single-mode quantized field, which is provided by a on-chip transmission line resonator. We analyze the dressed state structure of this superconducting circuit QED system and the selection rules of electromagnetic-induced transitions between any two of these dressed states. Its macroscopic quantum criticality, in the form of ground state level crossing, is also analyzed, resulting from competition between the Ising-type inter-qubit coupling and the controllable on-site potentials.
Quantum memory with millisecond coherence in circuit QED
Reagor, Matthew; Pfaff, Wolfgang; Axline, Christopher; Heeres, Reinier W.; Ofek, Nissim; Sliwa, Katrina; Holland, Eric; Wang, Chen; Blumoff, Jacob; Chou, Kevin; Hatridge, Michael J.; Frunzio, Luigi; Devoret, Michel H.; Jiang, Liang; Schoelkopf, Robert J.
2016-07-01
Significant advances in coherence render superconducting quantum circuits a viable platform for fault-tolerant quantum computing. To further extend capabilities, highly coherent quantum systems could act as quantum memories for these circuits. A useful quantum memory must be rapidly addressable by Josephson-junction-based artificial atoms, while maintaining superior coherence. We demonstrate a superconducting microwave cavity architecture that is highly robust against major sources of loss that are encountered in the engineering of circuit QED systems. The architecture allows for storage of quantum superpositions in a resonator on the millisecond scale, while strong coupling between the resonator and a transmon qubit enables control, encoding, and readout at MHz rates. This extends the maximum available coherence time attainable in superconducting circuits by almost an order of magnitude compared to earlier hardware. Our design is an ideal platform for studying coherent quantum optics and marks an important step towards hardware-efficient quantum computing in Josephson-junction-based quantum circuits.
Yabu-uti, Bruno F C
2011-01-01
We propose an alternative scheme to implement a two-qubits Controlled-U gate in the hybrid system atom-$CCA$ (coupled cavities array). Our scheme results in a constant gating time and, with an adjustable qubit-bus coupling (atom-resonator), one can specify a particular transformation $U$ on the target qubit. We believe that this proposal may open promising perspectives for networking quantum information processors and implementing distributed and scalable quantum computation.
Effect of noise on deterministic joint remote preparation of an arbitrary two-qubit state
Wang, Ming-Ming; Qu, Zhi-Guo; Wang, Wei; Chen, Jin-Guang
2017-05-01
Quantum communication has attracted much attention in recent years. Deterministic joint remote state preparation (DJRSP) is an important branch of quantum secure communication which could securely transmit a quantum state with 100% success probability. In this paper, we study DJRSP of an arbitrary two-qubit state in noisy environment. Taking a GHZ based DJRSP scheme of a two-qubit state as an example, we study how the scheme is influenced by all types of noise usually encountered in real-world implementations of quantum communication protocols, i.e., the bit-flip, phase-flip (phase-damping), depolarizing, and amplitude-damping noise. We demonstrate that there are four different output states in the amplitude-damping noise, while there is the same output state in each of the other three types of noise. The state-independent average fidelity is presented to measure the effect of noise, and it is shown that the depolarizing noise has the worst effect on the DJRSP scheme, while the amplitude-damping noise or the phase-flip has the slightest effect depending on the noise rate. Our results are also suitable for JRSP and RSP.
On Multiplicative Linear Logic, Modality and Quantum Circuits
Directory of Open Access Journals (Sweden)
Ugo Dal Lago
2012-10-01
Full Text Available A logical system derived from linear logic and called QMLL is introduced and shown able to capture all unitary quantum circuits. Conversely, any proof is shown to compute, through a concrete GoI interpretation, some quantum circuits. The system QMLL, which enjoys cut-elimination, is obtained by endowing multiplicative linear logic with a quantum modality.
Institute of Scientific and Technical Information of China (English)
XU Hai-Feng; HAN Lian-Fang
2013-01-01
We propose a tripartite scheme for probabilistically teleporting an arbitrary two-qubit state with a fourqubit duster-class state and a Bell-class state as the quantum channels.In the scheme,the sender and the controller make Bell-state measurements (BSMs) on their respective qubit pairs.With their measurement results,the receiver can reconstruct the original state probabilistically by introducing two auxiliary particles and making appropriate unitary operations and positive operator-valued measure (POVM) instead of usual projective measurement.Moreover,the total success probability and classical communication cost of the present protocol are also worked out.
A method of extracting operating parameters of a quantum circuit
Sete, Eyob A.; Block, Maxwell; Scheer, Michael; Zanoci, Cris; Vahidpour, Mehrnoosh; Thompson, Dane; Rigetti, Chad
Rigorous simulation-driven design methods are an essential component of traditional integrated circuit design. We adapt these techniques to the design and development of superconducting quantum integrated circuits by combining classical finite element analysis in the microwave domain with Brune circuit synthesis by Solgun [PhD thesis 2014] and BKD Hamiltonian analysis by Burkard et al. [Phys. Rev. B 69, 064503 (2004)]. Using the Hamiltonian of the quantum circuit, constructed using the synthesized equivalent linear circuit and the nonlinear Josephson junctions' contributions, we extract operating parameters of the quantum circuit such as resonance coupling strength, dispersive shift, qubit anharmonicitiy, and decoherence rates for single-and multi-port quantum circuits. This approach has been experimentally validated and allows the closed-loop iterative simulation-driven development of quantum information processing devices.
Commuting quantum circuits: efficient classical simulations versus hardness results
Ni, Xiaotong
2012-01-01
The study of quantum circuits composed of commuting gates is particularly useful to understand the delicate boundary between quantum and classical computation. Indeed, while being a restricted class, commuting circuits exhibit genuine quantum effects such as entanglement. In this paper we show that the computational power of commuting circuits exhibits a surprisingly rich structure. First we show that every 2-local commuting circuit acting on d-level systems and followed by single-qudit measurements can be efficiently simulated classically with high accuracy. In contrast, we prove that such strong simulations are hard for 3-local circuits. Using sampling methods we further show that all commuting circuits composed of exponentiated Pauli operators e^{i\\theta P} can be simulated efficiently classically when followed by single-qubit measurements. Finally, we show that commuting circuits can efficiently simulate certain non-commutative processes, related in particular to constant-depth quantum circuits. This give...
Energy Technology Data Exchange (ETDEWEB)
Yabu-uti, B.F.C., E-mail: yabuuti@ifi.unicamp.br [Instituto de Fisica ' Gleb Wataghin' , Universidade Estadual de Campinas, 13083-970 Campinas, SP (Brazil); Roversi, J.A., E-mail: roversi@ifi.unicamp.br [Instituto de Fisica ' Gleb Wataghin' , Universidade Estadual de Campinas, 13083-970 Campinas, SP (Brazil)
2011-08-22
We propose an alternative scheme to implement a two-qubit controlled-R (rotation) gate in the hybrid atom-CCA (coupled cavities array) system. Our scheme results in a constant gating time and, with an adjustable qubit-bus coupling (atom-resonator), one can specify a particular rotation R on the target qubit. We believe that this proposal may open promising perspectives for networking quantum information processors and implementing distributed and scalable quantum computation. -- Highlights: → We propose an alternative two-qubit controlled-rotation gate implementation. → Our gate is realized in a constant gating time for any rotation. → A particular rotation on the target qubit can be specified by an adjustable qubit-bus coupling. → Our proposal may open promising perspectives for implementing distributed and scalable quantum computation.
Entropy Flow in Near-Critical Quantum Circuits
Friedan, Daniel
2017-05-01
Near-critical quantum circuits close to equilibrium are ideal physical systems for asymptotically large-scale quantum computers, because their low energy collective excitations evolve reversibly, effectively isolated from microscopic environmental fluctuations by the renormalization group. Entropy flows in near-critical quantum circuits near equilibrium as a locally conserved quantum current, obeying circuit laws analogous to the electric circuit laws. These "Kirchhoff laws" for entropy flow are the fundamental design constraints for asymptotically large-scale quantum computers. A quantum circuit made from a near-critical system (of conventional type) is described by a relativistic 1+1 dimensional relativistic quantum field theory on the circuit. The quantum entropy current near equilibrium is just the energy current divided by the temperature. The universal properties of the energy-momentum tensor constrain the entropy flow characteristics of the circuit components: the entropic conductivity of the quantum wires and the entropic admittance of the quantum circuit junctions. For example, near-critical quantum wires are always resistanceless inductors for entropy. A universal formula is derived for the entropic conductivity: σ S(ω ) = iv2 S/ω T , where ω is the frequency, T the temperature, S the equilibrium entropy density and v the velocity of "light". The thermal conductivity is Re(Tσ S(ω ))=π v2 S δ (ω ). The thermal Drude weight is, universally, v2S. This gives a way to measure the entropy density directly.
Hybrid quantum circuit with implanted erbium ions
Energy Technology Data Exchange (ETDEWEB)
Probst, S.; Rotzinger, H.; Tkalčec, A. [Physikalisches Institut, Karlsruhe Institute of Technology, D-76128 Karlsruhe (Germany); Kukharchyk, N.; Wieck, A. D. [Angewandte Festkörperphysik, Ruhr-Universität Bochum, Universitätsstraße 150, D-44780 Bochum (Germany); Wünsch, S.; Siegel, M. [Institut für Mikro- und Nanoelektronische Systeme, Karlsruhe Institute of Technology, D-76189 Karlsruhe (Germany); Ustinov, A. V. [Physikalisches Institut, Karlsruhe Institute of Technology, D-76128 Karlsruhe (Germany); Laboratory of Superconducting Metamaterials, National University of Science and Technology “MISIS,” Moscow 119049 (Russian Federation); Bushev, P. A. [Experimentalphysik, Universität des Saarlandes, D-66123 Saarbrücken (Germany)
2014-10-20
We report on hybrid circuit quantum electrodynamics experiments with focused ion beam implanted Er{sup 3+} ions in Y{sub 2}SiO{sub 5} coupled to an array of superconducting lumped element microwave resonators. The Y{sub 2}SiO{sub 5} crystal is divided into several areas with distinct erbium doping concentrations, each coupled to a separate resonator. The coupling strength is varied from 5 MHz to 18.7 MHz, while the linewidth ranges between 50 MHz and 130 MHz. We confirm the paramagnetic properties of the implanted spin ensemble by evaluating the temperature dependence of the coupling. The efficiency of the implantation process is analyzed and the results are compared to a bulk doped Er:Y{sub 2}SiO{sub 5} sample. We demonstrate the integration of these engineered erbium spin ensembles with superconducting circuits.
Superconducting circuits for quantum information: an outlook.
Devoret, M H; Schoelkopf, R J
2013-03-08
The performance of superconducting qubits has improved by several orders of magnitude in the past decade. These circuits benefit from the robustness of superconductivity and the Josephson effect, and at present they have not encountered any hard physical limits. However, building an error-corrected information processor with many such qubits will require solving specific architecture problems that constitute a new field of research. For the first time, physicists will have to master quantum error correction to design and operate complex active systems that are dissipative in nature, yet remain coherent indefinitely. We offer a view on some directions for the field and speculate on its future.
Quantum Effects of Mesoscopic Inductance and Capacity Coupling Circuits
Institute of Scientific and Technical Information of China (English)
LIU Jian-Xin; AN Zhan-Yuan; SONG Yong-Hua
2006-01-01
Using the quantum theory for a mesoscopic circuit based on the discretenes of electric charges, the finitedifference Schrodinger equation of the non-dissipative mesoscopic inductance and capacity coupling circuit is achieved.The Coulomb blockade effect, which is caused by the discreteness of electric charges, is studied. Appropriately choose the components in the circuits, the finite-difference Schrodinger equation can be divided into two Mathieu equations in p representation. With the WKBJ method, the currents quantum fluctuations in the ground states of the two circuits are calculated. The results show that the currents quantum zero-point fluctuations of the two circuits are exist and correlated.
Quantum Teleportation circuit using Matlab and Mathematica
Directory of Open Access Journals (Sweden)
Ms.Swati Sharma,
2010-08-01
Full Text Available This Paper describes a basic Quantum Teleportation circuit using mat lab Qlib tool. Teleportation is a new and exciting field of future communication. We know that security in data communication is a major concern nowadays. Among the encryption technologies that are available at present, shared key is the most reliable which depends on secure key generation and distribution. Teleportation/ ntanglement is a perfect solution for secure key generation and distribution, as for the no cloning theorem of quantum mechanics any attempt to intercept the key by the eavesdropper will be detectable immediately. A program is simulated with successful simulation which give successful transfer of random qubit to output and which governs perfect communication between Alice and Bob.
Universal programmable quantum circuit schemes to emulate an operator.
Daskin, Anmer; Grama, Ananth; Kollias, Giorgos; Kais, Sabre
2012-12-21
Unlike fixed designs, programmable circuit designs support an infinite number of operators. The functionality of a programmable circuit can be altered by simply changing the angle values of the rotation gates in the circuit. Here, we present a new quantum circuit design technique resulting in two general programmable circuit schemes. The circuit schemes can be used to simulate any given operator by setting the angle values in the circuit. This provides a fixed circuit design whose angles are determined from the elements of the given matrix-which can be non-unitary-in an efficient way. We also give both the classical and quantum complexity analysis for these circuits and show that the circuits require a few classical computations. For the electronic structure simulation on a quantum computer, one has to perform the following steps: prepare the initial wave function of the system; present the evolution operator U = e(-iHt) for a given atomic and molecular Hamiltonian H in terms of quantum gates array and apply the phase estimation algorithm to find the energy eigenvalues. Thus, in the circuit model of quantum computing for quantum chemistry, a crucial step is presenting the evolution operator for the atomic and molecular Hamiltonians in terms of quantum gate arrays. Since the presented circuit designs are independent from the matrix decomposition techniques and the global optimization processes used to find quantum circuits for a given operator, high accuracy simulations can be done for the unitary propagators of molecular Hamiltonians on quantum computers. As an example, we show how to build the circuit design for the hydrogen molecule.
Systematically Generated Two-Qubit Braids for Fibonacci Anyons
Zeuch, Daniel; Carnahan, Caitlin; Bonesteel, N. E.
We show how two-qubit Fibonacci anyon braids can be generated using a simple iterative procedure which, in contrast to previous methods, does not require brute force search. Our construction is closely related to that of, but with the new feature that it can be used for three-anyon qubits as well as four-anyon qubits. The iterative procedure we use, which was introduced by Reichardt, generates sequences of three-anyon weaves that asymptotically conserve the total charge of two of the three anyons, without control over the corresponding phase factors. The resulting two-qubit gates are independent of these factors and their length grows as log 1/ ɛ, where ɛ is the error, which is asymptotically better than the Solovay-Kitaev method.
An efficient quantum circuit analyser on qubits and qudits
Loke, T.; Wang, J. B.
2011-10-01
This paper presents a highly efficient decomposition scheme and its associated Mathematica notebook for the analysis of complicated quantum circuits comprised of single/multiple qubit and qudit quantum gates. In particular, this scheme reduces the evaluation of multiple unitary gate operations with many conditionals to just two matrix additions, regardless of the number of conditionals or gate dimensions. This improves significantly the capability of a quantum circuit analyser implemented in a classical computer. This is also the first efficient quantum circuit analyser to include qudit quantum logic gates.
Quantum memristor in a superconducting circuit
Salmilehto, Juha; Sanz, Mikel; di Ventra, Massimiliano; Solano, Enrique
Memristors, resistive elements that retain information of their past, have garnered interest due to their paradigm-changing potential in information processing and electronics. The emergent hysteretic behaviour allows for novel architectural applications and has recently been classically demonstrated in a simplified superconducting setup using the phase-dependent conductance in the tunnel-junction-microscopic model. In this contribution, we present a truly quantum model for a memristor constructed using established elements and techniques in superconducting nanoelectronics, and explore the parameters for feasible operation as well as refine the methods for quantifying the memory retention. In particular, the memristive behaviour is shown to arise from quasiparticle-induced tunneling in the full dissipative model and can be observed in the phase-driven tunneling current. The relevant hysteretic behaviour should be observable using current state-of-the-art measurements for detecting quasiparticle excitations. Our theoretical findings constitute the first quantum memristor in a superconducting circuit and act as the starting point for designing further circuit elements that have non-Markovian characteristics The authors acknowledge support from the CCQED EU project and the Finnish Cultural Foundation.
A Quantum Algorithm for Finding a Hamilton Circuit
Institute of Scientific and Technical Information of China (English)
GUO Hao; LONG Gui-Lu; SUN Yang; XIU Xiao-Lin
2001-01-01
A quantum algorithm for solving the classical NP-complete problem - the Hamilton circuit is presented. The algorithm employs the quantum SAT and the quantum search algorithms. The algorithm is square-root faster than classical algorithm, and becomes exponentially faster than classical algorithm if nonlinear quantum mechanical computer is used.
On the Quantum Circuit Complexity Equivalence
Drezgic, M; Drezgic, Milos; Sastry, Shankar
2007-01-01
Nielsen \\cite{Nielsen05} recently asked the following question: "What is the minimal size quantum circuit required to exactly implement a specified $% \\mathit{n}$-qubit unitary operation $U$, without the use of ancilla qubits?" Nielsen was able to prove that a lower bound on the minimal size circuit is provided by the length of the geodesic between the identity $I$ and $U$, where the length is defined by a suitable Finsler metric on $SU(2^{n})$. We prove that the minimum circuit size that simulates $U$ is in linear relation with the geodesic length and simulation parameters, for the given Finsler structure $F$. As a corollary we prove the highest lower bound of $O(\\frac{% n^{4}}{p}d_{F_{p}}^{2}(I,U)L_{F_{p}}(I,\\tilde{U})) $and the lowest upper bound of $\\Omega (n^{4}d_{F_{p}}^{3}(I,U))$, for the standard simulation technique. Therefore, our results show that by standard simulation one can not expect a better then $n^{2}$ times improvement in the upper bound over the result from Nielsen, Dowling, Gu and Dohert...
Quantum networks with chiral light--matter interaction in waveguides
Mahmoodian, Sahand; Sørensen, Anders S
2016-01-01
We design and analyze a simple on-chip photonic circuit that can form a universal building block of a quantum network. The circuit consists of a single-photon source, and two quantum emitters positioned in two arms of an on-chip Mach-Zehnder interferometer composed of waveguides with chiral light--matter interfaces. The efficient chiral light--matter interaction allows the emitters to act as photon sources to herald internode entanglement, and to perform high-fidelity intranode two-qubit gates within a single chip without any need for reconfiguration. We show that by connecting multiple circuits of this kind into a quantum network, it is possible to perform universal quantum computation with heralded two-qubit gate fidelities ${\\cal F} \\sim 0.998$ achievable in state-of-the-art quantum dot systems.
Asymptotically Optimal Quantum Circuits for d-level Systems
Bullock, S S; O'Leary, D P; Brennen, Gavin K.; Bullock, Stephen S.; Leary, Dianne P. O'
2004-01-01
As a qubit is a two-level quantum system whose state space is spanned by |0>, |1>, so a qudit is a d-level quantum system whose state space is spanned by |0>,...,|d-1>. Quantum computation has stimulated much recent interest in algorithms factoring unitary evolutions of an n-qubit state space into component two-particle unitary evolutions. In the absence of symmetry, Shende, Markov and Bullock use Sard's theorem to prove that at least C 4^n two-qubit unitary evolutions are required, while Vartiainen, Moettoenen, and Salomaa (VMS) use the QR matrix factorization and Gray codes in an optimal order construction involving two-particle evolutions. In this work, we note that Sard's theorem demands C d^{2n} two-qudit unitary evolutions to construct a generic (symmetry-less) n-qudit evolution. However, the VMS result applied to virtual-qubits only recovers optimal order in the case that d is a power of two. We further construct a QR decomposition for d-multi-level quantum logics, proving a sharp asymptotic of Theta(d...
Singh, Manu Pratap; Rajput, Balwant S.
2017-04-01
New set of maximally entangled states (Singh-Rajput MES), constituting orthonormal eigen bases, has been revisited and its superiority and suitability in pattern-association (Quantum Associative Memory, QuAM) have been demonstrated. Using these MES as memory states in the evolutionary process of pattern storage in a two-qubit system, it has been shown that the first two states of Singh-Rajput MES are useful for storing the pattern |11> and the last two of these MES are useful in storing the pattern |10> Recall operations of quantum associate memory (QuAM) have been conducted through evolutionary process in terms of unitary operators by separately choosing Singh-Rajput MES and Bell's MES as memory states and it has been shown that Singh-Rajput MES as valid memory states for recalling the patterns in a two-qubit system are much more suitable than Bell's MES.
Quantum entanglement and quantum operation
Institute of Scientific and Technical Information of China (English)
2008-01-01
It is a simple introduction to quantum entanglement and quantum operations.The authors focus on some applications of quantum entanglement and relations between two-qubit entangled states and unitary operations.It includes remote state preparation by using any pure entangled states,nonlocal operation implementation using entangled states,entanglement capacity of two-qubit gates and two-qubit gates construction.
Novel Quaternary Quantum Decoder, Multiplexer and Demultiplexer Circuits
Haghparast, Majid; Monfared, Asma Taheri
2017-05-01
Multiple valued logic is a promising approach to reduce the width of the reversible or quantum circuits, moreover, quaternary logic is considered as being a good choice for future quantum computing technology hence it is very suitable for the encoded realization of binary logic functions through its grouping of 2-bits together into quaternary values. The Quaternary decoder, multiplexer, and demultiplexer are essential units of quaternary digital systems. In this paper, we have initially designed a quantum realization of the quaternary decoder circuit using quaternary 1-qudit gates and quaternary Muthukrishnan-Stroud gates. Then we have presented quantum realization of quaternary multiplexer and demultiplexer circuits using the constructed quaternary decoder circuit and quaternary controlled Feynman gates. The suggested circuits in this paper have a lower quantum cost and hardware complexity than the existing designs that are currently used in quaternary digital systems. All the scales applied in this paper are based on Nanometric area.
Novel Quaternary Quantum Decoder, Multiplexer and Demultiplexer Circuits
Haghparast, Majid; Monfared, Asma Taheri
2017-02-01
Multiple valued logic is a promising approach to reduce the width of the reversible or quantum circuits, moreover, quaternary logic is considered as being a good choice for future quantum computing technology hence it is very suitable for the encoded realization of binary logic functions through its grouping of 2-bits together into quaternary values. The Quaternary decoder, multiplexer, and demultiplexer are essential units of quaternary digital systems. In this paper, we have initially designed a quantum realization of the quaternary decoder circuit using quaternary 1-qudit gates and quaternary Muthukrishnan-Stroud gates. Then we have presented quantum realization of quaternary multiplexer and demultiplexer circuits using the constructed quaternary decoder circuit and quaternary controlled Feynman gates. The suggested circuits in this paper have a lower quantum cost and hardware complexity than the existing designs that are currently used in quaternary digital systems. All the scales applied in this paper are based on Nanometric area.
Quantum game simulator, using the circuit model of quantum computation
Vlachos, Panagiotis; Karafyllidis, Ioannis G.
2009-10-01
We present a general two-player quantum game simulator that can simulate any two-player quantum game described by a 2×2 payoff matrix (two strategy games).The user can determine the payoff matrices for both players, their strategies and the amount of entanglement between their initial strategies. The outputs of the simulator are the expected payoffs of each player as a function of the other player's strategy parameters and the amount of entanglement. The simulator also produces contour plots that divide the strategy spaces of the game in regions in which players can get larger payoffs if they choose to use a quantum strategy against any classical one. We also apply the simulator to two well-known quantum games, the Battle of Sexes and the Chicken game. Program summaryProgram title: Quantum Game Simulator (QGS) Catalogue identifier: AEED_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEED_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 3416 No. of bytes in distributed program, including test data, etc.: 583 553 Distribution format: tar.gz Programming language: Matlab R2008a (C) Computer: Any computer that can sufficiently run Matlab R2008a Operating system: Any system that can sufficiently run Matlab R2008a Classification: 4.15 Nature of problem: Simulation of two player quantum games described by a payoff matrix. Solution method: The program calculates the matrices that comprise the Eisert setup for quantum games based on the quantum circuit model. There are 5 parameters that can be altered. We define 3 of them as constant. We play the quantum game for all possible values for the other 2 parameters and store the results in a matrix. Unusual features: The software provides an easy way of simulating any two-player quantum games. Running time: Approximately
Quantum Circuit Synthesis using a New Quantum Logic Gate Library of NCV Quantum Gates
Li, Zhiqiang; Chen, Sai; Song, Xiaoyu; Perkowski, Marek; Chen, Hanwu; Zhu, Wei
2017-04-01
Since Controlled-Square-Root-of-NOT (CV, CV‡) gates are not permutative quantum gates, many existing methods cannot effectively synthesize optimal 3-qubit circuits directly using the NOT, CNOT, Controlled-Square-Root-of-NOT quantum gate library (NCV), and the key of effective methods is the mapping of NCV gates to four-valued quantum gates. Firstly, we use NCV gates to create the new quantum logic gate library, which can be directly used to get the solutions with smaller quantum costs efficiently. Further, we present a novel generic method which quickly and directly constructs this new optimal quantum logic gate library using CNOT and Controlled-Square-Root-of-NOT gates. Finally, we present several encouraging experiments using these new permutative gates, and give a careful analysis of the method, which introduces a new idea to quantum circuit synthesis.
Quantum Circuit Synthesis using a New Quantum Logic Gate Library of NCV Quantum Gates
Li, Zhiqiang; Chen, Sai; Song, Xiaoyu; Perkowski, Marek; Chen, Hanwu; Zhu, Wei
2016-12-01
Since Controlled-Square-Root-of-NOT (CV, CV‡) gates are not permutative quantum gates, many existing methods cannot effectively synthesize optimal 3-qubit circuits directly using the NOT, CNOT, Controlled-Square-Root-of-NOT quantum gate library (NCV), and the key of effective methods is the mapping of NCV gates to four-valued quantum gates. Firstly, we use NCV gates to create the new quantum logic gate library, which can be directly used to get the solutions with smaller quantum costs efficiently. Further, we present a novel generic method which quickly and directly constructs this new optimal quantum logic gate library using CNOT and Controlled-Square-Root-of-NOT gates. Finally, we present several encouraging experiments using these new permutative gates, and give a careful analysis of the method, which introduces a new idea to quantum circuit synthesis.
Quantum Circuits Fanout, Parity and Counting
Moore, Cristopher
1999-01-01
We propose definitions of QAC^0, the quantum analog of the classical class AC^0 of constant-depth circuits with AND and OR gates of arbitrary fan-in, and QACC^0[q], where n-ary Mod-q gates are also allowed. We show that it is possible to make a `cat' state on n qubits in constant depth if and only if we can construct a parity or Mod-2 gate in constant depth; therefore, any circuit class that can fan out a qubit to n copies in constant depth also includes QACC^0[2]. In addition, we prove the somewhat surprising result that parity or fanout allows us to construct Mod-q gates in constant depth for any q, so QACC^0[2] = QACC^0. Since ACC^0[p] != ACC^0[q] whenever p and q are mutually prime, QACC^0[2] is strictly more powerful than its classical counterpart, as is QAC^0 when fanout is allowed.
Manipulating the quantum state of an electrical circuit.
Vion, D; Aassime, A; Cottet, A; Joyez, P; Pothier, H; Urbina, C; Esteve, D; Devoret, M H
2002-05-03
We have designed and operated a superconducting tunnel junction circuit that behaves as a two-level atom: the "quantronium." An arbitrary evolution of its quantum state can be programmed with a series of microwave pulses, and a projective measurement of the state can be performed by a pulsed readout subcircuit. The measured quality factor of quantum coherence Qphi approximately 25,000 is sufficiently high that a solid-state quantum processor based on this type of circuit can be envisioned.
Entanglement Dynamics of Two Qubits in a Common Bath
Ma, Jian; Wang, Xiaoguang; Nori, Franco
2012-01-01
We derive a set of hierarchical equations for qubits interacting with a Lorentz-broadened cavity mode at zero temperature, without using the rotating-wave, Born, and Markovian approximations. We use this exact method to reexamine the entanglement dynamics of two qubits interacting with a common bath, which was previously solved only under the rotating-wave and single-excitation approximations. With the exact hierarchy equation method used here, we observe significant differences in the resulting physics, compared to the previous results with various approximations. Double excitations due to counter-rotating-wave terms are also found to have remarkable effects on the dynamics of entanglement.
Teleportation of an Arbitrary Two-qubit State *
Institute of Scientific and Technical Information of China (English)
庞霖; 严瑛白; 金国藩; 韦辉; 郭履容
2001-01-01
A scheme to teleport an unknown two-qubit state from Alice (the sender) to Bob (the receiver) using two Einstein-Podolsky-Rosen (EPR) pairs is presented, each EPR pair being shared by both Alice and Bob. Firstly, Alice combines each of the two particles in the teleported state with an EPR particle and makes Bell state measurement on each combination. Then she transmits the outcomes of her measurements to Bob classically. According to Alice′s measurement results, Bob can perform appropriate unitary operations on his two EPR particles to retrieve the initial state.
Non-unitary probabilistic quantum computing circuit and method
Williams, Colin P. (Inventor); Gingrich, Robert M. (Inventor)
2009-01-01
A quantum circuit performing quantum computation in a quantum computer. A chosen transformation of an initial n-qubit state is probabilistically obtained. The circuit comprises a unitary quantum operator obtained from a non-unitary quantum operator, operating on an n-qubit state and an ancilla state. When operation on the ancilla state provides a success condition, computation is stopped. When operation on the ancilla state provides a failure condition, computation is performed again on the ancilla state and the n-qubit state obtained in the previous computation, until a success condition is obtained.
Quantum homomorphic encryption for polynomial-sized circuits
Y. Dulek (Yfke); C. Schaffner (Christian); F. Speelman (Florian)
2016-01-01
textabstractWe present a new scheme for quantum homomorphic encryption which is compact and allows for efficient evaluation of arbitrary polynomial-sized quantum circuits. Building on the framework of Broadbent and Jeffery [BJ15] and recent results in the area of instantaneous non-local quantum
Improved Classical Simulation of Quantum Circuits Dominated by Clifford Gates.
Bravyi, Sergey; Gosset, David
2016-06-24
We present a new algorithm for classical simulation of quantum circuits over the Clifford+T gate set. The runtime of the algorithm is polynomial in the number of qubits and the number of Clifford gates in the circuit but exponential in the number of T gates. The exponential scaling is sufficiently mild that the algorithm can be used in practice to simulate medium-sized quantum circuits dominated by Clifford gates. The first demonstrations of fault-tolerant quantum circuits based on 2D topological codes are likely to be dominated by Clifford gates due to a high implementation cost associated with logical T gates. Thus our algorithm may serve as a verification tool for near-term quantum computers which cannot in practice be simulated by other means. To demonstrate the power of the new method, we performed a classical simulation of a hidden shift quantum algorithm with 40 qubits, a few hundred Clifford gates, and nearly 50 T gates.
Optimal quantum circuit synthesis from Controlled-U gates
Zhang, J; Sastry, S; Whaley, K B; Zhang, Jun; Vala, Jiri; Sastry, Shankar
2003-01-01
From a geometric approach, we derive the minimum number of applications needed for an arbitrary Controlled-Unitary gate to construct a universal quantum circuit. A new analytic construction procedure is presented and shown to be either optimal or close to optimal. This result can be extended to improve the efficiency of universal quantum circuit construction from any entangling gate. Specifically, for both the Controlled-NOT and Double-CNOT gates, we develop simple analytic ways to construct universal quantum circuits with three applications, which is the least possible.
Emulating weak localization using a solid-state quantum circuit.
Chen, Yu; Roushan, P; Sank, D; Neill, C; Lucero, Erik; Mariantoni, Matteo; Barends, R; Chiaro, B; Kelly, J; Megrant, A; Mutus, J Y; O'Malley, P J J; Vainsencher, A; Wenner, J; White, T C; Yin, Yi; Cleland, A N; Martinis, John M
2014-10-14
Quantum interference is one of the most fundamental physical effects found in nature. Recent advances in quantum computing now employ interference as a fundamental resource for computation and control. Quantum interference also lies at the heart of sophisticated condensed matter phenomena such as Anderson localization, phenomena that are difficult to reproduce in numerical simulations. Here, employing a multiple-element superconducting quantum circuit, with which we manipulate a single microwave photon, we demonstrate that we can emulate the basic effects of weak localization. By engineering the control sequence, we are able to reproduce the well-known negative magnetoresistance of weak localization as well as its temperature dependence. Furthermore, we can use our circuit to continuously tune the level of disorder, a parameter that is not readily accessible in mesoscopic systems. Demonstrating a high level of control, our experiment shows the potential for employing superconducting quantum circuits as emulators for complex quantum phenomena.
Institute of Scientific and Technical Information of China (English)
S. Salimi; A. Mohammadzadet
2011-01-01
Pair coherent state, is a state of a two-mode radiation field that is known as a state with non-gaussian wave function. In this paper, study on the pair coherent state, we notice that with superposition of two first terms of this states, one two-qubits formed. Because of the importance of two-qubits in theory of quantum entanglement, with two different measures with the title of concurrence and D-concurrence, we have studied the amount of entanglement and discussed its details. At the end, we describe these measures for pair coherent states as a function of the amplitude of the SU（2） coherent states.
Institute of Scientific and Technical Information of China (English)
WANG Zhang-Yin; WANG Dong; LIU Jun; SHI Shou-Hua
2006-01-01
We present a scheme for probabilistically teleporting an arbitrary unknown two-qubit state through a quantum channel made up of two nonidentical non-maximally entangled states. In this scheme, the probabilistic teleportation is realized by using a proper positive operator-valued measure instead of usual projective measurement.
Energy Technology Data Exchange (ETDEWEB)
Dong, Li; Xiu, Xiao-Ming, E-mail: xiuxiaomingdl@126.com [Dalian University of Technology, School of Physics and Optoelectronic Technology (China); Ren, Yuan-Peng [Bohai University, Higher Professional Technical Institute (China); Gao, Ya-Jun [Bohai University, College of Mathematics and Physics (China); Yi, X. X. [Dalian University of Technology, School of Physics and Optoelectronic Technology (China)
2013-01-15
We propose a protocol transferring an arbitrary unknown two-qubit state using the quantum channel of a four-qubit genuine entangled state. Simplifying the four-qubit joint measurement to the combination of Bell-state measurements, it can be realized more easily with currently available technologies.
Floating point representations in quantum circuit synthesis
Wiebe, Nathan; Kliuchnikov, Vadym
2013-09-01
We provide a non-deterministic quantum protocol that approximates the single qubit rotations Rx(2ϕ21ϕ22) using Rx(2ϕ1) and Rx(2ϕ2) and a constant number of Clifford and T operations. We then use this method to construct a ‘floating point’ implementation of a small rotation wherein we use the aforementioned method to construct the exponent part of the rotation and also to combine it with a mantissa. This causes the cost of the synthesis to depend more strongly on the relative (rather than absolute) precision required. We analyze the mean and variance of the T-count required to use our techniques and provide new lower bounds for the T-count for ancilla free synthesis of small single-qubit axial rotations. We further show that our techniques can use ancillas to beat these lower bounds with high probability. We also discuss the T-depth of our method and see that the vast majority of the cost of the resultant circuits can be shifted to parallel computation paths.
Quantum noise in large-scale coherent nonlinear photonic circuits
Santori, Charles; Beausoleil, Raymond G; Tezak, Nikolas; Hamerly, Ryan; Mabuchi, Hideo
2014-01-01
A semiclassical simulation approach is presented for studying quantum noise in large-scale photonic circuits incorporating an ideal Kerr nonlinearity. A netlist-based circuit solver is used to generate matrices defining a set of stochastic differential equations, in which the resonator field variables represent random samplings of the Wigner quasi-probability distributions. Although the semiclassical approach involves making a large-photon-number approximation, tests on one- and two-resonator circuits indicate satisfactory agreement between the semiclassical and full-quantum simulation results in the parameter regime of interest. The semiclassical model is used to simulate random errors in a large-scale circuit that contains 88 resonators and hundreds of components in total, and functions as a 4-bit ripple counter. The error rate as a function of on-state photon number is examined, and it is observed that the quantum fluctuation amplitudes do not increase as signals propagate through the circuit, an important...
The sudden Birth and sudden Death of thermal fidelity in a two-qubit XY model
Qin, Li-Guo; Jiang, Ying; Zhang, Hong-Biao
2011-01-01
We study the energy level crossings of the states and thermal fidelity for a two-qubit XY model in the presence of a transverse and inhomogeneous magnetic field. It is shown clearly the effects of the anisotropic factor of the magnetic field through the contour figures of energy level crossing in two subspaces, the isotropy subspace and anisotropy subspace. We calculate the quantum fidelity between the system and the ground state to which the results show the strong effect of the anisotropic factor again. In addition, making use of the transition of Yangian generators in the tensor product space, we study the evolution of the thermal fidelity after the transition. The potential applications of Yangian algebra, as a switch to turn on or off the fidelity, are proposed.
Bidirectional Mapping between a Biphoton Polarization State and a Single-Photon Two-Qubit State
Institute of Scientific and Technical Information of China (English)
LIN Qing
2010-01-01
@@ How to manipulate(operate or measure)single photons efficiently and simply is the basic problem in optical quantum information processing.We first present an efficient scheme to transform a biphoton polarization state to a corresponding single-photon state encoded by its polarization and spatial modes.This single-photon state carries both the information of the controlled and target photons.It will make the realization of bipartite positive-operator-valued measurements efficiently and simply.Moreover,the inverse transformation from the single-photon state back to the corresponding biphoton polarization state is also proposed.Using both the transformations,the realization of the arbitrary two-qubit unitary operation is simple with an M-Z interferometer.All the schemes are feasible with the current experimental technology.
Experimental Demonstration of a Quantum Circuit using Linear Optics Gates
Pittman, T B; Franson, J D
2004-01-01
Probabilistic quantum logic gates can be constructed using linear optical elements, ancilla photons, and post-selection based on the results of measurements. Here we describe an experimental demonstration of a simple quantum circuit that combines two exclusive-OR (XOR) logic gates of that kind. Although circuits using XOR gates are not reversible, they may still be useful in a variety of applications such as generating non-classical states of light.
Quantum Effect in the Mesoscopic RLC Circuits with a Source
Institute of Scientific and Technical Information of China (English)
LIU Jian-Xin; YAN Zhan-Yuan
2005-01-01
The research work on the quantum effects in mesoscopic circuits has undergone a rapid development recently, however the whole quantum theory of the mesoscopic circuits should consider the discreteness of the electric charge. In this paper, based on the fundamental fact that the electric charge takes discrete values, the finite-difference Schrodinger equation of.the mesoscopic RLC circuit with a source is achieved. With a unitary transformation, the Schrodinger equation becomes the standard Mathieu equation, then the energy spectrum and the wave functions of the system are obtained. Using the WKBJ method, the average of currents and square of the current are calculated. The results show the existence of the current fluctuation, which causes noise in the circuits. This paper is an application of the whole quantum mesoscopic circuits theory to the fundamental circuits, and the results will shed light on the design of the miniation circuits, especially on the purpose of reducing quantum noise coherent controlling of the mesoscopic quantum states.
Relaxation of coherent states in a two-qubit NMR quadrupole system
Energy Technology Data Exchange (ETDEWEB)
Sarthour, R.S.; Guimaraes, A.P.; Oliveira, I.S. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Azevedo, E.R. de; Bonk, F.A.; Vidoto, E.L.G.; Bonagamba, T.J. [Universidade de Sao Paulo (IFSC/USP), Sao Carlos, SP (Brazil). Inst. de Fisica; Freitas, J.C.C. [Universidade Federal do Espirito Santo (UFES), Vitoria, ES (Brazil). Dept. de Fisica
2003-07-01
Full text: Pulse Nuclear Magnetic Resonance (NMR) is one of the most serious candidates as an experimental technique for implementing quantum algorithms. To the present date, this technique is in fact the only one where full demonstrations of quantum algorithms implementations have been carried out, in spite of various technical difficulties. On NMR quantum computers, gates and subroutines are encoded as radiofrequency pulse sequences, which must act over coherent states. These sequences usually take tens of milliseconds to be implemented, and during this time the system relax towards equilibrium. Therefore, studies of relaxation times are very important to the realization of quantum algorithms via NMR. In this work we studied the longitudinal relaxation of various coherent states on the NMR quantum computing two-qubit quadrupole system, {sup 23}Na in C{sub 10}H{sub 21}NaO{sub 4}S liquid crystal at room temperature. Relaxation of pseudo-pure states |00>, |01>, |10>, |11>, pseudo-Bell states |01> + |10> and |00> + |11> and Hadamard states |00> + |01> and |10> + |11> were investigated. Experimental curves follow a multi exponential model of relaxation which takes into account mixed, dipolar magnetic and quadrupolar electric interactions. (author)
Decoherence of two-qubit systems: a random matrix description
Pineda, C.; Gorin, T.; Seligman, T. H.
2007-04-01
We study decoherence of two non-interacting qubits. The environment and its interaction with the qubits are modelled by random matrices. Decoherence, measured in terms of purity, is calculated in linear response approximation. Monte Carlo simulations illustrate the validity of this approximation and of its extension by exponentiation. The results up to this point are also used to study one-qubit decoherence. Purity decay of entangled and product states are qualitatively similar though for the latter case it is slower. Numerical studies for a Bell pair as initial state reveal a one to one correspondence between its decoherence and its internal entanglement decay. For strong and intermediate coupling to the environment this correspondence agrees with the one for Werner states. In the limit of a large environment the evolution induces a unital channel in the two qubits, providing a partial explanation for the above relation.
Decoherence of two qubit systems: A random matrix description
Pineda, C; Seligman, T H
2007-01-01
We study decoherence of two non-interacting qubits. The environment and its interaction with the qubits are modelled by random matrices. Decoherence, measured in terms of purity, is calculated in linear response approximation. Monte Carlo simulations illustrate the validity of this approximation and of its extension by exponentiation. The results up to this point are also used to study one qubit decoherence. Purity decay of entangled and product states are qualitatively similar though for the latter case it is slower. Numerical studies for a Bell pair as initial state reveal a one to one correspondence between its decoherence and its internal entanglement decay. For strong and intermediate coupling to the environment this correspondence agrees with the one for Werner states. In the limit of a large environment the evolution induces a unital channel in the two qubits, providing a partial explanation for the relation above.
Quantum information processing with superconducting circuits: a review
Wendin, G.
2017-10-01
During the last ten years, superconducting circuits have passed from being interesting physical devices to becoming contenders for near-future useful and scalable quantum information processing (QIP). Advanced quantum simulation experiments have been shown with up to nine qubits, while a demonstration of quantum supremacy with fifty qubits is anticipated in just a few years. Quantum supremacy means that the quantum system can no longer be simulated by the most powerful classical supercomputers. Integrated classical-quantum computing systems are already emerging that can be used for software development and experimentation, even via web interfaces. Therefore, the time is ripe for describing some of the recent development of superconducting devices, systems and applications. As such, the discussion of superconducting qubits and circuits is limited to devices that are proven useful for current or near future applications. Consequently, the centre of interest is the practical applications of QIP, such as computation and simulation in Physics and Chemistry.
Quantum Wavefunctions and Fluctuations of Mesoscopic RLC Circuit
Institute of Scientific and Technical Information of China (English)
WANG Ji-Suo; LIU Tang-Kun; ZHAN Ming-Sheng
2000-01-01
The quantum wavefunctions and the corresponding energy levels of a RLC (Resistance-Inductance-Capacity) electric circuit are obtained by using canonical quantization method and unitary transformation from the classical equation of motion. The quantum fluctuations of charge and current in an arbitrary eigenstate of the system have also been given as wellas the uncertainty relation. It is showed that even if at 0 K charge and current in the circuit exhibit quantum fluctuations, which originates from fluctuations of zero point vibrations of the system.
Quantum Simulation of the Ultrastrong Coupling Dynamics in Circuit QED
Ballester, D; García-Ripoll, J J; Deppe, F; Solano, E
2011-01-01
We propose a method to get experimental access to the physics of the ultrastrong (USC) and deep strong (DSC) coupling regimes of light-matter interaction through the quantum simulation of their dynamics in standard circuit QED. The method makes use of a two-tone driving scheme, using state-of-the-art circuit-QED technology, and can be easily extended to general quantum optical cavity-QED setups. We provide examples of USC/DSC quantum effects that would be otherwise unaccessible.
Efficient quantum circuits for dense circulant and circulant like operators
Zhou, S. S.; Wang, J. B.
2017-05-01
Circulant matrices are an important family of operators, which have a wide range of applications in science and engineering-related fields. They are, in general, non-sparse and non-unitary. In this paper, we present efficient quantum circuits to implement circulant operators using fewer resources and with lower complexity than existing methods. Moreover, our quantum circuits can be readily extended to the implementation of Toeplitz, Hankel and block circulant matrices. Efficient quantum algorithms to implement the inverses and products of circulant operators are also provided, and an example application in solving the equation of motion for cyclic systems is discussed.
Characterizing error propagation in quantum circuits: the Isotropic Index
Fonseca de Oliveira, André L.; Buksman, Efrain; Cohn, Ilan; García López de Lacalle, Jesús
2017-02-01
This paper presents a novel index in order to characterize error propagation in quantum circuits by separating the resultant mixed error state in two components: an isotropic component that quantifies the lack of information, and a disalignment component that represents the shift between the current state and the original pure quantum state. The Isotropic Triangle, a graphical representation that fits naturally with the proposed index, is also introduced. Finally, some examples with the analysis of well-known quantum algorithms degradation are given.
Multimode circuit quantum electrodynamics with hybrid metamaterial transmission lines.
Egger, D J; Wilhelm, F K
2013-10-18
Quantum transmission lines are central to superconducting and hybrid quantum computing. In this work we show how coupling them to a left-handed transmission line allows circuit QED to reach a new regime: multimode ultrastrong coupling. Out of the many potential applications of this novel device, we discuss the preparation of multipartite entangled states and the simulation of the spin-boson model where a quantum phase transition is reached up to finite size effects.
Stimulating Uncertainty: Amplifying the Quantum Vacuum with Superconducting Circuits
Nation, P D; Blencowe, M P; Nori, Franco
2011-01-01
The ability to generate particles from the quantum vacuum is one of the most pro- found consequences of Heisenberg's uncertainty principle. Although the significance of vacuum fluctuations can be seen throughout physics, the experimental realization of vacuum amplification effects has until now been limited to a few cases. Superconducting circuit devices, driven by the goal to achieve a viable quantum computer, may soon be able to realize the elusive verification of the dynamical Casimir effect and analogue Hawking radiation. This article describes several mechanisms for generating photons from the quantum vacuum and emphasizes their connection to the well-known parametric amplifier from quantum optics. Discussed in detail is the possible realization of each mechanism, or its analogue, in superconducting circuit systems. The ability to selectively engineer these circuit devices highlights the relationship between the various amplification mechanisms.
Colloquium: Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits
Nation, P. D.; Johansson, J. R.; Blencowe, M. P.; Nori, Franco
2012-01-01
The ability to generate particles from the quantum vacuum is one of the most profound consequences of Heisenberg’s uncertainty principle. Although the significance of vacuum fluctuations can be seen throughout physics, the experimental realization of vacuum amplification effects has until now been limited to a few cases. Superconducting circuit devices, driven by the goal to achieve a viable quantum computer, have been used in the experimental demonstration of the dynamical Casimir effect, and may soon be able to realize the elusive verification of analog Hawking radiation. This Colloquium article describes several mechanisms for generating photons from the quantum vacuum and emphasizes their connection to the well-known parametric amplifier from quantum optics. Discussed in detail is the possible realization of each mechanism, or its analog, in superconducting circuit systems. The ability to selectively engineer these circuit devices highlights the relationship between the various amplification mechanisms.
Resilience of the quantum Rabi model in circuit QED
E Manucharyan, Vladimir; Baksic, Alexandre; Ciuti, Cristiano
2017-07-01
In circuit quantum electrodynamics (circuit QED), an artificial ‘circuit atom’ can couple to a quantized microwave radiation much stronger than its real atomic counterpart. The celebrated quantum Rabi model describes the simplest interaction of a two-level system with a single-mode boson field. When the coupling is large enough, the bare multilevel structure of a realistic circuit atom cannot be ignored even if the circuit is strongly anharmonic. We explored this situation theoretically for flux (fluxonium) and charge (Cooper pair box) type multi-level circuits tuned to their respective flux/charge degeneracy points. We identified which spectral features of the quantum Rabi model survive and which are renormalized for large coupling. Despite significant renormalization of the low-energy spectrum in the fluxonium case, the key quantum Rabi feature—nearly-degenerate vacuum consisting of an atomic state entangled with a multi-photon field—appears in both types of circuits when the coupling is sufficiently large. Like in the quantum Rabi model, for very large couplings the entanglement spectrum is dominated by only two, nearly equal eigenvalues, in spite of the fact that a large number of bare atomic states are actually involved in the atom-resonator ground state. We interpret the emergence of the two-fold degeneracy of the vacuum of both circuits as an environmental suppression of flux/charge tunneling due to their dressing by virtual low-/high-impedance photons in the resonator. For flux tunneling, the dressing is nothing else than the shunting of a Josephson atom with a large capacitance of the resonator. Suppression of charge tunneling is a manifestation of the dynamical Coulomb blockade of transport in tunnel junctions connected to resistive leads.
Design infrastructure for Rapid Single Flux Quantum circuits
Toepfer, Hannes; Ortlepp, Thomas
2009-11-01
Cryoelectronic integrated circuits based on Rapid Single Flux Quantum (RSFQ) technology are promising candidates for realizing systems exhibiting very high performance in combination with very low-power consumption. Like other superconductive logic circuits, they are characterized by a high switching speed. Their unique feature consists in the particular representation of binary information by means of short transient voltage pulses. The development of RSFQ circuits and systems requires a comprehensive design approach, supported by appropriate tools. Within the recent years, a dedicated design infrastructure has been developed in Europe in close association with a foundry for digital RSFQ integrated circuits. As a result, RSFQ technology has matured to such a level that engineering efforts enable the development of integrated circuits. In the contribution, the basic features of the RSFQ circuit design are addressed within the context of technical and infrastructural issues of implementation from a European perspective.
Institute of Scientific and Technical Information of China (English)
QIN Meng
2013-01-01
We examine entanglement teleportation,characterized by average fidelity,of two-qubit XY Z spin chain under different nonuniform magnetic field.The entanglement teleportation and the fidelity of entanglement teleportation are investigated separately.We show explicitly that the fidelity of entanglement teleportation can be enhanced by changing the direction of the magnetic field.This means that we can always get optimal fidelity by choosing the directions of magnetic field in the process of quantum teleportation.Moreover,the results show that in some cases the ferromagnetic chain aiso is a quaiified candidate in the process of teleportation protocol.
Decomposition of Unitary Matrices for Finding Quantum Circuits
Daskin, Anmer
2010-01-01
Constructing appropriate unitary matrix operators for new quantum algorithms and finding the minimum cost gate sequences for the implementation of these unitary operators is of fundamental importance in the field of quantum information and quantum computation. Here, we use the group leaders optimization algorithm, which is an effective and simple global optimization algorithm, to decompose a given unitary matrix into a proper-minimum cost quantum gate sequence. Using this procedure, we present new circuit designs for the simulation of the Toffoli gate, the amplification step of the Grover search algorithm, the quantum Fourier transform, the sender part of the quantum teleportation and the Hamiltonian for the Hydrogen molecule. In addition, we give two algorithmic methods for the construction of unitary matrices with respect to the different types of the quantum control gates. Our results indicate that the procedure is effective, general, and easy to implement.
Simulating Zeno physics by a quantum quench with superconducting circuits
Tong, Qing-Jun; An, Jun-Hong; Kwek, L. C.; Luo, Hong-Gang; Oh, C. H.
2014-06-01
Studying out-of-equilibrium physics in quantum systems under quantum quench is of vast experimental and theoretical interest. Using periodic quantum quenches, we present an experimentally accessible scheme to simulate the quantum Zeno and anti-Zeno effects in an open quantum system of a single superconducting qubit interacting with an array of transmission line resonators. The scheme is based on the following two observations: First, compared with conventional systems, the short-time nonexponential decay in our superconducting circuit system is readily observed; and second, a quench-off process mimics an ideal projective measurement when its time duration is sufficiently long. Our results show the active role of quantum quench in quantum simulation and control.
Measurement Saves CNOT Gates in Optimal 2-Qubit Circuits
Shende, V V; Shende, Vivek V.; Markov, Igor L.
2005-01-01
It has been shown in recent papers that any 2-qubit unitary operator can be realized, up to global phase, by a quantum circuit with at most three CNOT gates. Three CNOT gates are also necessary for many operators. However, these results do not fully account for the effect of measurement. Intuitively, the fact that information is lost during measurement should allow some flexibility during circuit synthesis. In our present work, we formalize this in the case of two-qubit operators followed by projective measurements with respect to the computational basis. We show that, in this context, two CNOT gates and six one-qubit gates suffice to simulate an arbitrary two-qubit operator. We also show that for several types of measurement, two CNOT gates are also necessary. In one case, we show that one CNOT gate is necessary and sufficient.
Compressed quantum computation using a remote five-qubit quantum computer
Hebenstreit, M.; Alsina, D.; Latorre, J. I.; Kraus, B.
2017-05-01
The notion of compressed quantum computation is employed to simulate the Ising interaction of a one-dimensional chain consisting of n qubits using the universal IBM cloud quantum computer running on log2(n ) qubits. The external field parameter that controls the quantum phase transition of this model translates into particular settings of the quantum gates that generate the circuit. We measure the magnetization, which displays the quantum phase transition, on a two-qubit system, which simulates a four-qubit Ising chain, and show its agreement with the theoretical prediction within a certain error. We also discuss the relevant point of how to assess errors when using a cloud quantum computer with a limited amount of runs. As a solution, we propose to use validating circuits, that is, to run independent controlled quantum circuits of similar complexity to the circuit of interest.
Quantum interface between an electrical circuit and a single atom
Kielpinski, D; Woolley, M J; Milburn, G J; Taylor, J M
2011-01-01
We show how to bridge the divide between atomic systems and electronic devices by engineering a coupling between the motion of a single ion and the quantized electric field of a resonant circuit. Our method can be used to couple the internal state of an ion to the quantized circuit with the same speed as the internal-state coupling between two ions. All the well-known quantum information protocols linking ion internal and motional states can be converted to protocols between circuit photons and ion internal states. Our results enable quantum interfaces between solid state qubits, atomic qubits, and light, and lay the groundwork for a direct quantum connection between electrical and atomic metrology standards.
Quantum circuit physical design methodology with emphasis on physical synthesis
Mohammadzadeh, Naser; Saheb Zamani, Morteza; Sedighi, Mehdi
2013-11-01
In our previous works, we have introduced the concept of "physical synthesis" as a method to consider the mutual effects of quantum circuit synthesis and physical design. While physical synthesis can involve various techniques to improve the characteristics of the resulting quantum circuit, we have proposed two techniques (namely gate exchanging and auxiliary qubit selection) to demonstrate the effectiveness of the physical synthesis. However, the previous contributions focused mainly on the physical synthesis concept, and the techniques were proposed only as a proof of concept. In this paper, we propose a methodological framework for physical synthesis that involves all previously proposed techniques along with a newly introduced one (called auxiliary qubit insertion). We will show that the entire flow can be seen as one monolithic methodology. The proposed methodology is analyzed using a large set of benchmarks. Experimental results show that the proposed methodology decreases the average latency of quantum circuits by about 36.81 % for the attempted benchmarks.
Characterization of optical quantum circuits using resonant phase shifts
Poot, Menno
2016-01-01
We demonstrate that important information about linear optical circuits can be obtained through the phase shift induced by integrated optical resonators. As a proof of principle, the phase of an unbalanced Mach-Zehnder interferometer is determined. Then the method is applied to a complex optical circuit designed for linear optical quantum computation. In this controlled-NOT gate with qubit initialization and tomography stages, the relative phases are determined as well as the coupling ratios of its directional couplers.
Exact quantum Bayesian rule for qubit measurements in circuit QED
Feng, Wei; Liang, Pengfei; Qin, Lupei; Li, Xin-Qi
2016-02-01
Developing efficient framework for quantum measurements is of essential importance to quantum science and technology. In this work, for the important superconducting circuit-QED setup, we present a rigorous and analytic solution for the effective quantum trajectory equation (QTE) after polaron transformation and converted to the form of Stratonovich calculus. We find that the solution is a generalization of the elegant quantum Bayesian approach developed in arXiv:1111.4016 by Korotokov and currently applied to circuit-QED measurements. The new result improves both the diagonal and off-diagonal elements of the qubit density matrix, via amending the distribution probabilities of the output currents and several important phase factors. Compared to numerical integration of the QTE, the resultant quantum Bayesian rule promises higher efficiency to update the measured state, and allows more efficient and analytical studies for some interesting problems such as quantum weak values, past quantum state, and quantum state smoothing. The method of this work opens also a new way to obtain quantum Bayesian formulas for other systems and in more complicated cases.
Specification of photonic circuits using Quantum Hardware Description Language
Tezak, Nikolas; Pavlichin, Dmitri S; Sarma, Gopal; Mabuchi, Hideo
2011-01-01
Following the simple observation that the interconnection of a set of quantum optical input-output devices can be specified using structural mode VHSIC Hardware Description Language (VHDL), we demonstrate a computer-aided schematic capture workflow for modeling and simulating multi-component photonic circuits. We describe an algorithm for parsing circuit descriptions to derive quantum equations of motion, illustrate our approach using simple examples based on linear and cavity-nonlinear optical components, and demonstrate a computational approach to hierarchical model reduction.
Exploring Quantum Dot Cellular Automata Based Reversible Circuit
Directory of Open Access Journals (Sweden)
Saroj Kumar Chandra
2012-03-01
Full Text Available Quantum-dot Cellular Automata (QCA is a new technology for development of logic circuits based on nanotechnology, and it is an one of the alternative for designing high performance computing over existing CMOS technology. The basic logic in QCA does not use voltage level for logic representation rather it represent binary state by polarization of electrons on the Quantum Cell which is basic building block of QCA. Extensive work is going on QCA for circuit design due to low power consumption and regularity in the circuit.. Clocking is used in QCA circuit to synchronize and control the information flow and to provide the power to run the circuit. Reversible logic design is a well-known paradigm in digital computation, and if circuit developed is reversible then it consumes very low power . Here, in this paper we are presenting a Reversible Universal Gate (RUG based on Quantum-dot Cellular Automata (QCA. The RUG implemented by QCA Designer tool and also its behavior is simulated by it.
Exploring Quantum Dot Cellular Automata Based Reversible Circuit
Directory of Open Access Journals (Sweden)
Saroj Kumar Chandra
2012-03-01
Full Text Available Quantum-dot Cellular Automata (QCA is a new technology for development of logic circuits based on nanotechnology, and it is an one of the alternative for designing high performance computing over existing CMOS technology. The basic logic in QCA does not use voltage level for logic representation rather it represent binary state by polarization of electrons on the Quantum Cell which is basic building block of QCA. Extensive work is going on QCA for circuit design due to low power consumption and regularity in the circuit.. Clocking is used in QCA circuit to synchronize and control the information flow and to provide the power to run the circuit. Reversible logic design is a well-known paradigm in digital computation, and if circuit developed is reversible then it consumes very low power. Here, in this paper we are presenting a Reversible Universal Gate (RUG based on Quantum-dot Cellular Automata (QCA. The RUG implemented by QCA Designer tool and also its behavior is simulated by it.
Derandomizing Quantum Circuits with Measurement-Based Unitary Designs
Turner, Peter S.; Markham, Damian
2016-05-01
Entangled multipartite states are resources for universal quantum computation, but they can also give rise to ensembles of unitary transformations, a topic usually studied in the context of random quantum circuits. Using several graph state techniques, we show that these resources can "derandomize" circuit results by sampling the same kinds of ensembles quantum mechanically, analogously to a quantum random number generator. Furthermore, we find simple examples that give rise to new ensembles whose statistical moments exactly match those of the uniformly random distribution over all unitaries up to order t , while foregoing adaptive feedforward entirely. Such ensembles—known as t designs—often cannot be distinguished from the "truly" random ensemble, and so they find use in many applications that require this implied notion of pseudorandomness.
Emulating a mesoscopic system using superconducting quantum circuits
Chen, Yu; Barends, R.; Bochmann, J.; Campbell, B.; Chiaro, B.; Jeffrey, E.; Kelly, J.; Mariantoni, M.; Megrant, A.; Mutus, J.; Neill, C.; O'Malley, P.; Ohya, S.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T.; Cleland, A. N.; Martinis, J. M.
2013-03-01
We demonstrate an emulation of a mesoscopic system using superconducting quantum circuits. Taking advantage of our ReZQu-architectured quantum processor, we controllably splitted a microwave photon and manipulated the splitted photons before they recombined for detection. In this way, we were able to simulate the weak localization effect in mesoscopic systems - a coherent backscattering process due to quantum interference. The influence of the phase coherence was investigated by tuning the coherence time of the quantum circuit, which in turn mimics the temperature effect on the weak localization process. At the end, we demonstrated an effect resembling universal conductance fluctuations, which arises from the frequency beating between different coherent backscattering processes. The universality of the observed fluctuation was shown as the independence of the fluctuation amplitude on detailed experimental conditions.
Parallel Quantum Circuit in a Tunnel Junction
Faizy Namarvar, Omid; Dridi, Ghassen; Joachim, Christian
2016-07-01
Spectral analysis of 1 and 2-states per line quantum bus are normally sufficient to determine the effective Vab(N) electronic coupling between the emitter and receiver states through the bus as a function of the number N of parallel lines. When Vab(N) is difficult to determine, an Heisenberg-Rabi time dependent quantum exchange process must be triggered through the bus to capture the secular oscillation frequency Ωab(N) between those states. Two different linear and regimes are demonstrated for Ωab(N) as a function of N. When the initial preparation is replaced by coupling of the quantum bus to semi-infinite electrodes, the resulting quantum transduction process is not faithfully following the Ωab(N) variations. Because of the electronic transparency normalisation to unity and of the low pass filter character of this transduction, large Ωab(N) cannot be captured by the tunnel junction. The broadly used concept of electrical contact between a metallic nanopad and a molecular device must be better described as a quantum transduction process. At small coupling and when N is small enough not to compensate for this small coupling, an N2 power law is preserved for Ωab(N) and for Vab(N).
Parallel Quantum Circuit in a Tunnel Junction.
Faizy Namarvar, Omid; Dridi, Ghassen; Joachim, Christian
2016-07-25
Spectral analysis of 1 and 2-states per line quantum bus are normally sufficient to determine the effective Vab(N) electronic coupling between the emitter and receiver states through the bus as a function of the number N of parallel lines. When Vab(N) is difficult to determine, an Heisenberg-Rabi time dependent quantum exchange process must be triggered through the bus to capture the secular oscillation frequency Ωab(N) between those states. Two different linear and regimes are demonstrated for Ωab(N) as a function of N. When the initial preparation is replaced by coupling of the quantum bus to semi-infinite electrodes, the resulting quantum transduction process is not faithfully following the Ωab(N) variations. Because of the electronic transparency normalisation to unity and of the low pass filter character of this transduction, large Ωab(N) cannot be captured by the tunnel junction. The broadly used concept of electrical contact between a metallic nanopad and a molecular device must be better described as a quantum transduction process. At small coupling and when N is small enough not to compensate for this small coupling, an N(2) power law is preserved for Ωab(N) and for Vab(N).
Multimode circuit optomechanics near the quantum limit.
Massel, Francesco; Cho, Sung Un; Pirkkalainen, Juha-Matti; Hakonen, Pertti J; Heikkilä, Tero T; Sillanpää, Mika A
2012-01-01
The coupling of distinct systems underlies nearly all physical phenomena. A basic instance is that of interacting harmonic oscillators, giving rise to, for example, the phonon eigenmodes in a lattice. Of particular importance are the interactions in hybrid quantum systems, which can combine the benefits of each part in quantum technologies. Here we investigate a hybrid optomechanical system having three degrees of freedom, consisting of a microwave cavity and two micromechanical beams with closely spaced frequencies around 32 MHz and no direct interaction. We record the first evidence of tripartite optomechanical mixing, implying that the eigenmodes are combinations of one photonic and two phononic modes. We identify an asymmetric dark mode having a long lifetime. Simultaneously, we operate the nearly macroscopic mechanical modes close to the motional quantum ground state, down to 1.8 thermal quanta, achieved by back-action cooling. These results constitute an important advance towards engineering of entangled motional states.
Atomic physics and quantum optics using superconducting circuits.
You, J Q; Nori, Franco
2011-06-29
Superconducting circuits based on Josephson junctions exhibit macroscopic quantum coherence and can behave like artificial atoms. Recent technological advances have made it possible to implement atomic-physics and quantum-optics experiments on a chip using these artificial atoms. This Review presents a brief overview of the progress achieved so far in this rapidly advancing field. We not only discuss phenomena analogous to those in atomic physics and quantum optics with natural atoms, but also highlight those not occurring in natural atoms. In addition, we summarize several prospective directions in this emerging interdisciplinary field.
Synthesis of Arbitrary Quantum Circuits to Topological Assembly
Paler, Alexandru; Devitt, Simon J.; Fowler, Austin G.
2016-08-01
Given a quantum algorithm, it is highly nontrivial to devise an efficient sequence of physical gates implementing the algorithm on real hardware and incorporating topological quantum error correction. In this paper, we present a first step towards this goal, focusing on generating correct and simple arrangements of topological structures that correspond to a given quantum circuit and largely neglecting their efficiency. We detail the many challenges that will need to be tackled in the pursuit of efficiency. The software source code can be consulted at https://github.com/alexandrupaler/tqec.
Two-dimensional lattice gauge theories with superconducting quantum circuits
Energy Technology Data Exchange (ETDEWEB)
Marcos, D., E-mail: david.marcos@me.com [Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Widmer, P. [Albert Einstein Center, Institute for Theoretical Physics, Bern University, CH-3012, Bern (Switzerland); Rico, E. [IPCMS (UMR 7504) and ISIS (UMR 7006), University of Strasbourg and CNRS, 67000 Strasbourg (France); Hafezi, M. [Joint Quantum Institute, NIST/University of Maryland, College Park 20742 (United States); Department of Electrical Engineering and Institute for Research in Electronics and Applied Physics, University of Maryland, College Park, MD 20742 (United States); Rabl, P. [Institute of Atomic and Subatomic Physics, TU Wien, Stadionallee 2, 1020 Wien (Austria); Wiese, U.-J. [Albert Einstein Center, Institute for Theoretical Physics, Bern University, CH-3012, Bern (Switzerland); Zoller, P. [Institute for Quantum Optics and Quantum Information of the Austrian Academy of Sciences, A-6020 Innsbruck (Austria); Institute for Theoretical Physics, University of Innsbruck, A-6020 Innsbruck (Austria)
2014-12-15
A quantum simulator of U(1) lattice gauge theories can be implemented with superconducting circuits. This allows the investigation of confined and deconfined phases in quantum link models, and of valence bond solid and spin liquid phases in quantum dimer models. Fractionalized confining strings and the real-time dynamics of quantum phase transitions are accessible as well. Here we show how state-of-the-art superconducting technology allows us to simulate these phenomena in relatively small circuit lattices. By exploiting the strong non-linear couplings between quantized excitations emerging when superconducting qubits are coupled, we show how to engineer gauge invariant Hamiltonians, including ring-exchange and four-body Ising interactions. We demonstrate that, despite decoherence and disorder effects, minimal circuit instances allow us to investigate properties such as the dynamics of electric flux strings, signaling confinement in gauge invariant field theories. The experimental realization of these models in larger superconducting circuits could address open questions beyond current computational capability.
Coupling single emitters to quantum plasmonic circuits
Huck, Alexander; Andersen, Ulrik L.
2016-09-01
In recent years, the controlled coupling of single-photon emitters to propagating surface plasmons has been intensely studied, which is fueled by the prospect of a giant photonic nonlinearity on a nanoscaled platform. In this article, we will review the recent progress on coupling single emitters to nanowires towards the construction of a new platform for strong light-matter interaction. The control over such a platform might open new doors for quantum information processing and quantum sensing at the nanoscale and for the study of fundamental physics in the ultrastrong coupling regime.
Coupling single emitters to quantum plasmonic circuits
Huck, Alexander
2016-01-01
In recent years the controlled coupling of single photon emitters to propagating surface plasmons has been intensely studied, which is fueled by the prospect of a giant photonic non-linearity on a nano-scaled platform. In this article we will review the recent progress on coupling single emitters to nano-wires towards the construction of a new platform for strong light-matter interaction. The control over such a platform might open new doors for quantum information processing and quantum sensing at the nanoscale, and for the study of fundamental physics in the ultra-strong coupling regime.
Lasing without inversion in circuit quantum electrodynamics.
Marthaler, M; Utsumi, Y; Golubev, D S; Shnirman, A; Schön, Gerd
2011-08-26
We study the photon generation in a transmission line oscillator coupled to a driven qubit in the presence of a dissipative electromagnetic environment. It has been demonstrated previously that a population inversion in the qubit can lead to a lasing state of the oscillator. Here we show that the circuit can also exhibit the effect of "lasing without inversion." It arises since the coupling to the dissipative environment enhances photon emission as compared to absorption, similar to the recoil effect predicted for atomic systems. While the recoil effect is very weak, and so far elusive, the effect described here should be observable with realistic circuits. We analyze the requirements for system parameters and environment.
Quantum localization through interference on homoclinic and heteroclinic circuits
Energy Technology Data Exchange (ETDEWEB)
III, E L Sibert; Borondo, F [Departamento de Quimica C-IX and Instituto Mixto de Ciencias Matematicas CSIC-UAM-UC3M-UCM, Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid (Spain); Vergini, E; Benito, R M [Grupo de Sistemas Complejos and Departamento de FIsica, Escuela Tecnica Superior de Ingenieros Agronomos, Universidad Politecnica de Madrid, 28040 Madrid (Spain)], E-mail: sibert@chem.wisc.edu, E-mail: eduardogerman.vergini@upm.es, E-mail: rosamaria.benito@upm.es, E-mail: f.borondo@uam.es
2008-05-15
Localization effects due to scarring constitute one of the clearest indications of the relevance of interference in the transport of quantum probability density along quantized closed circuits in phase space. The corresponding path can be obvious, such as the scarring periodic orbit (PO) itself which produces time recurrences at multiples of the period. However, there are others more elaborate which only close asymptotically, for example, those associated with homoclinic and heteroclinic orbits. In this paper, we demonstrate that these circuits are also able to produce recurrences but at (semiclassically) longer times, of the order of the Ehrenfest time. The most striking manifestation of this phenomenon is the accumulation of quantum probability density along the corresponding circuits. The discussion is illustrated with an example corresponding to a typical PO of the quartic two-dimensional oscillator.
Gallium Arsenide (GaAs) Quantum Photonic Waveguide Circuits
Wang, Jianwei; Jiang, Pisu; Bonneau, Damien; Engin, Erman; Silverstone, Joshua W; Lermer, Matthias; Beetz, Johannes; Kamp, Martin; Hofling, Sven; Tanner, Michael G; Natarajan, Chandra M; Hadfield, Robert H; Dorenbos, Sander N; Zwiller, Val; O'Brien, Jeremy L; Thompson, Mark G
2014-01-01
Integrated quantum photonics is a promising approach for future practical and large-scale quantum information processing technologies, with the prospect of on-chip generation, manipulation and measurement of complex quantum states of light. The gallium arsenide (GaAs) material system is a promising technology platform, and has already successfully demonstrated key components including waveguide integrated single-photon sources and integrated single-photon detectors. However, quantum circuits capable of manipulating quantum states of light have so far not been investigated in this material system. Here, we report GaAs photonic circuits for the manipulation of single-photon and two-photon states. Two-photon quantum interference with a visibility of 94.9 +/- 1.3% was observed in GaAs directional couplers. Classical and quantum interference fringes with visibilities of 98.6 +/- 1.3% and 84.4 +/- 1.5% respectively were demonstrated in Mach-Zehnder interferometers exploiting the electro-optic Pockels effect. This w...
Ancilla-driven instantaneous quantum polynomial time circuit for quantum supremacy
Takeuchi, Yuki; Takahashi, Yasuhiro
2016-12-01
Instantaneous quantum polynomial time (IQP) is a model of (probably) nonuniversal quantum computation. Since it has been proven that IQP circuits are unlikely to be simulated classically up to a multiplicative error and an error in the l1 norm, IQP is considered as one of the promising classes that demonstrates quantum supremacy. Although IQP circuits can be realized more easily than a universal quantum computer, demonstrating quantum supremacy is still difficult. It is therefore desired to find subclasses of IQP that are easy to implement. In this paper, by imposing some restrictions on IQP, we propose ancilla-driven IQP (ADIQP) as the subclass of commuting quantum computation suitable for many experimental settings. We show that even though ADIQP circuits are strictly weaker than IQP circuits in a sense, they are also hard to simulate classically up to a multiplicative error and an error in the l1 norm. Moreover, the properties of ADIQP make it easy to investigate the verifiability of ADIQP circuits and the difficulties in realizing ADIQP circuits.
Large-scale quantum photonic circuits in silicon
Harris, Nicholas C.; Bunandar, Darius; Pant, Mihir; Steinbrecher, Greg R.; Mower, Jacob; Prabhu, Mihika; Baehr-Jones, Tom; Hochberg, Michael; Englund, Dirk
2016-08-01
Quantum information science offers inherently more powerful methods for communication, computation, and precision measurement that take advantage of quantum superposition and entanglement. In recent years, theoretical and experimental advances in quantum computing and simulation with photons have spurred great interest in developing large photonic entangled states that challenge today's classical computers. As experiments have increased in complexity, there has been an increasing need to transition bulk optics experiments to integrated photonics platforms to control more spatial modes with higher fidelity and phase stability. The silicon-on-insulator (SOI) nanophotonics platform offers new possibilities for quantum optics, including the integration of bright, nonclassical light sources, based on the large third-order nonlinearity (χ(3)) of silicon, alongside quantum state manipulation circuits with thousands of optical elements, all on a single phase-stable chip. How large do these photonic systems need to be? Recent theoretical work on Boson Sampling suggests that even the problem of sampling from e30 identical photons, having passed through an interferometer of hundreds of modes, becomes challenging for classical computers. While experiments of this size are still challenging, the SOI platform has the required component density to enable low-loss and programmable interferometers for manipulating hundreds of spatial modes. Here, we discuss the SOI nanophotonics platform for quantum photonic circuits with hundreds-to-thousands of optical elements and the associated challenges. We compare SOI to competing technologies in terms of requirements for quantum optical systems. We review recent results on large-scale quantum state evolution circuits and strategies for realizing high-fidelity heralded gates with imperfect, practical systems. Next, we review recent results on silicon photonics-based photon-pair sources and device architectures, and we discuss a path towards
A quantum Fredkin gate (Conference Presentation)
Patel, Raj B.; Ho, Joseph; Ferreyrol, Franck; Ralph, Timothy C.; Pryde, Geoff J.
2016-10-01
One of the greatest challenges in modern science is the realisation of quantum computers which, as their scale increases, will allow enhanced performance of tasks across many areas of quantum information processing. Quantum logic gates play a vital role in realising these applications by carrying out the elementary operations on the qubits; a key aim is minimising the resources needed to build these gates into useful circuits. While the salient features of a quantum computer have been shown in proof-of-principle experiments, e.g., single- and two-qubit gates, difficulties in scaling quantum systems to encode and manipulate multiple qubits has hindered demonstrations of more complex operations. This is exemplified by the classical Fredkin (or controlled-SWAP) gate [1] for which, despite many theoretical proposals [2,3] relying on concatenating multiple two-qubit gates, a quantum analogue has yet to be realised. Here, by directly adding control to a two-qubit SWAP unitary [4], we use photonic qubit logic to report the first experimental demonstration of a quantum Fredkin gate [5]. Our scheme uses linear optics and improves on the overall probability of success by an order of magnitude over previous proposals [2,3]. This optical approach allows us to add control an arbitrary black-box unitary which is otherwise forbidden in the standard circuit model [6]. Additionally, the action of our gate exhibits quantum coherence allowing the generation of the highest fidelity three-photon GHZ states to date. The quantum Fredkin gate has many applications in quantum computing, quantum measurements [7] and cryptography [8,9]. Using our scheme, we apply the Fredkin gate to the task of direct measurements of the purity and state overlap of a quantum system [7] without recourse to quantum state tomography.
Energy Technology Data Exchange (ETDEWEB)
Pahlavani, H., E-mail: h-pahlavani@qom.ac.ir; Kolur, E. Rahmanpour
2016-08-15
Based on the electrical charge discreteness, the Hamiltonian operator for the mutual inductance coupled quantum mesoscopic LC circuits has been found. The persistent current on two driven coupled mesoscopic electric pure L circuits (two quantum loops) has been obtained by using algebraic quantum dynamic approach. The influence of the mutual inductance on energy spectrum and quantum fluctuations of the charge and current for two coupled quantum electric mesoscopic LC circuits have been investigated.
Complete quantum circuit of Haar wavelet based MRA
Institute of Scientific and Technical Information of China (English)
HE Yuguo; SUN Jigui
2005-01-01
Wavelet analysis has applications in many areas, such as signal analysis and image processing. We propose a method for generating the complete circuit of Haar wavelet based MRA by factoring butterfly matrices and conditional perfect shuffle permutation matrices. The factorization of butterfly matrices is the essential part of the design. As a result, it is the key point to obtain the circuits of .I2t()W()I2n-2t-2. In this paper, we use a simple means to develop quantum circuits for this kind of matrices. Similarly, the conditional permutation matrix is implemented entirely, combined with the scheme of Fijany and Williams. The cir-cuits and the ideas adopted in the design are simple and in-telligible.
Liang, Lin-mei; Li, Cheng-zu
2005-02-01
This Letter presents nonlocality without inequalities for two-qubit mixed states. This Letter was mainly sparked by Cabello's work [Phys. Rev. A 65 (2003) 032108] and is an extension of our recent work [Phys. Lett. A 318 (2003) 300].
QUANTUM FLUCTUATIONS IN A MESOSCOPIC DAMPED LC PARALLEL CIRCUIT IN DISPLACED SQUEEZED FOCK STATE
Institute of Scientific and Technical Information of China (English)
GU YONG-JIAN
2001-01-01
We study the quantum effects of a damped LC parallel circuit considering its different performance from an RLC series circuit in classical physics. The damped LC parallel circuit with a source is quantized and the quantum fluctuations of magnetic flux and electric charge in the circuit in displaced squeezed Fock state are investigated. It is shown that, as in the RLC series circuit, the fluctuations only depend on the squeezing parameter and the parameters of the circuit components in the damped LC parallel circuit, but the effects of the circuit components on the fluctuations are different in the two circuits.
Ntalaperas, D
2016-01-01
We propose an architecture based on Quantum cellular Automata which allows the use of only one type of quantum gates per computational step in order to perform nearest neighbor interactions. The model is built in partial steps, each one of them analyzed using nearest neighbor interactions, starting with single qubit operations and continuing with two qubit ones. The effectiveness of the model is tested and valuated by developing a quantum circuit implementing the Quantum Fourier Transform. The important outcome of this validation was that the operations are performed in a local and controlled manner thus reducing the error rate of each computational step.
Einstein-Podolsky-Rosen Steerability Criterion for Two-Qubit Density Matrices
Chen, Jing-Ling; Ye, Xiang-Jun; Wu, Chunfeng; Kwek, L C; Oh, C H
2011-01-01
We propose a criterion ${S}=\\lambda_1+\\lambda_2-(\\lambda_1-\\lambda_2)^2<0$ to detect Einstein-Podolsky-Rosen (EPR) steering for arbitrary two-qubit density matrix $\\rho_{AB}$. Here $\\lambda_1,\\lambda_2$ are respectively the minimal and the second minimal eigenvalues of $\\rho^{T_B}_{AB}$, which is the partial transpose of $\\rho_{AB}$. Numerical results suggest that this criterion is a necessary and sufficient condition for demonstrating steerability of two qubits.
CUGatesDensity—Quantum circuit analyser extended to density matrices
Loke, T.; Wang, J. B.
2013-12-01
CUGatesDensity is an extension of the original quantum circuit analyser CUGates (Loke and Wang, 2011) [7] to provide explicit support for the use of density matrices. The new package enables simulation of quantum circuits involving statistical ensemble of mixed quantum states. Such analysis is of vital importance in dealing with quantum decoherence, measurements, noise and error correction, and fault tolerant computation. Several examples involving mixed state quantum computation are presented to illustrate the use of this package. Catalogue identifier: AEPY_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEPY_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 5368 No. of bytes in distributed program, including test data, etc.: 143994 Distribution format: tar.gz Programming language: Mathematica. Computer: Any computer installed with a copy of Mathematica 6.0 or higher. Operating system: Any system with a copy of Mathematica 6.0 or higher installed. Classification: 4.15. Nature of problem: To simulate arbitrarily complex quantum circuits comprised of single/multiple qubit and qudit quantum gates with mixed state registers. Solution method: A density matrix representation for mixed states and a state vector representation for pure states are used. The construct is based on an irreducible form of matrix decomposition, which allows a highly efficient implementation of general controlled gates with multiple conditionals. Running time: The examples provided in the notebook CUGatesDensity.nb take approximately 30 s to run on a laptop PC.
Institute of Scientific and Technical Information of China (English)
ZHANG Yong; LONG Gui-Lu; WU Yu-Chun; GUO Guang-Can
2007-01-01
Natural thermal entanglement between two qubits with ⅩⅩⅩ Heisenberg interaction is studied. For the antiferromagnet, increasing coupling strength or decreasing temperature under critical point increases the entanglement.Based on the thermal entanglement as quantum channel, entanglement and information of an input entangled state are transferred via partial teleportation. We find that the entanglement transferred will be lost during the process, and for the entanglement fidelity the partial teleportation is superior to classical communication as concurrence of entangled channel beyond 1/4. We show that both correlation information in input entangled state and individual information of the teleported particle are linearly dissipated. With more entanglement in quantum channel, more entanglement and correlation information can be transferred.
Relativistic Quantum Teleportation with superconducting circuits
Friis, Nicolai; Truong, Kevin; Sabín, Carlos; Solano, Enrique; Johansson, Göran; Fuentes, Ivette
2012-01-01
We study the effects of relativistic motion on quantum teleportation and propose a realizable experiment where our results can be tested. We compute bounds on the optimal fidelity of teleportation when one of the observers undergoes non-uniform motion for a finite time. The upper bound to the optimal fidelity is degraded due to the observer's motion however, we discuss how this degradation can be corrected. These effects are observable for experimental parameters that are within reach of cutting-edge superconducting technology.
Energy Technology Data Exchange (ETDEWEB)
Mohamed, A.-B.A., E-mail: abdelbastm@yahoo.com [College of Sciences and Humanities, Prince Sattam Bin Abdulaziz University, Al-Aflaj (Saudi Arabia); Faculty of Science, Assiut University, Assiut (Egypt); Joshi, A., E-mail: mcbamji@gmail.com [Physics Department, Adelphi University Garden City, NY 11530 (United States); Department of Physics and Optical Engineering, RHIT, Terra Haute IN 47803 (United States); Hassan, S.S., E-mail: shoukryhassan@hotmail.com [Department of Mathematics, College of Science, University of Bahrain, P.O. Box 32038 (Bahrain)
2016-03-15
Several quantum-mechanical correlations, notably, quantum entanglement, measurement-induced nonlocality and Bell nonlocality are studied for a two qubit-system having no mutual interaction. Analytical expressions for the measures of these quantum-mechanical correlations of different bipartite partitions of the system are obtained, for initially two entangled qubits and the two photons are in their vacuum states. It is found that the qubits-fields interaction leads to the loss and gain of the initial quantum correlations. The lost initial quantum correlations transfer from the qubits to the cavity fields. It is found that the maximal violation of Bell’s inequality is occurring when the quantum correlations of both the logarithmic negativity and measurement-induced nonlocality reach particular values. The maximal violation of Bell’s inequality occurs only for certain bipartite partitions of the system. The frequency detuning leads to quick oscillations of the quantum correlations and inhibits their transfer from the qubits to the cavity modes. It is also found that the dynamical behavior of the quantum correlation clearly depends on the qubit distribution angle.
Quantum Zeno Effect in the Strong Measurement Regime of Circuit Quantum Electrodynamics
2016-05-17
we report the direct observation of theQZE in a superconducting qubit undergoing continuous strongmeasurement with simultaneous qubit driving...New J. Phys. 18 (2016) 053031 doi:10.1088/1367-2630/18/5/053031 PAPER Quantum Zeno effect in the strongmeasurement regime of circuit quantum...of quantum jumps between states for a qubit beingmeasured continuously at rate Gm is the same as that for a qubit undergoing discretemeasurements at
Quantum simulation with a boson sampling circuit
González Olivares, Diego; Peropadre, Borja; Aspuru-Guzik, Alán; García-Ripoll, Juan José
2016-08-01
In this work we study a system that consists of 2 M matter qubits that interact through a boson sampling circuit, i.e., an M -port interferometer, embedded in two different architectures. We prove that, under the conditions required to derive a master equation, the qubits evolve according to effective bipartite X Y spin Hamiltonians, with or without local and collective dissipation terms. This opens the door to the simulation of any bipartite spin or hard-core boson models and exploring dissipative phase transitions as the competition between coherent and incoherent exchange of excitations. We also show that in the purely dissipative regime this model has a large number of exact and approximate dark states, whose structure and decay rates can be estimated analytically. We finally argue that this system may be used for the adiabatic preparation of boson sampling states encoded in the matter qubits.
Digitized adiabatic quantum computing with a superconducting circuit.
Barends, R; Shabani, A; Lamata, L; Kelly, J; Mezzacapo, A; Las Heras, U; Babbush, R; Fowler, A G; Campbell, B; Chen, Yu; Chen, Z; Chiaro, B; Dunsworth, A; Jeffrey, E; Lucero, E; Megrant, A; Mutus, J Y; Neeley, M; Neill, C; O'Malley, P J J; Quintana, C; Roushan, P; Sank, D; Vainsencher, A; Wenner, J; White, T C; Solano, E; Neven, H; Martinis, John M
2016-06-09
Quantum mechanics can help to solve complex problems in physics and chemistry, provided they can be programmed in a physical device. In adiabatic quantum computing, a system is slowly evolved from the ground state of a simple initial Hamiltonian to a final Hamiltonian that encodes a computational problem. The appeal of this approach lies in the combination of simplicity and generality; in principle, any problem can be encoded. In practice, applications are restricted by limited connectivity, available interactions and noise. A complementary approach is digital quantum computing, which enables the construction of arbitrary interactions and is compatible with error correction, but uses quantum circuit algorithms that are problem-specific. Here we combine the advantages of both approaches by implementing digitized adiabatic quantum computing in a superconducting system. We tomographically probe the system during the digitized evolution and explore the scaling of errors with system size. We then let the full system find the solution to random instances of the one-dimensional Ising problem as well as problem Hamiltonians that involve more complex interactions. This digital quantum simulation of the adiabatic algorithm consists of up to nine qubits and up to 1,000 quantum logic gates. The demonstration of digitized adiabatic quantum computing in the solid state opens a path to synthesizing long-range correlations and solving complex computational problems. When combined with fault-tolerance, our approach becomes a general-purpose algorithm that is scalable.
Hybrid circuit cavity quantum electrodynamics with a micromechanical resonator.
Pirkkalainen, J-M; Cho, S U; Li, Jian; Paraoanu, G S; Hakonen, P J; Sillanpää, M A
2013-02-14
Hybrid quantum systems with inherently distinct degrees of freedom have a key role in many physical phenomena. Well-known examples include cavity quantum electrodynamics, trapped ions, and electrons and phonons in the solid state. In those systems, strong coupling makes the constituents lose their individual character and form dressed states, which represent a collective form of dynamics. As well as having fundamental importance, hybrid systems also have practical applications, notably in the emerging field of quantum information control. A promising approach is to combine long-lived atomic states with the accessible electrical degrees of freedom in superconducting cavities and quantum bits (qubits). Here we integrate circuit cavity quantum electrodynamics with phonons. Apart from coupling to a microwave cavity, our superconducting transmon qubit, consisting of tunnel junctions and a capacitor, interacts with a phonon mode in a micromechanical resonator, and thus acts like an atom coupled to two different cavities. We measure the phonon Stark shift, as well as the splitting of the qubit spectral line into motional sidebands, which feature transitions between the dressed electromechanical states. In the time domain, we observe coherent conversion of qubit excitation to phonons as sideband Rabi oscillations. This is a model system with potential for a quantum interface, which may allow for storage of quantum information in long-lived phonon states, coupling to optical photons or for investigations of strongly coupled quantum systems near the classical limit.
Digitized adiabatic quantum computing with a superconducting circuit
Barends, R.; Shabani, A.; Lamata, L.; Kelly, J.; Mezzacapo, A.; Heras, U. Las; Babbush, R.; Fowler, A. G.; Campbell, B.; Chen, Yu; Chen, Z.; Chiaro, B.; Dunsworth, A.; Jeffrey, E.; Lucero, E.; Megrant, A.; Mutus, J. Y.; Neeley, M.; Neill, C.; O'Malley, P. J. J.; Quintana, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Solano, E.; Neven, H.; Martinis, John M.
2016-06-01
Quantum mechanics can help to solve complex problems in physics and chemistry, provided they can be programmed in a physical device. In adiabatic quantum computing, a system is slowly evolved from the ground state of a simple initial Hamiltonian to a final Hamiltonian that encodes a computational problem. The appeal of this approach lies in the combination of simplicity and generality; in principle, any problem can be encoded. In practice, applications are restricted by limited connectivity, available interactions and noise. A complementary approach is digital quantum computing, which enables the construction of arbitrary interactions and is compatible with error correction, but uses quantum circuit algorithms that are problem-specific. Here we combine the advantages of both approaches by implementing digitized adiabatic quantum computing in a superconducting system. We tomographically probe the system during the digitized evolution and explore the scaling of errors with system size. We then let the full system find the solution to random instances of the one-dimensional Ising problem as well as problem Hamiltonians that involve more complex interactions. This digital quantum simulation of the adiabatic algorithm consists of up to nine qubits and up to 1,000 quantum logic gates. The demonstration of digitized adiabatic quantum computing in the solid state opens a path to synthesizing long-range correlations and solving complex computational problems. When combined with fault-tolerance, our approach becomes a general-purpose algorithm that is scalable.
Quantum dot rolled-up microtube optoelectronic integrated circuit.
Bhowmick, Sishir; Frost, Thomas; Bhattacharya, Pallab
2013-05-15
A rolled-up microtube optoelectronic integrated circuit operating as a phototransceiver is demonstrated. The microtube is made of a InGaAs/GaAs strained bilayer with InAs self-organized quantum dots inserted in the GaAs layer. The phototransceiver consists of an optically pumped microtube laser and a microtube photoconductive detector connected by an a-Si/SiO2 waveguide. The loss in the waveguide and responsivity of the entire phototransceiver circuit are 7.96 dB/cm and 34 mA/W, respectively.
Chaotic phenomena in Josephson circuits coupled quantum cellular neural networks
Institute of Scientific and Technical Information of China (English)
Wang Sen; Cai Li; Li Qin; Wu Gang
2007-01-01
In this paper the nonlinear dynamical behaviour of a quantum cellular neural network (QCNN) by coupling Josephson circuits was investigated and it was shown that the QCNN using only two of them can cause the onset of chaotic oscillation. The theoretical analysis and simulation for the two Josephson-circuits-coupled QCNN have been done by using the amplitude and phase as state variables. The complex chaotic behaviours can be observed and then proved by calculating Lyapunov exponents. The study provides valuable information about QCNNs for future application in high-parallel signal processing and novel chaotic generators.
nLukac, Maarti; Kameyama, Michitaka
2011-01-01
It has been experimentally proven that realizing universal quantum gates using higher-radices logic is practically and technologically possible. We developed a Parallel Genetic Algorithm that synthesizes Boolean reversible circuits realized with a variety of quantum gates on qudits with various radices. In order to allow synthesizing circuits of medium sizes in the higher radix quantum space we performed the experiments using a GPU accelerated Genetic Algorithm. Using the accelerated GA we compare heuristic improvements to the mutation process based on cost minimization, on the adaptive cost of the primitives and improvements due to Baldwinian vs. Lamarckian GA. We also describe various fitness function formulations that allowed for various realizations of well known universal Boolean reversible or quantum-probabilistic circuits.
High-fidelity two-qubit gates via dynamical decoupling of local 1 /f noise at the optimal point
D'Arrigo, A.; Falci, G.; Paladino, E.
2016-08-01
We investigate the possibility of achieving high-fidelity universal two-qubit gates by supplementing optimal tuning of individual qubits with dynamical decoupling (DD) of local 1 /f noise. We consider simultaneous local pulse sequences applied during the gate operation and compare the efficiencies of periodic, Carr-Purcell, and Uhrig DD with hard π pulses along two directions (πz /y pulses). We present analytical perturbative results (Magnus expansion) in the quasistatic noise approximation combined with numerical simulations for realistic 1 /f noise spectra. The gate efficiency is studied as a function of the gate duration, of the number n of pulses, and of the high-frequency roll-off. We find that the gate error is nonmonotonic in n , decreasing as n-α in the asymptotic limit, α ≥2 , depending on the DD sequence. In this limit πz-Urhig is the most efficient scheme for quasistatic 1 /f noise, but it is highly sensitive to the soft UV cutoff. For small number of pulses, πz control yields anti-Zeno behavior, whereas πy pulses minimize the error for a finite n . For the current noise figures in superconducting qubits, two-qubit gate errors ˜10-6 , meeting the requirements for fault-tolerant quantum computation, can be achieved. The Carr-Purcell-Meiboom-Gill sequence is the most efficient procedure, stable for 1 /f noise with UV cutoff up to gigahertz.
Generating three-qubit quantum circuits with neural networks
Swaddle, Michael; Noakes, Lyle; Smallbone, Harry; Salter, Liam; Wang, Jingbo
2017-10-01
A new method for compiling quantum algorithms is proposed and tested for a three qubit system. The proposed method is to decompose a unitary matrix U, into a product of simpler Uj via a neural network. These Uj can then be decomposed into product of known quantum gates. Key to the effectiveness of this approach is the restriction of the set of training data generated to paths which approximate minimal normal subRiemannian geodesics, as this removes unnecessary redundancy and ensures the products are unique. The two neural networks are shown to work effectively, each individually returning low loss values on validation data after relatively short training periods. The two networks are able to return coefficients that are sufficiently close to the true coefficient values to validate this method as an approach for generating quantum circuits. There is scope for more work in scaling this approach for larger quantum systems.
Wang, Hong-Fu; Zhu, Ai-Dong; Zhang, Shou
2013-05-20
We propose an efficient protocol for optimizing the physical implementation of three-qubit quantum error correction with spatially separated quantum dot spins via virtual-photon-induced process. In the protocol, each quantum dot is trapped in an individual cavity and each two cavities are connected by an optical fiber. We propose the optimal quantum circuits and describe the physical implementation for correcting both the bit flip and phase flip errors by applying a series of one-bit unitary rotation gates and two-bit quantum iSWAP gates that are produced by the long-range interaction between two distributed quantum dot spins mediated by the vacuum fields of the fiber and cavity. The protocol opens promising perspectives for long distance quantum communication and distributed quantum computation networks.
Simulating Special but Natural Quantum Circuits
Lipton, Richard J; Rudra, Atri
2012-01-01
We identify a sub-class of BQP that captures certain structural commonalities among many quantum algorithms including Shor's algorithms. This class does not contain all of BQP (e.g. Grover's algorithm does not fall into this class). Our main result is that any algorithm in this class that measures at most O(log n) qubits can be simulated by classical randomized polynomial time algorithms. This does not dequantize Shor's algorithm (as the latter measures n qubits) but our work also highlights a new potentially hard function for cryptographic applications. Our main technical contribution is (to the best of our knowledge) a new exact characterization of certain sums of Fourier-type coefficients (with exponentially many summands).
Efficient quantum circuits for one-way quantum computing.
Tanamoto, Tetsufumi; Liu, Yu-Xi; Hu, Xuedong; Nori, Franco
2009-03-13
While Ising-type interactions are ideal for implementing controlled phase flip gates in one-way quantum computing, natural interactions between solid-state qubits are most often described by either the XY or the Heisenberg models. We show an efficient way of generating cluster states directly using either the imaginary SWAP (iSWAP) gate for the XY model, or the sqrt[SWAP] gate for the Heisenberg model. Our approach thus makes one-way quantum computing more feasible for solid-state devices.
Quantum well intermixing for photonic integrated circuits
Sun, Xiaolan
2007-12-01
In this thesis, several aspects of GaAsSb/AlSb multiple quantum well (MQW) heterostructures have been studied. First, it was shown that the GaAsSb MQWs with a direct band gap near 1.5 mum at room temperature could be monolithically integrated with AlGaSb/AlSb or AlGaAsSb/AlAsSb Bragg mirrors, which can be applied to Vertical Cavity Surface Emitting Lasers (VCSELs). Secondly, an enhanced photoluminescence from GaAsSb MQWs was reported. The photoluminescence strength increased dramatically with arsenic fraction as conjectured. The peak photoluminescence from GaAs0.31Sb 0.69 was 208 times larger than that from GaSb. Thirdly, the strong photoluminescence from GaAsSb MQWs and the direct nature of the band gap near 1.5 mum at room temperature make the material favorable for intermixing studies. The samples were treated with ion implantation followed by rapid thermal annealing (RTA). A band gap blueshift as large as 198 nm was achieved with a modest ion dose and moderate annealing temperature. Photoluminescence strength for implanted samples generally increased with the annealing temperature. The energy blueshift was attributed to the interdiffusion of both the group III and group V sublattices. Finally, based on the interesting properties of GaAsSb MQWs, including the direct band gap near 1.5 mum, strong photoluminescence, a wide range of wavelength (1300--1500 nm) due to ion implantation-induced quantum well intermixing (QWI), and subpicosecond spin relaxation reported by Hall et al, we proposed to explore the possibilities for ultra-fast optical switching by investigating spin dynamics in semiconductor optical amplifiers (SOAs) containing InGaAs and GaSb MQWs. For circularly polarized pump and probe waves, the numerical simulation on the modal indices showed that the difference between the effective refractive index of the TE and TM modes was quite large, on the order of 0.03, resulting in a significant phase mismatch in a traveling length larger than 28 mum. Thus the
Evolution of Quantum State for Mesoscopic Circuits with Dissipation
Institute of Scientific and Technical Information of China (English)
WAN Hua-Ming; LUO Hai-Mei; WANG Yi-Fan
2005-01-01
Based on the maximum entropy principle, we present a density matrix of mesoscopic RLC circuit to make it possible to analyze the connection of the initial condition with temperature. Our results show that the quantum state evolution is closely related to the initial condition, and that the system evolves to generalized coherent state if it is in ground state initially, and evolves to squeezed state if it is in excited state initially.
Tomonaga-Luttinger physics in electronic quantum circuits.
Jezouin, S; Albert, M; Parmentier, F D; Anthore, A; Gennser, U; Cavanna, A; Safi, I; Pierre, F
2013-01-01
In one-dimensional conductors, interactions result in correlated electronic systems. At low energy, a hallmark signature of the so-called Tomonaga-Luttinger liquids is the universal conductance curve predicted in presence of an impurity. A seemingly different topic is the quantum laws of electricity, when distinct quantum conductors are assembled in a circuit. In particular, the conductances are suppressed at low energy, a phenomenon called dynamical Coulomb blockade. Here we investigate the conductance of mesoscopic circuits constituted by a short single-channel quantum conductor in series with a resistance, and demonstrate a proposed link to Tomonaga-Luttinger physics. We reformulate and establish experimentally a recently derived phenomenological expression for the conductance using a wide range of circuits, including carbon nanotube data obtained elsewhere. By confronting both conductance data and phenomenological expression with the universal Tomonaga-Luttinger conductance curve, we demonstrate experimentally the predicted mapping between dynamical Coulomb blockade and the transport across a Tomonaga-Luttinger liquid with an impurity.
Oscillatory localization of quantum walks analyzed by classical electric circuits
Ambainis, Andris; PrÅ«sis, KrišjÄnis; Vihrovs, JevgÄ`nijs; Wong, Thomas G.
2016-12-01
We examine an unexplored quantum phenomenon we call oscillatory localization, where a discrete-time quantum walk with Grover's diffusion coin jumps back and forth between two vertices. We then connect it to the power dissipation of a related electric network. Namely, we show that there are only two kinds of oscillating states, called uniform states and flip states, and that the projection of an arbitrary state onto a flip state is bounded by the power dissipation of an electric circuit. By applying this framework to states along a single edge of a graph, we show that low effective resistance implies oscillatory localization of the quantum walk. This reveals that oscillatory localization occurs on a large variety of regular graphs, including edge-transitive, expander, and high-degree graphs. As a corollary, high edge connectivity also implies localization of these states, since it is closely related to electric resistance.
A scanning transmon qubit for strong coupling circuit quantum electrodynamics.
Shanks, W E; Underwood, D L; Houck, A A
2013-01-01
Like a quantum computer designed for a particular class of problems, a quantum simulator enables quantitative modelling of quantum systems that is computationally intractable with a classical computer. Superconducting circuits have recently been investigated as an alternative system in which microwave photons confined to a lattice of coupled resonators act as the particles under study, with qubits coupled to the resonators producing effective photon-photon interactions. Such a system promises insight into the non-equilibrium physics of interacting bosons, but new tools are needed to understand this complex behaviour. Here we demonstrate the operation of a scanning transmon qubit and propose its use as a local probe of photon number within a superconducting resonator lattice. We map the coupling strength of the qubit to a resonator on a separate chip and show that the system reaches the strong coupling regime over a wide scanning area.
Institute of Scientific and Technical Information of China (English)
Hu Xiao-Mian; Liu Jin-Ming
2009-01-01
Quantum teleportation via the entangled channel composed of a two-qubit Heisenberg XYZ model with Dzyaloshinski-Moriya (DM) interaction in the presence of intrinsic decoherenee has been investigated. We find that the initial state of the channel plays an important role in the teleported state and the average fidelity of teleportation. When the initial channel is in the state [ψ1(0)>=a|00> + b|11>, the average fidelity is equal to 1/3 constantly, which is independent of the DM interaction and the intrinsic decoherence effect. But when the channel is initially in the state [ψ2(0)> = c|01) + d|10>, the average fidelity is always larger than 2/3. Moreover, under a certain condition, the average fidelity can be enhanced by adjusting the DM interaction, and the intrinsic decoherence leads to a suppression of the fluctuation of the average fidelity.
Implementing phase-covariant cloning in circuit quantum electrodynamics
Energy Technology Data Exchange (ETDEWEB)
Zhu, Meng-Zheng [School of Physics and Material Science, Anhui University, Hefei 230039 (China); School of Physics and Electronic Information, Huaibei Normal University, Huaibei 235000 (China); Ye, Liu, E-mail: yeliu@ahu.edu.cn [School of Physics and Material Science, Anhui University, Hefei 230039 (China)
2016-10-15
An efficient scheme is proposed to implement phase-covariant quantum cloning by using a superconducting transmon qubit coupled to a microwave cavity resonator in the strong dispersive limit of circuit quantum electrodynamics (QED). By solving the master equation numerically, we plot the Wigner function and Poisson distribution of the cavity mode after each operation in the cloning transformation sequence according to two logic circuits proposed. The visualizations of the quasi-probability distribution in phase-space for the cavity mode and the occupation probability distribution in the Fock basis enable us to penetrate the evolution process of cavity mode during the phase-covariant cloning (PCC) transformation. With the help of numerical simulation method, we find out that the present cloning machine is not the isotropic model because its output fidelity depends on the polar angle and the azimuthal angle of the initial input state on the Bloch sphere. The fidelity for the actual output clone of the present scheme is slightly smaller than one in the theoretical case. The simulation results are consistent with the theoretical ones. This further corroborates our scheme based on circuit QED can implement efficiently PCC transformation.
Implementing phase-covariant cloning in circuit quantum electrodynamics
Zhu, Meng-Zheng; Ye, Liu
2016-10-01
An efficient scheme is proposed to implement phase-covariant quantum cloning by using a superconducting transmon qubit coupled to a microwave cavity resonator in the strong dispersive limit of circuit quantum electrodynamics (QED). By solving the master equation numerically, we plot the Wigner function and Poisson distribution of the cavity mode after each operation in the cloning transformation sequence according to two logic circuits proposed. The visualizations of the quasi-probability distribution in phase-space for the cavity mode and the occupation probability distribution in the Fock basis enable us to penetrate the evolution process of cavity mode during the phase-covariant cloning (PCC) transformation. With the help of numerical simulation method, we find out that the present cloning machine is not the isotropic model because its output fidelity depends on the polar angle and the azimuthal angle of the initial input state on the Bloch sphere. The fidelity for the actual output clone of the present scheme is slightly smaller than one in the theoretical case. The simulation results are consistent with the theoretical ones. This further corroborates our scheme based on circuit QED can implement efficiently PCC transformation.
Photodetection of propagating quantum microwaves in circuit QED
Energy Technology Data Exchange (ETDEWEB)
Romero, Guillermo [Departamento de Fisica, Universidad de Santiago de Chile, USACH, Casilla 307, Santiago 2 (Chile); Garcia-Ripoll, Juan Jose [Instituto de Fisica Fundamental, CSIC, Serrano 113-bis, 28006 Madrid (Spain); Solano, Enrique [Departamento de Quimica Fisica, Universidad del PaIs Vasco - Euskal Herriko Unibertsitatea, Apdo. 644, 48080 Bilbao (Spain)], E-mail: enrique_solano@ehu.es
2009-12-15
We develop the theory of a metamaterial composed of an array of discrete quantum absorbers inside a one-dimensional waveguide that implements a high-efficiency microwave photon detector. A basic design consists of a few metastable superconducting nanocircuits spread inside and coupled to a one-dimensional waveguide in a circuit QED setup. The arrival of a propagating quantum microwave field induces an irreversible change in the population of the internal levels of the absorbers, due to a selective absorption of photon excitations. This design is studied using a formal but simple quantum field theory, which allows us to evaluate the single-photon absorption efficiency for one and many absorber setups. As an example, we consider a particular design that combines a coplanar coaxial waveguide with superconducting phase qubits, a natural but not exclusive playground for experimental implementations. This work and a possible experimental realization may stimulate the possible arrival of 'all-optical' quantum information processing with propagating quantum microwaves, where a microwave photodetector could play a key role.
Entanglement and entropy engineering of atomic two-qubit states
Clark, S G
2002-01-01
We propose a scheme employing quantum-reservoir engineering to controllably entangle the internal states of two atoms trapped in a high finesse optical cavity. Using laser and cavity fields to drive two separate Raman transitions between metastable atomic ground states, a system is realized corresponding to a pair of two-state atoms coupled collectively to a squeezed reservoir. Phase-sensitive reservoir correlations lead to entanglement between the atoms, and, via local unitary transformations and adjustment of the degree and purity of squeezing, one can prepare entangled mixed states with any allowed combination of linear entropy and entanglement of formation.
Ensembles of physical states and random quantum circuits on graphs
Hamma, Alioscia; Zanardi, Paolo
2012-01-01
In this paper we continue and extend the investigations of the ensembles of random physical states introduced in A. Hamma et al arXiv:1109.4391. These ensembles are constructed by finite-length random quantum circuits (RQC) acting on (hyper)edges of an underlying (hyper)graph structure. The latter encodes for the locality structure associated with finite-time quantum evolutions generated by physical i.e., local, Hamiltonians. Our goal is to analyze physical properties of typical states in these ensembles, in particular here we focus on proxies of quantum entanglement as purity and $\\alpha$-Renyi entropies. The problem is formulated in terms of matrix elements of superoperators which depend on the graph structure, choice of probability measure over the local unitaries and circuit length. In the $\\alpha=2$ case these superoperators act on a restricted multi-qubit space generated by permutation operators associated to the subsets of vertices of the graph. For permutationally invariant interactions the dynamics c...
Rabi model as a quantum coherent heat engine: From quantum biology to superconducting circuits
2014-01-01
PHYSICAL REVIEW A 91, 023816 (2015) Rabi model as a quantum coherent heat engine: From quantum biology to superconducting circuits Ferdi Altintas,1 Ali U¨ . C. Hardal,2 and O¨ zgu¨r E. Mu¨stecaplıog˘lu2,* 1Department of Physics, Abant Izzet Baysal University, Bolu, 14280, Turkey 2Department of Physics, Koc¸ University, Sarıyer, ˙Istanbul, 34450, Turkey (Received 10 November 2014; published 12 February 2015) We propose a multilevel quantum heat engine with a working medium de...
Rabi model as a quantum coherent heat engine: From quantum biology to superconducting circuits
Altintas, Ferdi; Hardal, Ali Ü. C.; Müstecaplıoǧlu, Özgür E.
2015-02-01
We propose a multilevel quantum heat engine with a working medium described by a generalized Rabi model which consists of a two-level system coupled to a single-mode bosonic field. The model is constructed to be a continuum limit of a quantum biological description of light-harvesting complexes so that it can amplify quantum coherence by a mechanism which is a quantum analog of classical Huygens clocks. The engine operates in a quantum Otto cycle where the working medium is coupled to classical heat baths in the isochoric processes of the four-stroke cycle, while either the coupling strength or the resonance frequency is changed in the adiabatic stages. We found that such an engine can produce work with an efficiency close to the Carnot bound when it operates at low temperatures and in the ultrastrong-coupling regime. The interplay of the effects of quantum coherence and quantum correlations on the engine performance is discussed in terms of second-order coherence, quantum mutual information, and the logarithmic negativity of entanglement. We point out that the proposed quantum Otto engine can be implemented experimentally with modern circuit quantum electrodynamic systems where flux qubits can be coupled ultrastrongly to superconducting transmission-line resonators.
Single-photon transistor in circuit quantum electrodynamics.
Neumeier, Lukas; Leib, Martin; Hartmann, Michael J
2013-08-01
We introduce a circuit quantum electrodynamical setup for a "single-photon" transistor. In our approach photons propagate in two open transmission lines that are coupled via two interacting transmon qubits. The interaction is such that no photons are exchanged between the two transmission lines but a single photon in one line can completely block or enable the propagation of photons in the other line. High on-off ratios can be achieved for feasible experimental parameters. Our approach is inherently scalable as all photon pulses can have the same pulse shape and carrier frequency such that output signals of one transistor can be input signals for a consecutive transistor.
Controlling group velocity in a superconductive quantum circuit
Institute of Scientific and Technical Information of China (English)
Qiu Tian-Hui; Yang Guo-Jian
2012-01-01
We investigate the controllable group velocity of a microwave probe field in a superconductive quantum circuit (SQC) pumped by microwave fields,and the use of such a SQC function as an artificial A-type three-level atom.The exchange between the subluminal and the superluminal states of the probe field can be realized simply by sweeping the pumping intensity,and the superluminal state is usually realized with a lower absorption.This work is one of the efforts to extend the study of electromagnetically induced transparency and its related properties from the lightwave band to the microwave band.
Experiments on two-resonator circuit quantum electrodynamics. A superconducting quantum switch
Energy Technology Data Exchange (ETDEWEB)
Hoffmann, Elisabeth Christiane Maria
2013-05-29
The field of cavity quantum electrodynamics (QED) studies the interaction between light and matter on a fundamental level. In typical experiments individual natural atoms are interacting with individual photons trapped in three-dimensional cavities. Within the last decade the prospering new field of circuit QED has been developed. Here, the natural atoms are replaced by artificial solid state quantum circuits offering large dipole moments which are coupled to quasi-onedimensional cavities providing a small mode volume and hence a large vacuum field strength. In our experiments Josephson junction based superconducting quantum bits are coupled to superconducting microwave resonators. In circuit QED the number of parameters that can be varied is increased and regimes that are not accessible using natural atoms can be entered and investigated. Apart from design flexibility and tunability of system parameters a particular advantage of circuit QED is the scalability to larger system size enabled by well developed micro- and nanofabrication tools. When scaling up the resonator-qubit systems beyond a few coupled circuits, the rapidly increasing number of interacting subsystems requires an active control and directed transmission of quantum signals. This can, for example, be achieved by implementing switchable coupling between two microwave resonators. To this end, a superconducting flux qubit is used to realize a suitable coupling between two microwave resonators, all working in the Gigahertz regime. The resulting device is called quantum switch. The flux qubit mediates a second order tunable and switchable coupling between the resonators. Depending on the qubit state, this coupling can compensate for the direct geometric coupling of the two resonators. As the qubit may also be in a quantum superposition state, the switch itself can be ''quantum'': it can be a superposition of ''on'' and ''off''. This work
Entangling capabilities of symmetric two-qubit gates
Indian Academy of Sciences (India)
Swarnamala Sirsi; Veena Adiga; Subramanya Hegde
2014-08-01
Our work addresses the problem of generating maximally entangled two spin-1/2 (qubit) symmetric states using NMR, NQR, Lipkin–Meshkov–Glick Hamiltonians. Time evolution of such Hamiltonians provides various logic gates which can be used for quantum processing tasks. Pairs of spin-1/2s have modelled a wide range of problems in physics. Here, we are interested in two spin-1/2 symmetric states which belong to a subspace spanned by the angular momentum basis $\\{|j = 1,\\langle; = + 1, 0, -12\\}$. Our technique relies on the decomposition of a Hamiltonian in terms of (3) basis matrices. In this context, we define a set of linearly independent, traceless, Hermitian operators which provides an alternate set of () generators. These matrices are constructed out of angular momentum operators J$_x$, J$_y$, J$_z$. We construct and study the properties of perfect entanglers acting on a symmetric subspace, i.e., spin-1 operators that can generate maximally entangled states from some suitably chosen initial separable states in terms of their entangling power.
A geometric theory of non-local two-qubit operations
Zhang, J; Whaley, K B; Sastry, S; Zhang, Jun; Vala, Jiri; Sastry, Shankar
2003-01-01
We study non-local two-qubit operations from a geometric perspective. By applying a Cartan decomposition to su(4), we find that the geometric structure of non-local gates is a 3-Torus. We derive the invariants for local transformations, and connect these local invariants to the coordinates of the 3-Torus. Since different points on the 3-Torus may correspond to the same local equivalence class, we use the Weyl group theory to reduce the symmetry. We show that the local equivalence classes of two-qubit gates are in one-to-one correspondence with the points in a tetrahedron except on the base. We then study the properties of perfect entanglers, that is, the two-qubit operations that can generate maximally entangled states from some initially separable states. We provide criteria to determine whether a given two-qubit gate is a perfect entangler and establish a geometric description of perfect entanglers by making use of the tetrahedral representation of non-local gates. We find that exactly half the non-local ga...
Entanglement capacity of two-qubit unitary operator for rank two mixed states
Institute of Scientific and Technical Information of China (English)
DI; YaoMin
2007-01-01
The entanglement capacity of two-qubit unitary operator acting on rank two mixed states in concurrence is discussed. The condition of perfect entangler is the same as that acting on pure states and the entanglement capacity is the mixing parameter v1. For non-perfect entangler, the upper and lower bound of the entanglement capacity are given.……
Measurement-induced two-qubit entanglement in a bad cavity: Fundamental and practical considerations
DEFF Research Database (Denmark)
Julsgaard, Brian; Mølmer, Klaus
2012-01-01
An entanglement-generating protocol is described for two qubits coupled to a cavity field in the bad-cavity limit. By measuring the amplitude of a field transmitted through the cavity, an entangled spin-singlet state can be established probabilistically. Both fundamental limitations and practical...
Entanglement capacity of two-qubit unitary operator for rank two mixed states
Institute of Scientific and Technical Information of China (English)
无
2007-01-01
@@ The entanglement capacity of two-qubit unitary operator acting on rank two mixed states in concurrence is discussed. The condition of perfect entangler is the same as that acting on pure states and the entanglement capacity is the mixing parameter v1. For non-perfect entangler, the upper and lower bound of the entanglement capacity are given.
Constructing quantum circuits for maximally entangled multi-qubit states using the genetic algorithm
Fan, Zheyong; Goertzel, Ben; Ren, Zhongzhou; Zeng, Huabi
2010-01-01
Numerical optimization methods such as hillclimbing and simulated annealing have been applied to search for highly entangled multi-qubit states. Here the genetic algorithm is applied to this optimization problem -- to search not only for highly entangled states, but also for the corresponding quantum circuits creating these states. Simple quantum circuits for maximally (highly) entangled states are discovered for 3, 4, 5, and 6-qubit systems; and extension of the method to systems with more qubits is discussed. Among other results we have found explicit quantum circuits for maximally entangled 5 and 6-qubit circuits, with only 8 and 13 quantum gates respectively. One significant advantage of our method over previous ones is that it allows very simple construction of quantum circuits based on the quantum states found.
Controlled Remote State Preparation of an Arbitrary Two-Qubit State via a Six-Qubit Cluster State
Sang, Ming-huang; Nie, Li-ping
2017-07-01
In this work, we have demonstrated that a six-qubit cluster state can be used to realize the deterministic controlled remote state preparation of an arbitrary two-qubit state by performing only the special two-qubit projective measurements.
Iemini, Fernando; da Silva Souza, Leonardo; Debarba, Tiago; Cesário, André T.; Maciel, Thiago O.; Vianna, Reinaldo O.
2017-05-01
We obtain the analytical expression for the Kraus decomposition of the quantum map of an environment modeled by an arbitrary quadratic fermionic Hamiltonian acting on one or two qubits, and derive simple functions to check the non-positivity of the intermediate map. These functions correspond to two different sufficient criteria for non-Markovianity. In the particular case of an environment represented by the Ising Hamiltonian, we discuss the two sources of non-Markovianity in the model, one due to the finite size of the lattice, and another due to the kind of interactions.
Superposition states for quantum nanoelectronic circuits and their nonclassical properties
Choi, Jeong Ryeol
2016-09-01
Quantum properties of a superposition state for a series RLC nanoelectronic circuit are investigated. Two displaced number states of the same amplitude but with opposite phases are considered as components of the superposition state. We have assumed that the capacitance of the system varies with time and a time-dependent power source is exerted on the system. The effects of displacement and a sinusoidal power source on the characteristics of the state are addressed in detail. Depending on the magnitude of the sinusoidal power source, the wave packets that propagate in charge(q)-space are more or less distorted. Provided that the displacement is sufficiently high, distinct interference structures appear in the plot of the time behavior of the probability density whenever the two components of the wave packet meet together. This is strong evidence for the advent of nonclassical properties in the system, that cannot be interpretable by the classical theory. Nonclassicality of a quantum system is not only a beneficial topic for academic interest in itself, but its results can be useful resources for quantum information and computation as well.
Quantum circuits and low-degree polynomials over {{{F}}_\\mathsf{2}}
Montanaro, Ashley
2017-02-01
In this work we explore a correspondence between quantum circuits and low-degree polynomials over the finite field {{{F}}2} . Any quantum circuit made up of Hadamard, Z, controlled-Z and controlled-controlled-Z gates gives rise to a degree-3 polynomial over {{{F}}2} such that calculating quantum circuit amplitudes is equivalent to counting zeroes of the corresponding polynomial. We exploit this connection, which is especially clean and simple for this particular gate set, in two directions. First, we give proofs of classical hardness results based on quantum circuit concepts. Second, we find efficient classical simulation algorithms for certain classes of quantum circuits based on efficient algorithms for classes of polynomials.
Design of arithmetic circuits in quantum dot cellular automata nanotechnology
Sridharan, K
2015-01-01
This research monograph focuses on the design of arithmetic circuits in Quantum Dot Cellular Automata (QCA). Using the fact that the 3-input majority gate is a primitive in QCA, the book sets out to discover hitherto unknown properties of majority logic in the context of arithmetic circuit designs. The pursuit for efficient adders in QCA takes two forms. One involves application of the new results in majority logic to existing adders. The second involves development of a custom adder for QCA technology. A QCA adder named as hybrid adder is proposed and it is shown that it outperforms existing multi-bit adders with respect to area and delay. The work is extended to the design of a low-complexity multiplier for signed numbers in QCA. Furthermore the book explores two aspects unique to QCA technology, namely thermal robustness and the role of interconnects. In addition, the book introduces the reader to QCA layout design and simulation using QCADesigner. Features & Benefits: This research-based book: · �...
Phase-controlled coherent population trapping in superconducting quantum circuits
Institute of Scientific and Technical Information of China (English)
程广玲; 王一平; 陈爱喜
2015-01-01
We investigate the influences of the-applied-field phases and amplitudes on the coherent population trapping behavior in superconducting quantum circuits. Based on the interactions of the microwave fields with a single∆-type three-level fluxonium qubit, the coherent population trapping could be obtainable and it is very sensitive to the relative phase and amplitudes of the applied fields. When the relative phase is tuned to 0 orπ, the maximal atomic coherence is present and coherent population trapping occurs. While for the choice ofπ/2, the atomic coherence becomes weak. Meanwhile, for the fixed relative phaseπ/2, the value of coherence would decrease with the increase of Rabi frequency of the external field coupled with two lower levels. The responsible physical mechanism is quantum interference induced by the control fields, which is indicated in the dressed-state representation. The microwave coherent phenomenon is present in our scheme, which will have potential applications in optical communication and nonlinear optics in solid-state devices.
Relative entropy of entanglement of two-qubit Ux-invariant states
Wang, Zhen; Wang, Zhi-Xi
2015-01-01
It is strictly proved that a two-qubit Ux-invariant state reaches its relative entropy of entanglement (REE) by the separable state having the same matrix structure. We also formulate three quadratic equations for the corresponding closest separable state (CSS) of Ux-invariant states by their symmetric property. Thus, the CSS of Ux-invariant state can be provided. Furthermore, to illustrate our result we consider two concrete examples.
Simple Scheme for Directly Measuring Concurrence of Two-Qubit Pure States in One Step
Institute of Scientific and Technical Information of China (English)
YANG Rong-Can; LIN Xiu; HUANG Zhi-Ping; LI Hong-Cai
2009-01-01
In the present work, a simple scheme for the direct measurement of the concurrence of two-qubit pure states is proposed.The scheme is based on trapped ions and only needs one step when the two identical pure states are given.The vibrational mode in our proposal is only virtually excited, which is important in view of decoherence.Furthermore, the scheme is feasible based on current technologies.
Bipartite entanglement in a two-qubit Heisenberg XXZ chain under an inhomogeneous magnetic field
Institute of Scientific and Technical Information of China (English)
QIN Meng; TIAN Dong-Ping
2009-01-01
This paper investigates the bipartite entanglement of a two-qubit Heisenberg XXZ chain under an inhomogeneous magnetic field. By the concept of negativity, we find that the inhomogeneity of the magnetic field may induce entanglement and the critical magnetic field is independent of Jz. We also find that the entanglement is symmetric with respect to a zero magnetic field. The anisotropy parameter Jz may enhance the entanglement.
Efficient quantum circuits for continuous-time quantum walks on composite graphs
Loke, T.; Wang, J. B.
2017-02-01
In this paper, we investigate the simulation of continuous-time quantum walks on specific classes of graphs, for which it is possible to fast-forward the time-evolution operator to achieve constant-time simulation complexity and to perform the simulation exactly, i.e. ε =0 , while maintaining \\text{poly}≤ft(\\text{log}(n)\\right) efficiency. In particular, we discuss two classes of composite graphs, commuting graphs and Cartesian product of graphs, that contain classes of graphs which can be simulated in this fashion. This allows us to identify new families of graphs that we can efficiently simulate in a quantum circuit framework, providing practical and explicit means to explore quantum-walk based algorithms in laboratories.
The Scalable Integration of long-lived quantum memories into a photonic circuit
Mouradian, Sara L; Poitras, Carl B; Li, Luozhou; Goldstein, Jordan; Chen, Edward H; Cardenas, Jaime; Markham, Matthew L; Twitchen, Daniel J; Lipson, Michal; Englund, Dirk
2014-01-01
We demonstrate a photonic circuit with integrated long-lived quantum memories. Pre-selected quantum nodes - diamond micro-waveguides containing single, stable, and negatively charged nitrogen vacancy centers - are deterministically integrated into low-loss silicon nitride waveguides. Each quantum memory node efficiently couples into the single-mode waveguide (> 1 Mcps collected into the waveguide) and exhibits long spin coherence times of up to 120 {\\mu}s. Our system facilitates the assembly of multiple quantum memories into a photonic integrated circuit with near unity yield, paving the way towards scalable quantum information processing.
Quantum State Transfer between Charge and Flux Qubits in Circuit-QED
Institute of Scientific and Technical Information of China (English)
WU Qin-Qin; LIAO Jie-Qiao; KUANG Le-Man
2008-01-01
@@ We propose a scheme to implement quantum state transfer in a hybrid circuit quantum electrodynamics (QED)system which consists of a superconducting charge qubit, a flux qubit, and a transmission line resonator (TLR).It is shown that quantum state transfer between the charge qubit and the flux qubit can be realized by using the TLR as the data bus.
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.
Deterministic quantum teleportation with feed-forward in a solid state system.
Steffen, L; Salathe, Y; Oppliger, M; Kurpiers, P; Baur, M; Lang, C; Eichler, C; Puebla-Hellmann, G; Fedorov, A; Wallraff, A
2013-08-15
Engineered macroscopic quantum systems based on superconducting electronic circuits are attractive for experimentally exploring diverse questions in quantum information science. At the current state of the art, quantum bits (qubits) are fabricated, initialized, controlled, read out and coupled to each other in simple circuits. This enables the realization of basic logic gates, the creation of complex entangled states and the demonstration of algorithms or error correction. Using different variants of low-noise parametric amplifiers, dispersive quantum non-demolition single-shot readout of single-qubit states with high fidelity has enabled continuous and discrete feedback control of single qubits. Here we realize full deterministic quantum teleportation with feed-forward in a chip-based superconducting circuit architecture. We use a set of two parametric amplifiers for both joint two-qubit and individual qubit single-shot readout, combined with flexible real-time digital electronics. Our device uses a crossed quantum bus technology that allows us to create complex networks with arbitrary connecting topology in a planar architecture. The deterministic teleportation process succeeds with order unit probability for any input state, as we prepare maximally entangled two-qubit states as a resource and distinguish all Bell states in a single two-qubit measurement with high efficiency and high fidelity. We teleport quantum states between two macroscopic systems separated by 6 mm at a rate of 10(4) s(-1), exceeding other reported implementations. The low transmission loss of superconducting waveguides is likely to enable the range of this and other schemes to be extended to significantly larger distances, enabling tests of non-locality and the realization of elements for quantum communication at microwave frequencies. The demonstrated feed-forward may also find application in error correction schemes.
Distributed quantum computation with superconducting qubit via LC circuit using dressed states
Institute of Scientific and Technical Information of China (English)
Wu Chao; Fang Mao-Fa; Xiao Xing; Li Yan-Ling; Cao Shuai
2011-01-01
A scheme is proposed where two superconducting qubits driven by a classical field interacting separately with two distant LC circuits connected by another LC circuit through mutual inductance, are used for implementing quantum gates. By using dressed states, quantum state transfer and quantum entangling gate can be implemented. With the help of the time-dependent electromagnetic field, any two dressed qubits can be selectively coupled to the data bus (the last LC circuit), then quantum state can be transferred from one dressed qubit to another and multi-mode entangled state can also be formed. As a result, the promising perspectives for quantum information processing of mesoscopic superconducting qubits are obtained and the distributed and scalable quantum computation can be implemented in this scheme.
Quantum Bayesian rule for weak measurements of qubits in superconducting circuit QED
Wang, Peiyue; Qin, Lupei; Li, Xin-Qi
2014-01-01
Compared with the quantum trajectory equation, the quantum Bayesian approach has the advantage of being more efficient to infer quantum state under monitoring, based on the integrated output of measurement. For weak measurement of qubits in circuit quantum electrodynamics(cQED), properly accounting for the measurement backaction effects within the Bayesian framework is an important problem of current interest.Elegant work towards this task was carried out by Korotkov in "bad-cavity" and weak-...
Dynamical Lamb effect versus dissipation in superconducting quantum circuits
Zhukov, A. A.; Shapiro, D. S.; Pogosov, W. V.; Lozovik, Yu. E.
2016-06-01
Superconducting circuits provide a new platform for study of nonstationary cavity QED phenomena. An example of such a phenomenon is the dynamical Lamb effect, which is the parametric excitation of an atom due to nonadiabatic modulation of its Lamb shift. This effect was initially introduced for a natural atom in a varying cavity, while we suggest its realization in a superconducting qubit-cavity system with dynamically tunable coupling. In the present paper, we study the interplay between the dynamical Lamb effect and the energy dissipation, which is unavoidable in realistic systems. We find that despite naive expectations, this interplay can lead to unexpected dynamical regimes. One of the most striking results is that photon generation from vacuum can be strongly enhanced due to qubit relaxation, which opens another channel for such a process. We also show that dissipation in the cavity can increase the qubit excited-state population. Our results can be used for experimental observation and investigation of the dynamical Lamb effect and accompanying quantum effects.
Quantum Fluctuation of a Mesoscopic Inductance Coupling Circuit at Finite Temperature
Institute of Scientific and Technical Information of China (English)
SONG Tong-Qiang; ZHU Yue-Jin
2003-01-01
We study the quantization of mesoscopic inductance coupling circuit and discuss its time evolution. Bymeans of the thermal field dynamics theory we study the quantum fluctuation of the system at finite temperature.
Fully integrated quantum photonic circuit with an electrically driven light source
Khasminskaya, Svetlana; Pyatkov, Felix; Słowik, Karolina; Ferrari, Simone; Kahl, Oliver; Kovalyuk, Vadim; Rath, Patrik; Vetter, Andreas; Hennrich, Frank; Kappes, Manfred M.; Gol'Tsman, G.; Korneev, A.; Rockstuhl, Carsten; Krupke, Ralph; Pernice, Wolfram H. P.
2016-11-01
Photonic quantum technologies allow quantum phenomena to be exploited in applications such as quantum cryptography, quantum simulation and quantum computation. A key requirement for practical devices is the scalable integration of single-photon sources, detectors and linear optical elements on a common platform. Nanophotonic circuits enable the realization of complex linear optical systems, while non-classical light can be measured with waveguide-integrated detectors. However, reproducible single-photon sources with high brightness and compatibility with photonic devices remain elusive for fully integrated systems. Here, we report the observation of antibunching in the light emitted from an electrically driven carbon nanotube embedded within a photonic quantum circuit. Non-classical light generated on chip is recorded under cryogenic conditions with waveguide-integrated superconducting single-photon detectors, without requiring optical filtering. Because exclusively scalable fabrication and deposition methods are used, our results establish carbon nanotubes as promising nanoscale single-photon emitters for hybrid quantum photonic devices.
Patel, Raj B; Ho, Joseph; Ferreyrol, Franck; Ralph, Timothy C; Pryde, Geoff J
2016-03-01
Minimizing the resources required to build logic gates into useful processing circuits is key to realizing quantum computers. Although the salient features of a quantum computer have been shown in proof-of-principle experiments, difficulties in scaling quantum systems have made more complex operations intractable. This is exemplified in the classical Fredkin (controlled-SWAP) gate for which, despite theoretical proposals, no quantum analog has been realized. By adding control to the SWAP unitary, we use photonic qubit logic to demonstrate the first quantum Fredkin gate, which promises many applications in quantum information and measurement. We implement example algorithms and generate the highest-fidelity three-photon Greenberger-Horne-Zeilinger states to date. The technique we use allows one to add a control operation to a black-box unitary, something that is impossible in the standard circuit model. Our experiment represents the first use of this technique to control a two-qubit operation and paves the way for larger controlled circuits to be realized efficiently.
Bialczak, R C; Hofheinz, M; Lenander, M; Lucero, E; Neeley, M; O'Connell, A D; Sank, D; Wang, H; Weides, M; Wenner, J; Yamamoto, T; Cleland, A N; Martinis, J M
2010-01-01
A major challenge in the field of quantum computing is the construction of scalable qubit coupling architectures. Here, we demonstrate a novel tuneable coupling circuit that allows superconducting qubits to be coupled over long distances. We show that the inter-qubit coupling strength can be arbitrarily tuned over nanosecond timescales within a sequence that mimics actual use in an algorithm. The coupler has a measured on/off ratio of 1000. The design is self-contained and physically separate from the qubits, allowing the coupler to be used as a module to connect a variety of elements such as qubits, resonators, amplifiers, and readout circuitry over long distances. Such design flexibility is likely to be essential for a scalable quantum computer.
Flamini, Fulvio; Rab, Adil S; Spagnolo, Nicolò; D'Ambrosio, Vincenzo; Mataloni, Paolo; Sciarrino, Fabio; Zandrini, Tommaso; Crespi, Andrea; Ramponi, Roberta; Osellame, Roberto
2015-01-01
The importance of integrated quantum photonics in the telecom band resides on the possibility of interfacing with the optical network infrastructure developed for classical communications. In this framework, femtosecond laser written integrated photonic circuits, already assessed for quantum information experiments in the 800 nm wavelength range, have great potentials. In fact these circuits, written in glass, can be perfectly mode-matched at telecom wavelength to the in/out coupling fibers, which is a key requirement for a low-loss processing node in future quantum optical networks. In addition, for several applications quantum photonic devices will also need to be dynamically reconfigurable. Here we experimentally demonstrate the high performance of femtosecond laser written photonic circuits for quantum experiments in the telecom band and we show the use of thermal shifters, also fabricated by the same femtosecond laser, to accurately tune them. State-of-the-art manipulation of single and two-photon states...
Quantum Fluctuation in Thermal Vacuum State for Mesoscopic LC Electric Circuit
Institute of Scientific and Technical Information of China (English)
FAN Hong-Yi; LIANG Xian-Ting
2000-01-01
We consider the quantization of LC (inductance-capacitance) circuit at a finite temperature T as any practical circuits always produce Joule heat except for superconductivity. It is shown that the quantum mechanical zeropoint fluctuations of both charge and current increase with upgoing T. Thermal field dynamics is used in ourdiscussion.
Quantum Fluctuation in Mesoscopic Coupled LC Electric Circuits at FiniteTemperature
Institute of Scientific and Technical Information of China (English)
LIANG Xian-Ting; FAN Hong-Yi
2001-01-01
We consider the quantization of two coupled LC circuits with mutual inductance at a finite temperature T. It is shown that the quantum mechanical zero-point fluctuations of currents in the two circuits both increase with upgoing T. Thermal field dynamics and Weyl-Wigner theorern are used in our calculation of ensemble average of the observables.
Institute of Scientific and Technical Information of China (English)
Qin Meng; Tian Dong-Ping
2009-01-01
This paper investigates bipartite entanglement of a two-qubit system with anisotropic couplings under all inhomogeneous magnetic field.This work is mainly to investigate the characteristics of a Heisenberg XYZ chain and obtains some meaningful results.By the concept of negativity,it finds that the inhomogeneity of magnetic field may induce entanglement and the critical magnetic field is independent of Jz.The inhomogeneous magnetic field can increase the value of critical magnetic field Bc.It also finds that the magnetic field not only suppresses the entanglement but also can induce it to revival for some time.
Optimal feedback control of two-qubit entanglement in dissipative environments
Rafiee, Morteza; Nourmandipour, Alireza; Mancini, Stefano
2016-07-01
We study the correction of errors intervening in two qubits dissipating into their own environments. This is done by resorting to local feedback actions with the aim of preserving as much as possible the initial amount of entanglement. Optimal control is found first by gaining insights from the subsystem purity and then by numerical analysis on the concurrence. This is tantamount to a double optimization on the actuation and on the measurement processes. Repeated feedback action is also investigated, thus paving the way for a continuous-time formulation and a solution of the problem.
A study of two-qubit density matrices with fermionic purifications
Energy Technology Data Exchange (ETDEWEB)
Szalay, Szilard; Levay, Peter; Nagy, Szilvia; Pipek, Janos [Department of Theoretical Physics, Institute of Physics, Budapest University of Technology and Economics, H-1111 Budafoki ut 8 (Hungary)
2008-12-19
We study 12 parameter families of two-qubit density matrices, arising from a special class of two-fermion systems with four single-particle states or alternatively from a four-qubit state with amplitudes arranged in an antisymmetric matrix. We calculate the Wootters concurrences and the negativities in a closed form and study their behavior. We use these results to show that the relevant entanglement measures satisfy the generalized Coffman-Kundu-Wootters formula of distributed entanglement. An explicit formula for the residual tangle is also given. The geometry of such density matrices is elaborated in some detail. In particular, an explicit form for the Bures metric is given.
Entanglement Dynamics of Two-Qubit System in Different Types of Noisy Channels
Institute of Scientific and Technical Information of China (English)
SHAN Chuan-Jia; LIU Ji-Bing; CHENG Wei-Wen; LIU Tang-Kun; HUANG Yan-Xia; LI Hong
2009-01-01
In this paper, we study entanglement dynamics of a two-qubit extended Werner-like state locally interacting with independent noisy channels, i.e., amplitude damping, phase damping, and depolarizing channels. We show that the purity of initial entangled state has direct impacts on the entanglement robustness in each noisy channel. That is, if the initial entangled state is prepared in mixed instead of pure form, the state may exhibit entanglement sudden death (ESD) and/or be decreased for the critical probability at which the entanglement disappear.
Wei, Hai-Rui; Lu Long, Gui
2015-01-01
Hybrid quantum gates hold great promise for quantum information processing since they preserve the advantages of different quantum systems. Here we present compact quantum circuits to deterministically implement controlled-NOT, Toffoli, and Fredkin gates between a flying photon qubit and diamond nitrogen-vacancy (NV) centers assisted by microcavities. The target qubits of these universal quantum gates are encoded on the spins of the electrons associated with the diamond NV centers and they have long coherence time for storing information, and the control qubit is encoded on the polarizations of the flying photon and can be easily manipulated. Our quantum circuits are compact, economic, and simple. Moreover, they do not require additional qubits. The complexity of our schemes for universal three-qubit gates is much reduced, compared to the synthesis with two-qubit entangling gates. These schemes have high fidelities and efficiencies, and they are feasible in experiment. PMID:26271899
Energy Technology Data Exchange (ETDEWEB)
Chen, Jingwei [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Wei, L.F., E-mail: weilianfu@gmail.com [State Key Laboratory of Optoelectronic Materials and Technologies, School of Physics and Engineering, Sun Yat-sen University, Guangzhou 510275 (China); Quantum Optoelectronics Laboratory, School of Physics and Technology, Southwest Jiaotong University, Chengdu 610031 (China)
2015-10-23
Highlights: • A specific SCRAP technique is proposed to realize quantum gates in the circuit QED. • These quantum gates are insensitive to the durations of the applied pluses. • The implemented quantum gates are robustness against the operational imperfections. - Abstract: We show that a set of universal quantum gates could be implemented robustly in a circuit QED system by using Stark-chirped rapid adiabatic passage (SCRAP) technique. Under the adiabatic limit we find that the population transfers could be deterministically passaged from one selected quantum states to the others, and thus the desired quantum gates can be implemented. The proposed SCRAP-based gates are insensitive to the details of the operations and thus relax the designs of the applied pulses, operational imperfections, and the decoherence of the system.
A quantum watermarking scheme using simple and small-scale quantum circuits
Miyake, S.; Nakamae, K.
2016-05-01
A new quantum gray-scale image watermarking scheme by using simple and small-scale quantum circuits is proposed. The NEQR representation for quantum images is used. The image sizes for carrier and watermark are assumed to be 2n × 2n and n × n, respectively. At first, a classical watermark with n × n image size and 8 bits gray scale is expanded to an image with 2n × 2n image size and 2 bits gray scale. Then the expanded image is scrambled to be a meaningless image by the SWAP gates that controlled by the keys only known to the operator. The scrambled image is embedded into the carrier image by the CNOT gates (XOR operation). The watermark is extracted from the watermarked image by applying operations in the reverse order. Simulation-based experimental results show that our proposed scheme is excellent in terms of three items, visual quality, robustness performance under noises, and computational complexity.
Fermion-fermion scattering in quantum field theory with superconducting circuits.
García-Álvarez, L; Casanova, J; Mezzacapo, A; Egusquiza, I L; Lamata, L; Romero, G; Solano, E
2015-02-20
We propose an analog-digital quantum simulation of fermion-fermion scattering mediated by a continuum of bosonic modes within a circuit quantum electrodynamics scenario. This quantum technology naturally provides strong coupling of superconducting qubits with a continuum of electromagnetic modes in an open transmission line. In this way, we propose qubits to efficiently simulate fermionic modes via digital techniques, while we consider the continuum complexity of an open transmission line to simulate the continuum complexity of bosonic modes in quantum field theories. Therefore, we believe that the complexity-simulating-complexity concept should become a leading paradigm in any effort towards scalable quantum simulations.
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
Quantum secure direct communication over the collective amplitude damping channel
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
An efficient quantum secure direct communication protocol is presented over the amplitude damping channel.The protocol encodes logical bits in two-qubit noiseless states,and so it can function over a quantum channel subjected to collective amplitude damping.The feature of this protocol is that the sender encodes the secret directly on the quantum states,the receiver decodes the secret by performing determinate measurements,and there is no basis mismatch.The transmission’s safety is ensured by the nonorthogonality of the noiseless states traveling forward and backward on the quantum channel.Moreover,we construct the efficient quantum circuits to implement channel encoding and information encoding by means of primitive operations in quantum computation.
Quantum secure direct communication over the collective amplitude damping channel
Institute of Scientific and Technical Information of China (English)
QIN Suduan; WEN QiaoYan; MENG LuoMing; ZHU FuChen
2009-01-01
An efficient quantum secure direct communication protocol is presented over the amplitude damping channel. The protocol encodes logical bits in two-qubit noiseless states, and so it can function over a quantum channel subjected to collective amplitude damping. The feature of this protocol is that the sender encodes the secret directly on the quantum states, the receiver decodes the secret by per-forming determinate measurements, and there is no basis mismatch. The transmission's safely is en-sured by the nonorthogonality of the noiseless states traveling forward and backward on the quantum channel. Moreover, we construct the efficient quantum circuits to implement channel encoding and information enooding by means of primitive operations in quantum computation.
Geometric reduction of dynamical nonlocality in nanoscale quantum circuits
Strambini, E.; Makarenko, K.S.; Abulizi, G.; Jong, de M.P.; Wiel, van der W.G.
2016-01-01
Nonlocality is a key feature discriminating quantum and classical physics. Quantum-interference phenomena, such as Young’s double slit experiment, are one of the clearest manifestations of nonlocality, recently addressed as dynamical to specify its origin in the quantum equations of motion. It is we
Graphene-based room-temperature implementation of a modified Deutsch-Jozsa quantum algorithm.
Dragoman, Daniela; Dragoman, Mircea
2015-12-04
We present an implementation of a one-qubit and two-qubit modified Deutsch-Jozsa quantum algorithm based on graphene ballistic devices working at room temperature. The modified Deutsch-Jozsa algorithm decides whether a function, equivalent to the effect of an energy potential distribution on the wave function of ballistic charge carriers, is constant or not, without measuring the output wave function. The function need not be Boolean. Simulations confirm that the algorithm works properly, opening the way toward quantum computing at room temperature based on the same clean-room technologies as those used for fabrication of very-large-scale integrated circuits.
Preparation and measurement of three-qubit entanglement in a superconducting circuit.
Dicarlo, L; Reed, M D; Sun, L; Johnson, B R; Chow, J M; Gambetta, J M; Frunzio, L; Girvin, S M; Devoret, M H; Schoelkopf, R J
2010-09-30
Traditionally, quantum entanglement has been central to foundational discussions of quantum mechanics. The measurement of correlations between entangled particles can have results at odds with classical behaviour. These discrepancies grow exponentially with the number of entangled particles. With the ample experimental confirmation of quantum mechanical predictions, entanglement has evolved from a philosophical conundrum into a key resource for technologies such as quantum communication and computation. Although entanglement in superconducting circuits has been limited so far to two qubits, the extension of entanglement to three, eight and ten qubits has been achieved among spins, ions and photons, respectively. A key question for solid-state quantum information processing is whether an engineered system could display the multi-qubit entanglement necessary for quantum error correction, which starts with tripartite entanglement. Here, using a circuit quantum electrodynamics architecture, we demonstrate deterministic production of three-qubit Greenberger-Horne-Zeilinger (GHZ) states with fidelity of 88 per cent, measured with quantum state tomography. Several entanglement witnesses detect genuine three-qubit entanglement by violating biseparable bounds by 830 ± 80 per cent. We demonstrate the first step of basic quantum error correction, namely the encoding of a logical qubit into a manifold of GHZ-like states using a repetition code. The integration of this encoding with decoding and error-correcting steps in a feedback loop will be the next step for quantum computing with integrated circuits.
Circuit-extension handshakes for Tor achieving forward secrecy in a quantum world
Directory of Open Access Journals (Sweden)
Schanck John M.
2016-10-01
Full Text Available We propose a circuit extension handshake for Tor that is forward secure against adversaries who gain quantum computing capabilities after session negotiation. In doing so, we refine the notion of an authenticated and confidential channel establishment (ACCE protocol and define pre-quantum, transitional, and post-quantum ACCE security. These new definitions reflect the types of adversaries that a protocol might be designed to resist. We prove that, with some small modifications, the currently deployed Tor circuit extension handshake, ntor, provides pre-quantum ACCE security. We then prove that our new protocol, when instantiated with a post-quantum key encapsulation mechanism, achieves the stronger notion of transitional ACCE security. Finally, we instantiate our protocol with NTRU-Encrypt and provide a performance comparison between ntor, our proposal, and the recent design of Ghosh and Kate.
Error sensitivity to environmental noise in quantum circuits for chemical state preparation
Sawaya, Nicolas P D; McClean, Jarrod R; Aspuru-Guzik, Alán
2016-01-01
Calculating molecular energies is likely to be one of the first useful applications to achieve quantum supremacy, performing faster on a quantum than a classical computer. However, if future quantum devices are to produce accurate calculations, errors due to environmental noise and algorithmic approximations need to be characterized and reduced. In this study, we use the high performance qHiPSTER software to investigate the effects of environmental noise on the preparation of quantum chemistry states. We simulate nineteen 16-qubit quantum circuits under environmental noise, each corresponding to a unitary coupled cluster state preparation of a different molecule or molecular configuration. Additionally, we analyze the nature of simple gate errors in noise-free circuits of up to 40 qubits. We find that the Jordan-Wigner (JW) encoding produces consistently smaller errors under a noisy environment as compared to the Bravyi-Kitaev (BK) encoding. For the JW encoding, pure-dephasing noise is shown to produce substa...
Generation of a macroscopic entangled coherent state using quantum memories in circuit QED
Liu, Tong; Su, Qi-Ping; Xiong, Shao-Jie; Liu, Jin-Ming; Yang, Chui-Ping; Nori, Franco
2016-01-01
W-type entangled states can be used as quantum channels for, e.g., quantum teleportation, quantum dense coding, and quantum key distribution. In this work, we propose a way to generate a macroscopic W-type entangled coherent state using quantum memories in circuit QED. The memories considered here are nitrogen-vacancy center ensembles (NVEs), each located in a different cavity. This proposal does not require initially preparing each NVE in a coherent state instead of a ground state, which should significantly reduce its experimental difficulty. For most of the operation time, each cavity remains in a vacuum state, thus decoherence caused by the cavity decay and the unwanted inter-cavity crosstalk are greatly suppressed. Moreover, only one external-cavity coupler qubit is needed, which simplifies the circuit. PMID:27562055
Quantum interference in heterogeneous superconducting-photonic circuits on a silicon chip
Schuck, Carsten; Fan, Linran; Ma, Xiao-Song; Poot, Menno; Tang, Hong X
2015-01-01
Quantum information processing holds great promise for communicating and computing data efficiently. However, scaling current photonic implementation approaches to larger system size remains an outstanding challenge for realizing disruptive quantum technology. Two main ingredients of quantum information processors are quantum interference and single-photon detectors. Here we develop a hybrid superconducting-photonic circuit system to show how these elements can be combined in a scalable fashion on a silicon chip. We demonstrate the suitability of this approach for integrated quantum optics by interfering and detecting photon pairs directly on the chip with waveguide-coupled single-photon detectors. Using a directional coupler implemented with silicon nitride nanophotonic waveguides, we observe 97% interference visibility when measuring photon statistics with two monolithically integrated superconducting single photon detectors. The photonic circuit and detector fabrication processes are compatible with standa...
Universal holonomic quantum gates in decoherence-free subspace on superconducting circuits
Xue, Zheng-Yuan; Zhou, Jian; Wang, Z. D.
2015-08-01
To implement a set of universal quantum logic gates based on non-Abelian geometric phases, it is conventional wisdom that quantum systems beyond two levels are required, which is extremely difficult to fulfill for superconducting qubits and appears to be a main reason why only single-qubit gates were implemented in a recent experiment [A. A. Abdumalikov, Jr. et al., Nature (London) 496, 482 (2013), 10.1038/nature12010]. Here we propose to realize nonadiabatic holonomic quantum computation in decoherence-free subspace on circuit QED, where one can use only the two levels in transmon qubits, a usual interaction, and a minimal resource for the decoherence-free subspace encoding. In particular, our scheme not only overcomes the difficulties encountered in previous studies but also can still achieve considerably large effective coupling strength, such that high-fidelity quantum gates can be achieved. Therefore, the present scheme makes realizing robust holonomic quantum computation with superconducting circuits very promising.
A nanoCryotron comparator can connect single-flux quantum circuits to conventional electronics
Zhao, Qing-Yuan; Dane, Andrew E; Berggren, Karl K; Ortlepp, Thomas
2016-01-01
Integration with conventional electronics offers a straightforward and economical approach to upgrading existing superconducting technologies, such as scaling up superconducting detectors into large arrays and combining single flux quantum (SFQ) digital circuits with semiconductor logic and memories. However, direct output signals from superconducting devices (e.g., Josephson junctions) are usually not compatible with the input requirements of conventional devices (e.g., transistors). Here, we demonstrate the use of a single three-terminal superconducting-nanowire device, called the nanocryotron (nTron), as a digital comparator to combine SFQ circuits with mature semiconductor circuits such as complementary metal oxide semiconductor (CMOS) circuits. Since SFQ circuits can digitize output signals from general superconducting devices and CMOS circuits can interface existing CMOS-compatible electronics, our results demonstrate the feasibility of a general architecture that uses an nTron as an interface to realiz...
Experimental Monte Carlo Quantum Process Certification
Steffen, L; Fedorov, A; Baur, M; Wallraff, A
2012-01-01
Experimental implementations of quantum information processing have now reached a level of sophistication where quantum process tomography is impractical. The number of experimental settings as well as the computational cost of the data post-processing now translates to days of effort to characterize even experiments with as few as 8 qubits. Recently a more practical approach to determine the fidelity of an experimental quantum process has been proposed, where the experimental data is compared directly to an ideal process using Monte Carlo sampling. Here we present an experimental implementation of this scheme in a circuit quantum electrodynamics setup to determine the fidelity of two qubit gates, such as the cphase and the cnot gate, and three qubit gates, such as the Toffoli gate and two sequential cphase gates.
Directory of Open Access Journals (Sweden)
Hong-Quan ZHao
2012-01-01
Full Text Available One-dimensional nanowire quantum devices and basic quantum logic AND and OR unit on hexagonal nanowire units controlled by wrap gate (WPG were designed and fabricated on GaAs-based one-dimensional electron gas (1-DEG regular nanowire network with hexagonal topology. These basic quantum logic units worked correctly at 35 K, and clear quantum conductance was achieved on the node device, logic AND circuit unit, and logic OR circuit unit. Binary-decision-diagram- (BDD- based arithmetic logic unit (ALU is realized on GaAs-based regular nanowire network with hexagonal topology by the same fabrication method as that of the quantum devices and basic circuits. This BDD-based ALU circuit worked correctly at room temperature. Since these quantum devices and circuits are basic units of the BDD ALU combinational circuit, the possibility of integrating these quantum devices and basic quantum circuits into the BDD-based quantum circuit with more complicated structures was discussed. We are prospecting the realization of quantum BDD combinational circuitries with very small of energy consumption and very high density of integration.
Ding, Yunhong; Bacco, Davide; Dalgaard, Kjeld; Cai, Xinlun; Zhou, Xiaoqi; Rottwitt, Karsten; Oxenløwe, Leif Katsuo
2017-06-01
Quantum key distribution provides an efficient means to exchange information in an unconditionally secure way. Historically, quantum key distribution protocols have been based on binary signal formats, such as two polarization states, and the transmitted information efficiency of the quantum key is intrinsically limited to 1 bit/photon. Here we propose and experimentally demonstrate, for the first time, a high-dimensional quantum key distribution protocol based on space division multiplexing in multicore fiber using silicon photonic integrated lightwave circuits. We successfully realized three mutually unbiased bases in a four-dimensional Hilbert space, and achieved low and stable quantum bit error rate well below both the coherent attack and individual attack limits. Compared to previous demonstrations, the use of a multicore fiber in our protocol provides a much more efficient way to create high-dimensional quantum states, and enables breaking the information efficiency limit of traditional quantum key distribution protocols. In addition, the silicon photonic circuits used in our work integrate variable optical attenuators, highly efficient multicore fiber couplers, and Mach-Zehnder interferometers, enabling manipulating high-dimensional quantum states in a compact and stable manner. Our demonstration paves the way to utilize state-of-the-art multicore fibers for noise tolerance high-dimensional quantum key distribution, and boost silicon photonics for high information efficiency quantum communications.
Critical assessment of two-qubit post-Markovian master equations
Campbell, S; Mazzola, L; Gullo, N Lo; Vacchini, B; Busch, Th; Paternostro, M
2012-01-01
A post-Markovian master equation has been recently proposed as a tool to describe the evolution of a system coupled to a memory-keeping environment [A. Shabani and D. A. Lidar, Phys. Rev. A 71, 020101 (R) (2005)]. For a single qubit affected by appropriately chosen environmental conditions, the corresponding dynamics is always legitimate and physical. Here we extend such situation to the case of two qubits, only one of which experiences the environmental effects. We show how, despite the innocence of such an extension, the introduction of the second qubit should be done cum grano salis to avoid consequences such as the breaking of the positivity of the associated dynamical map. This hints at the necessity of using care when adopting phenomenologically derived models for evolutions occurring outside the Markovian framework.
Entanglement dynamics of a two-qubit system coupled individually to Ohmic baths
Duan, Liwei; Chen, Qinghu; Zhao, Yang
2013-01-01
The Davydov D1 ansatz, which assigns an individual bosonic trajectory to each spin state, is an efficient, yet accurate trial state for time-dependent variation of the the spin-boson model [J. Chem. Phys. 138, 084111 (2013)]. In this work, the Dirac-Frenkel time-dependent variational procedure utilizing the Davydov D1 ansatz is implemented to study entanglement dynamics of two qubits under the influence of two independent baths. The Ohmic spectral density is used without the Born-Markov approximation or the rotating-wave approximation. In the strong coupling regime the entanglement sudden death is always found to exist, while at the intermediate coupling regime, the entanglement dynamics calculated by Davydov D1 ansatz displays oscillatory behavior in addition to entanglement sudden death and revival.
Sudden Death, Birth and Stable Entanglement in a Two-Qubit Heisenberg XY Spin Chain
Institute of Scientific and Technical Information of China (English)
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.
Complete multiple round quantum dense coding with quantum logical network
Institute of Scientific and Technical Information of China (English)
LI ChunYan; LI XiHan; DENG FuGuo; ZHOU Ping; ZHOU HongYu
2007-01-01
We present a complete multiple round quantum dense coding scheme for improving the source capacity of that introduced recently by Zhang et al. The receiver resorts to two qubits for storing the four local unitary operations in each round.
Geometric reduction of dynamical nonlocality in nanoscale quantum circuits
Strambini, E.; Makarenko, K. S.; Abulizi, G.; de Jong, M. P.; van der Wiel, W. G.
2016-01-01
Nonlocality is a key feature discriminating quantum and classical physics. Quantum-interference phenomena, such as Young’s double slit experiment, are one of the clearest manifestations of nonlocality, recently addressed as dynamical to specify its origin in the quantum equations of motion. It is well known that loss of dynamical nonlocality can occur due to (partial) collapse of the wavefunction due to a measurement, such as which-path detection. However, alternative mechanisms affecting dynamical nonlocality have hardly been considered, although of crucial importance in many schemes for quantum information processing. Here, we present a fundamentally different pathway of losing dynamical nonlocality, demonstrating that the detailed geometry of the detection scheme is crucial to preserve nonlocality. By means of a solid-state quantum-interference experiment we quantify this effect in a diffusive system. We show that interference is not only affected by decoherence, but also by a loss of dynamical nonlocality based on a local reduction of the number of quantum conduction channels of the interferometer. With our measurements and theoretical model we demonstrate that this mechanism is an intrinsic property of quantum dynamics. Understanding the geometrical constraints protecting nonlocality is crucial when designing quantum networks for quantum information processing.
Geometric reduction of dynamical nonlocality in nanoscale quantum circuits
Strambini, E.; Makarenko, K. S.; Abulizi, G.; de Jong, M. P.; van der Wiel, W. G.
2016-01-01
Nonlocality is a key feature discriminating quantum and classical physics. Quantum-interference phenomena, such as Young’s double slit experiment, are one of the clearest manifestations of nonlocality, recently addressed as dynamical to specify its origin in the quantum equations of motion. It is well known that loss of dynamical nonlocality can occur due to (partial) collapse of the wavefunction due to a measurement, such as which-path detection. However, alternative mechanisms affecting dynamical nonlocality have hardly been considered, although of crucial importance in many schemes for quantum information processing. Here, we present a fundamentally different pathway of losing dynamical nonlocality, demonstrating that the detailed geometry of the detection scheme is crucial to preserve nonlocality. By means of a solid-state quantum-interference experiment we quantify this effect in a diffusive system. We show that interference is not only affected by decoherence, but also by a loss of dynamical nonlocality based on a local reduction of the number of quantum conduction channels of the interferometer. With our measurements and theoretical model we demonstrate that this mechanism is an intrinsic property of quantum dynamics. Understanding the geometrical constraints protecting nonlocality is crucial when designing quantum networks for quantum information processing. PMID:26732751
Nori, Franco
2012-02-01
This talk will present an overview of some of our recent results on atomic physics and quantum optics using superconducting circuits. Particular emphasis will be given to photons interacting with qubits, interferometry, the Dynamical Casimir effect, and also studying Majorana fermions using superconducting circuits.[4pt] References available online at our web site:[0pt] J.Q. You, Z.D. Wang, W. Zhang, F. Nori, Manipulating and probing Majorana fermions using superconducting circuits, (2011). Arxiv. J.R. Johansson, G. Johansson, C.M. Wilson, F. Nori, Dynamical Casimir effect in a superconducting coplanar waveguide, Phys. Rev. Lett. 103, 147003 (2009). [0pt] J.R. Johansson, G. Johansson, C.M. Wilson, F. Nori, Dynamical Casimir effect in superconducting microwave circuits, Phys. Rev. A 82, 052509 (2010). [0pt] C.M. Wilson, G. Johansson, A. Pourkabirian, J.R. Johansson, T. Duty, F. Nori, P. Delsing, Observation of the Dynamical Casimir Effect in a superconducting circuit. Nature, in press (Nov. 2011). P.D. Nation, J.R. Johansson, M.P. Blencowe, F. Nori, Stimulating uncertainty: Amplifying the quantum vacuum with superconducting circuits, Rev. Mod. Phys., in press (2011). [0pt] J.Q. You, F. Nori, Atomic physics and quantum optics using superconducting circuits, Nature 474, 589 (2011). [0pt] S.N. Shevchenko, S. Ashhab, F. Nori, Landau-Zener-Stuckelberg interferometry, Phys. Reports 492, 1 (2010). [0pt] I. Buluta, S. Ashhab, F. Nori. Natural and artificial atoms for quantum computation, Reports on Progress in Physics 74, 104401 (2011). [0pt] I.Buluta, F. Nori, Quantum Simulators, Science 326, 108 (2009). [0pt] L.F. Wei, K. Maruyama, X.B. Wang, J.Q. You, F. Nori, Testing quantum contextuality with macroscopic superconducting circuits, Phys. Rev. B 81, 174513 (2010). [0pt] J.Q. You, X.-F. Shi, X. Hu, F. Nori, Quantum emulation of a spin system with topologically protected ground states using superconducting quantum circuit, Phys. Rev. A 81, 063823 (2010).
Olaya-Castro, Alexandra; Johnson, Neil F.; Quiroga, Luis
2004-08-01
We present an efficient scheme for the controlled generation of pure two-qubit states possessing any desired degree of entanglement and a prescribed symmetry. This is achieved in two-qubit-cavity QED systems (e.g., cold-trapped ions and flying atoms) via on-resonance ion- or atom-cavity couplings, which are time dependent and asymmetric, yielding a trapping vacuum state condition which does not arise for identical couplings. A duality in the role of the coupling ratio yields states with a given concurrence but opposing symmetries. Both the trapping state condition and the resulting entanglement power are robust against decoherence channels.
Dissipative preparation of entanglement in quantum optical and solid state systems
DEFF Research Database (Denmark)
Reiter, Florentin
Quantum mechanics is an immensely successful theory which is essential for the explanation of numerous phenomena in atomic physics, solid state physics, nuclear physics and elementary particle physics. Quantum theory also involves effects which have no analogy in the classical world. In particular...... superconducting qubits in a circuit QED setup. Combining resonator photon loss, a dissipative process already present in the setup, with an effective two-photon microwave drive, we engineer an effective decay mechanism which prepares a maximally entangled state of two qubits. We find that high fidelities......, quantum entanglement is a correlation predicted by quantum mechanics, but not by classical physics. As an observable property it is indispensable for our understanding of nature. In addition, entangled states are important in quantum computation, quantum communication and quantum measurement protocols...
Hybrid quantum circuit with a superconducting qubit coupled to an electron spin ensemble
Energy Technology Data Exchange (ETDEWEB)
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.
Dominance of quantum over classical correlations: entropic and geometric approach
Walczak, Zbigniew; Wintrowicz, Iwona; Zakrzewska, Katarzyna
2013-01-01
Recently, it has been shown that there exist quantum states for which quantum correlations dominate over classical correlations. Inspired by this observation, we investigate the problem of quantum correlations dominance for two-qubit Bell diagonal states in the Ollivier--Zurek paradigm, using both entropic and geometric approach to quantification of classical and quantum correlations. In particular, we estimate numerically the amount of two-qubit Bell diagonal states for which quantum correla...
Tamaki, Kiyoshi
2010-01-01
One of the simplest security proofs of quantum key distribution is based on the so-called complementarity scenario, which involves the complementarity control of an actual protocol and a virtual protocol [M. Koashi, e-print arXiv:0704.3661 (2007)]. The existing virtual protocol has a limitation in classical postprocessing, i.e., the syndrome for the error-correction step has to be encrypted. In this paper, we remove this limitation by constructing a quantum circuit for the virtual protocol. Moreover, our circuit with a shield system gives an intuitive proof of why adding noise to the sifted key increases the bit error rate threshold in the general case in which one of the parties does not possess a qubit. Thus, our circuit bridges the simple proof and the use of wider classes of classical postprocessing.
Optimal Control of 1D and 2D Circuit QED
Fisher, R; Glaser, S J; Marquardt, F; Schulte-Herbrueggen, T
2009-01-01
Optimal control can be used to significantly improve multi-qubit gates in quantum information processing hardware architectures based on superconducting circuit quantum electrodynamics. We apply this approach not only to dispersive gates of two qubits inside a cavity, but, more generally, to architectures based on two-dimensional arrays of cavities and qubits. For high-fidelity gate operations, simultaneous evolutions of controls and couplings in the two coupling dimensions of cavity grids are shown to be significantly faster than conventional sequential implementations. Even under experimentally realistic conditions speedups by a factor of three can be gained. The methods immediately scale to large grids and indirect gates between arbitrary pairs of qubits on the grid. They are anticipated to be paradigmatic for 2D arrays and lattices of controllable qubits.
Designing reversible arithmetic, logic circuit to implement micro-operation in quantum computation
Kalita, Gunajit; Saikia, Navajit
2016-10-01
The futuristic computing is desired to be more power full with low-power consumption. That is why quantum computing has been a key area of research for quite some time and is getting more and more attention. Quantum logic being reversible, a significant amount of contributions has been reported on reversible logic in recent times. Reversible circuits are essential parts of quantum computers, and hence their designs are of great importance. In this paper, designs of reversible circuits are proposed using a recently proposed reversible gate for arithmetic and logic operations to implement various micro-operations (simple add and subtract, add with carry, subtract with borrow, transfer, incrementing, decrementing etc., and logic operations like XOR, XNOR, complementing etc.) in a reversible computer like quantum computer. The two new reversible designs proposed here for half adder and full adders are also used in the presented reversible circuits to implement various microoperations. The quantum costs of these designs are comparable. Many of the implemented micro-operations are not seen in previous literatures. The performances of the proposed circuits are compared with existing designs wherever available.
Josephson directional amplifier for quantum measurement of superconducting circuits.
Abdo, Baleegh; Sliwa, Katrina; Shankar, S; Hatridge, Michael; Frunzio, Luigi; Schoelkopf, Robert; Devoret, Michel
2014-04-25
We realize a microwave quantum-limited amplifier that is directional and can therefore function without the front circulator needed in many quantum measurements. The amplification takes place in only one direction between the input and output ports. Directionality is achieved by multipump parametric amplification combined with wave interference. We have verified the device noise performances by using it to read out a superconducting qubit and observed quantum jumps. With an improved version of this device, the qubit and preamplifer could be integrated on the same chip.
Institute of Scientific and Technical Information of China (English)
Li Wen-Dong; Zhang Jian-Li; Gu Yong-Jian
2006-01-01
Deterministic and exact teleportation can be achieved via two partially entangled pairs of particles[Gu Y J 2006 Opt.Comm.259 385].The key point of the protocol is a generalized measurement described by a positive operator valued measure, which can be realized by performing a unitary operation in the extended space and a conventional Von Neumann orthogonal measurement.By decomposing the evolution process from the initial state to the final state, we construct the quantum circuits for realizing the unitary operation with quantum Toffoli gates, and thus provide a physical means to realize the teleportation.Our method for constructing quantum circuits differs from the usual methods based on decomposition of unitary matrices, and is convenient for a large class of quantum processes involving generalized measurements.
Probabilistic Teleportation of an Arbitrary Two-Particle State and Its Quantum Circuits
Institute of Scientific and Technical Information of China (English)
GUO Zhan-Ying; FANG Jian-Xing; ZHU Shi-Qun; QIAN Xue-Min
2006-01-01
Two simple schemes for probabilistic teleportation of an arbitrary unknown two-particle state using a non-maximally entangled EPR pair and a non-maximally entangled GHZ state as quantum channels are proposed.After receiving Alice's Bell state measurement results, Bob performs a collective unitary transformation on his inherent particles without introducing the auxiliary qubit. The original state can be probabilistically teleported. Meanwhile,quantum circuits for realization of successful teleportation are also presented.
NV-based quantum memories coupled to photonic integrated circuits
Mouradian, Sara; Schröder, Tim; Zheng, Jiabao; Lu, Tsung-Ju; Choi, Hyeongrak; Wan, Noel; Walsh, Michael; Bersin, Eric; Englund, Dirk
2016-09-01
The negatively charged nitrogen vacancy (NV) center in diamond is a promising solid-state quantum memory. However, developing networks comprising such quantum memories is limited by the fabrication yield of the quantum nodes and the collection efficiency of indistinguishable photons. In this letter, we report on advances on a hybrid quantum system that allows for scalable production of networks, even with low-yield node fabrication. Moreover, an NV center in a simple single mode diamond waveguide is shown in simulation and experiment to couple well to a single mode SiN waveguide with a simple adiabatic taper for optimal mode transfer. In addition, cavity enhancement of the zero phonon line of the NV center with a resonance coupled to the waveguide mode allows a simulated <1800 fold increase in the collection of photon states coherent with the state of the NV center into a single frequency and spatial mode.
Observation of Majorization Principle for quantum algorithms via 3-D integrated photonic circuits
Flamini, Fulvio; Giordani, Taira; Bentivegna, Marco; Spagnolo, Nicoló; Crespi, Andrea; Corrielli, Giacomo; Osellame, Roberto; Martin-Delgado, Miguel Angel; Sciarrino, Fabio
2016-01-01
The Majorization Principle is a fundamental statement governing the dynamics of information processing in optimal and efficient quantum algorithms. While quantum computation can be modeled to be reversible, due to the unitary evolution undergone by the system, these quantum algorithms are conjectured to obey a quantum arrow of time dictated by the Majorization Principle: the probability distribution associated to the outcomes gets ordered step-by-step until achieving the result of the computation. Here we report on the experimental observation of the effects of the Majorization Principle for two quantum algorithms, namely the quantum fast Fourier transform and a recently introduced validation protocol for the certification of genuine many-boson interference. The demonstration has been performed by employing integrated 3-D photonic circuits fabricated via femtosecond laser writing technique, which allows to monitor unambiguously the effects of majorization along the execution of the algorithms. The measured ob...
Random Quantum Circuits and Pseudo-Random Operators: Theory and Applications
Emerson, J
2003-01-01
Pseudo-random operators consist of sets of operators that exhibit many of the important statistical features of uniformly distributed random operators. Such pseudo-random sets of operators are most useful whey they may be parameterized and generated on a quantum processor in a way that requires exponentially fewer resources than direct implementation of the uniformly random set. Efficient pseudo-random operators can overcome the exponential cost of random operators required for quantum communication tasks such as super-dense coding of quantum states and approximately secure quantum data-hiding, and enable efficient stochastic methods for noise estimation on prototype quantum processors. This paper summarizes some recently published work demonstrating a random circuit method for the implementation of pseudo-random unitary operators on a quantum processor [Emerson et al., Science 302:2098 (Dec.~19, 2003)], and further elaborates the theory and applications of pseudo-random states and operators.
On-chip single photon filtering and multiplexing in hybrid quantum photonic circuits.
Elshaari, Ali W; Zadeh, Iman Esmaeil; Fognini, Andreas; Reimer, Michael E; Dalacu, Dan; Poole, Philip J; Zwiller, Val; Jöns, Klaus D
2017-08-30
Quantum light plays a pivotal role in modern science and future photonic applications. Since the advent of integrated quantum nanophotonics different material platforms based on III-V nanostructures-, colour centers-, and nonlinear waveguides as on-chip light sources have been investigated. Each platform has unique advantages and limitations; however, all implementations face major challenges with filtering of individual quantum states, scalable integration, deterministic multiplexing of selected quantum emitters, and on-chip excitation suppression. Here we overcome all of these challenges with a hybrid and scalable approach, where single III-V quantum emitters are positioned and deterministically integrated in a complementary metal-oxide-semiconductor-compatible photonic circuit. We demonstrate reconfigurable on-chip single-photon filtering and wavelength division multiplexing with a foot print one million times smaller than similar table-top approaches, while offering excitation suppression of more than 95 dB and efficient routing of single photons over a bandwidth of 40 nm. Our work marks an important step to harvest quantum optical technologies' full potential.Combining different integration platforms on the same chip is currently one of the main challenges for quantum technologies. Here, Elshaari et al. show III-V Quantum Dots embedded in nanowires operating in a CMOS compatible circuit, with controlled on-chip filtering and tunable routing.
Institute of Scientific and Technical Information of China (English)
QIAN Li; FANG Jian-Xing
2009-01-01
We study the effects of Dzyaloshinski-Moriya(DM)interaction on entanglement and teleportation in a two-qubit Ising system with intrinsic decoherence taken into account.It is found that for the unentangled state,DM interaction is a benefit for entanglement and teleportation.
Concurrent remote entanglement with quantum error correction against photon losses
Roy, Ananda; Stone, A. Douglas; Jiang, Liang
2016-09-01
Remote entanglement of distant, noninteracting quantum entities is a key primitive for quantum information processing. We present a protocol to remotely entangle two stationary qubits by first entangling them with propagating ancilla qubits and then performing a joint two-qubit measurement on the ancillas. Subsequently, single-qubit measurements are performed on each of the ancillas. We describe two continuous variable implementations of the protocol using propagating microwave modes. The first implementation uses propagating Schr o ̈ dinger cat states as the flying ancilla qubits, a joint-photon-number-modulo-2 measurement of the propagating modes for the two-qubit measurement, and homodyne detections as the final single-qubit measurements. The presence of inefficiencies in realistic quantum systems limit the success rate of generating high fidelity Bell states. This motivates us to propose a second continuous variable implementation, where we use quantum error correction to suppress the decoherence due to photon loss to first order. To that end, we encode the ancilla qubits in superpositions of Schrödinger cat states of a given photon-number parity, use a joint-photon-number-modulo-4 measurement as the two-qubit measurement, and homodyne detections as the final single-qubit measurements. We demonstrate the resilience of our quantum-error-correcting remote entanglement scheme to imperfections. Further, we describe a modification of our error-correcting scheme by incorporating additional individual photon-number-modulo-2 measurements of the ancilla modes to improve the success rate of generating high-fidelity Bell states. Our protocols can be straightforwardly implemented in state-of-the-art superconducting circuit-QED systems.
Generation of Fock states in a superconducting quantum circuit.
Hofheinz, Max; Weig, E M; Ansmann, M; Bialczak, Radoslaw C; Lucero, Erik; Neeley, M; O'Connell, A D; Wang, H; Martinis, John M; Cleland, A N
2008-07-17
Spin systems and harmonic oscillators comprise two archetypes in quantum mechanics. The spin-1/2 system, with two quantum energy levels, is essentially the most nonlinear system found in nature, whereas the harmonic oscillator represents the most linear, with an infinite number of evenly spaced quantum levels. A significant difference between these systems is that a two-level spin can be prepared in an arbitrary quantum state using classical excitations, whereas classical excitations applied to an oscillator generate a coherent state, nearly indistinguishable from a classical state. Quantum behaviour in an oscillator is most obvious in Fock states, which are states with specific numbers of energy quanta, but such states are hard to create. Here we demonstrate the controlled generation of multi-photon Fock states in a solid-state system. We use a superconducting phase qubit, which is a close approximation to a two-level spin system, coupled to a microwave resonator, which acts as a harmonic oscillator, to prepare and analyse pure Fock states with up to six photons. We contrast the Fock states with coherent states generated using classical pulses applied directly to the resonator.
Tunable quantum interference in a 3D integrated circuit.
Chaboyer, Zachary; Meany, Thomas; Helt, L G; Withford, Michael J; Steel, M J
2015-04-27
Integrated photonics promises solutions to questions of stability, complexity, and size in quantum optics. Advances in tunable and non-planar integrated platforms, such as laser-inscribed photonics, continue to bring the realisation of quantum advantages in computation and metrology ever closer, perhaps most easily seen in multi-path interferometry. Here we demonstrate control of two-photon interference in a chip-scale 3D multi-path interferometer, showing a reduced periodicity and enhanced visibility compared to single photon measurements. Observed non-classical visibilities are widely tunable, and explained well by theoretical predictions based on classical measurements. With these predictions we extract Fisher information approaching a theoretical maximum. Our results open a path to quantum enhanced phase measurements.
Joo, Jaewoo; Ginossar, Eran
2016-06-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits.
Joo, Jaewoo; Ginossar, Eran
2016-06-01
We propose a deterministic scheme for teleporting an unknown qubit state through continuous-variable entangled states in superconducting circuits. The qubit is a superconducting two-level system and the bipartite quantum channel is a microwave photonic entangled coherent state between two cavities. A Bell-type measurement performed on the hybrid state of solid and photonic states transfers a discrete-variable unknown electronic state to a continuous-variable photonic cat state in a cavity mode. In order to facilitate the implementation of such complex protocols we propose a design for reducing the self-Kerr nonlinearity in the cavity. The teleporation scheme enables quantum information processing operations with circuit-QED based on entangled coherent states. These include state verification and single-qubit operations with entangled coherent states. These are shown to be experimentally feasible with the state of the art superconducting circuits.
A nanocryotron comparator can connect single-flux-quantum circuits to conventional electronics
Zhao, Qing-Yuan; McCaughan, Adam N.; Dane, Andrew E.; Berggren, Karl K.; Ortlepp, Thomas
2017-04-01
Integration with conventional electronics offers a straightforward and economical approach to upgrading existing superconducting technologies, such as scaling up superconducting detectors into large arrays and combining single flux quantum (SFQ) digital circuits with semiconductor logic gates and memories. However, direct output signals from superconducting devices (e.g., Josephson junctions) are usually not compatible with the input requirements of conventional devices (e.g., transistors). Here, we demonstrate the use of a single three-terminal superconducting-nanowire device, called the nanocryotron (nTron), as a digital comparator to combine SFQ circuits with mature semiconductor circuits such as complementary metal oxide semiconductor (CMOS) circuits. Since SFQ circuits can digitize output signals from general superconducting devices and CMOS circuits can interface existing CMOS-compatible electronics, our results demonstrate the feasibility of a general architecture that uses an nTron as an interface to realize a ‘super-hybrid’ system consisting of superconducting detectors, superconducting quantum electronics, CMOS logic gates and memories, and other conventional electronics.
Numerical characteristics of quantum computer simulation
Chernyavskiy, A.; Khamitov, K.; Teplov, A.; Voevodin, V.; Voevodin, Vl.
2016-12-01
The simulation of quantum circuits is significantly important for the implementation of quantum information technologies. The main difficulty of such modeling is the exponential growth of dimensionality, thus the usage of modern high-performance parallel computations is relevant. As it is well known, arbitrary quantum computation in circuit model can be done by only single- and two-qubit gates, and we analyze the computational structure and properties of the simulation of such gates. We investigate the fact that the unique properties of quantum nature lead to the computational properties of the considered algorithms: the quantum parallelism make the simulation of quantum gates highly parallel, and on the other hand, quantum entanglement leads to the problem of computational locality during simulation. We use the methodology of the AlgoWiki project (algowiki-project.org) to analyze the algorithm. This methodology consists of theoretical (sequential and parallel complexity, macro structure, and visual informational graph) and experimental (locality and memory access, scalability and more specific dynamic characteristics) parts. Experimental part was made by using the petascale Lomonosov supercomputer (Moscow State University, Russia). We show that the simulation of quantum gates is a good base for the research and testing of the development methods for data intense parallel software, and considered methodology of the analysis can be successfully used for the improvement of the algorithms in quantum information science.
Davanco, Marcelo; Sapienza, Luca; Zhang, Chen-Zhao; Cardoso, Jose Vinicius De Miranda; Verma, Varun; Mirin, Richard; Nam, Sae Woo; Liu, Liu; Srinivasan, Kartik
2016-01-01
Photonic integration is an enabling technology for photonic quantum science, offering greater scalability, stability, and functionality than traditional bulk optics. Here, we describe a scalable, heterogeneous III-V/silicon integration platform to produce Si$_3$N$_4$ photonic circuits incorporating GaAs-based nanophotonic devices containing self-assembled InAs/GaAs quantum dots. We demonstrate pure singlephoton emission from individual quantum dots in GaAs waveguides and cavities - where strong control of spontaneous emission rate is observed - directly launched into Si$_3$N$_4$ waveguides with > 90 % efficiency through evanescent coupling. To date, InAs/GaAs quantum dots constitute the most promising solidstate triggered single-photon sources, offering bright, pure and indistinguishable emission that can be electrically and optically controlled. Si$_3$N$_4$ waveguides offer low-loss propagation, tailorable dispersion and high Kerr nonlinearities, desirable for linear and nonlinear optical signal processing d...
Most robust and fragile two-qubit entangled states under depolarizing channels
Pang, Chao-Qian; Jiang, Yue; Liang, Mai-Lin
2012-01-01
In the two-qubit system under the local depolarizing channels, the most robust and the most fragile states for a given concurrence or negativity are derived. For the one-sided channel, with the aid of the evolution equation for entanglement given by Konrad \\emph{et al.} [Nat. Phys. 4, 99 (2008)], the pure states are proved to be the most robust. Based on a generalization of the evolution equation, we classify the ansatz states in our investigation by the amount of robustness, and consequently derive the most fragile states. For the two-sided channel, the pure states are proved to be the most robust for a fixed concurrence, but is the most fragile with a given negativity when the channel is uniform. Under the uniform channel, for a given negativity, the most robust states are the ones with the maximal concurrence, which are also the most fragile states when the concurrence is given in the region of [1/2,1]. When the entanglement approaches zero, the most fragile states for a given negativity become the pure st...
Full control of quadruple quantum dot circuit charge states in the single electron regime
Energy Technology Data Exchange (ETDEWEB)
Delbecq, M. R., E-mail: matthieu.delbecq@riken.jp; Nakajima, T.; Otsuka, T.; Amaha, S. [RIKEN, Center for Emergent Matter Science, 3-1 Wako-shi, Saitama 351-0198 (Japan); Watson, J. D. [Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States); Manfra, M. J. [Department of Physics, Purdue University, West Lafayette, Indiana 47907 (United States); Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907 (United States); School of Materials Engineering, Purdue University, West Lafayette, Indiana 47907 (United States); School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 47907 (United States); Tarucha, S. [RIKEN, Center for Emergent Matter Science, 3-1 Wako-shi, Saitama 351-0198 (Japan); Department of Applied Physics, University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-8656 (Japan)
2014-05-05
We report the realization of an array of four tunnel coupled quantum dots in the single electron regime, which is the first required step toward a scalable solid state spin qubit architecture. We achieve an efficient tunability of the system but also find out that the conditions to realize spin blockade readout are not as straightforwardly obtained as for double and triple quantum dot circuits. We use a simple capacitive model of the series quadruple quantum dots circuit to investigate its complex charge state diagrams and are able to find the most suitable configurations for future Pauli spin blockade measurements. We then experimentally realize the corresponding charge states with a good agreement to our model.
Circuit models and SPICE macro-models for quantum Hall effect devices
Ortolano, Massimo
2015-01-01
Quantum Hall effect (QHE) devices are a pillar of modern quantum electrical metrology. Electrical networks including one or more QHE elements can be used as quantum resistance and impedance standards. The analysis of these networks allows metrologists to evaluate the effect of the inevitable parasitic parameters on their performance as standards. This paper presents a systematic analysis of the various circuit models for QHE elements proposed in the literature, and the development of a new model. This last model is particularly suited to be employed with the analogue electronic circuit simulator SPICE. The SPICE macro-model and examples of SPICE simulations, validated by comparison with the corresponding analytical solution and/or experimental data, are provided.
All-high-Tc superconductor rapid-single-flux-quantum circuit operating at ˜30 K
Shokhor, S.; Nadgorny, B.; Gurvitch, M.; Semenov, V.; Polyakov, Yu.; Likharev, K.; Hou, S. Y.; Phillips, Julia M.
1995-11-01
We have implemented a simple circuit of the rapid single-flux-quantum (RSFQ) logic family using a single-layer YBa2Cu3O7-x thin-film structure with 14 in-plane Josephson junctions formed by direct electron beam writing. The circuit includes two dc/SFQ converters, two Josephson transmission lines, a complete RS SFQ flip-flop, and an SFQ/dc converter (readout SQUID). Low-frequency testing has shown that the dc-current-biased circuit operates correctly and reliably at T˜30 K, a few degrees below the effective critical temperature of the junctions. Prospects for a further increase of the operation temperature and implementation of more complex RSFQ circuits are discussed in brief.
How to simulate a universal quantum computer using negative probabilities
Hofmann, Holger F.
2009-07-01
The concept of negative probabilities can be used to decompose the interaction of two qubits mediated by a quantum controlled-NOT into three operations that require only classical interactions (that is, local operations and classical communication) between the qubits. For a single gate, the probabilities of the three operations are 1, 1 and -1. This decomposition can be applied in a probabilistic simulation of quantum computation by randomly choosing one of the three operations for each gate and assigning a negative statistical weight to the outcomes of sequences with an odd number of negative probability operations. The maximal exponential speed-up of a quantum computer can then be evaluated in terms of the increase in the number of sequences needed to simulate a single operation of the quantum circuit.
High critical temperature superconductor Josephson junctions for quantum circuit applications
Energy Technology Data Exchange (ETDEWEB)
Bauch, T; Gustafsson, D; Cedergren, K; Nawaz, S; Mumtaz Virk, M; Lombardi, F [Department of Microtechnology and Nanoscience, MC2, Chalmers University of Technology, Goeteborg (Sweden); Pettersson, H; Olsson, E [Department of Applied Physics, Chalmers University of Technology, Goeteborg (Sweden)], E-mail: bauch@chalmers.se
2009-12-15
Recent findings of macroscopic quantum properties in high critical temperature superconductor (HTS) Josephson junctions (JJs) point toward the need to revise the role of zero energy quasi-particles in this novel superconductor. We will discuss the possibility of designing superconducting artificial atoms in a transmon configuration to study the low energy excitation spectra of HTS. We have engineered high quality grain boundary JJs on low dielectric constant substrates. By fabricating submicron junctions, we extract values of capacitance and Josephson critical current densities that satisfy the main transmon design requirements. Moreover, the measured critical current noise power extrapolated at 1 Hz gives a dephasing time of 25 ns, which indicates that the observation of macroscopic quantum coherent effects in HTS JJ is a feasible task.
Photonic integrated circuits based on quantum well intermixing techniques
Hou, Lianping; Marsh, John H.
2016-01-01
The passive sections of a monolithic device must have a wider bandgap than the active regions to reduce losses due to direct interband absorption. Such bandgap engineering is usually realized by complicated regrown butt-joint or selective-area growth techniques. We, however, have developed a simple, flexible and low-cost alternative technique – quantum well intermixing (QWI) – to increase the bandgap in selected areas of an integrated device post-growth. To verify the QWI process, we have fab...
Photonic Integrated Circuits Based on Quantum well Intermixing Techniques
Hou, Lianping; John H. Marsh
2016-01-01
The passive sections of a monolithic device must have a wider bandgap than the active regions to reduce losses due to direct interband absorption. Such bandgap engineering is usually realized by complicated regrown butt-joint or selective-area growth techniques. We, however, have developed a simple, flexible and low-cost alternative technique – quantum well intermixing (QWI) – to increase the bandgap in selected areas of an integrated device post-growth. To verify the QWI process, we have fab...
Quantum Information Transfer in Circuit QED with Landau-Zener Tunneling
Institute of Scientific and Technical Information of China (English)
LI Jun-Wang; WU Chun-Wang; DAI Hong-Yi
2011-01-01
We propose a scheme to implement quantum information transfer between Cooper-pair boxes (CPBs) in a circuit quantum electrodynamic (QED) system with Landau-Zener tunneling. The system consists of two CPB qubits and a one-dimensional transmission line resonator (TLR). By analytically solving the eigenequation and numerically calculating the transition probability, the results show the quantum state transfer from one qubit to another via a fast adiabatic passage. The coupling mechanism is robust against decoherence effects.%@@ We propose a scheme to implement quantum information transfer between Cooper-pair boxes(CPBs)in a circuit quantum electrodynamic(QED)system with Landau-Zener tunneling.The system consists of two CPB qubits and a one-dimensional transmission line resonator(TLR).By analytically solving the eigenequation and numeri-cally calculating the transition probability,the results show the quantum state transfer from one qubit to another via a fast adiabatic passage.The coupling mechanism is robust against decoherence effects.
Digital-analog quantum simulation of generalized Dicke models with superconducting circuits
Lamata, Lucas
2017-01-01
We propose a digital-analog quantum simulation of generalized Dicke models with superconducting circuits, including Fermi- Bose condensates, biased and pulsed Dicke models, for all regimes of light-matter coupling. We encode these classes of problems in a set of superconducting qubits coupled with a bosonic mode implemented by a transmission line resonator. Via digital-analog techniques, an efficient quantum simulation can be performed in state-of-the-art circuit quantum electrodynamics platforms, by suitable decomposition into analog qubit-bosonic blocks and collective single-qubit pulses through digital steps. Moreover, just a single global analog block would be needed during the whole protocol in most of the cases, superimposed with fast periodic pulses to rotate and detune the qubits. Therefore, a large number of digital steps may be attained with this approach, providing a reduced digital error. Additionally, the number of gates per digital step does not grow with the number of qubits, rendering the simulation efficient. This strategy paves the way for the scalable digital-analog quantum simulation of many-body dynamics involving bosonic modes and spin degrees of freedom with superconducting circuits. PMID:28256559
Digital-analog quantum simulation of generalized Dicke models with superconducting circuits
Lamata, Lucas
2017-03-01
We propose a digital-analog quantum simulation of generalized Dicke models with superconducting circuits, including Fermi- Bose condensates, biased and pulsed Dicke models, for all regimes of light-matter coupling. We encode these classes of problems in a set of superconducting qubits coupled with a bosonic mode implemented by a transmission line resonator. Via digital-analog techniques, an efficient quantum simulation can be performed in state-of-the-art circuit quantum electrodynamics platforms, by suitable decomposition into analog qubit-bosonic blocks and collective single-qubit pulses through digital steps. Moreover, just a single global analog block would be needed during the whole protocol in most of the cases, superimposed with fast periodic pulses to rotate and detune the qubits. Therefore, a large number of digital steps may be attained with this approach, providing a reduced digital error. Additionally, the number of gates per digital step does not grow with the number of qubits, rendering the simulation efficient. This strategy paves the way for the scalable digital-analog quantum simulation of many-body dynamics involving bosonic modes and spin degrees of freedom with superconducting circuits.
Inducing nonclassical lasing via periodic drivings in circuit quantum electrodynamics.
Navarrete-Benlloch, Carlos; García-Ripoll, Juan José; Porras, Diego
2014-11-01
We show how a pair of superconducting qubits coupled to a microwave cavity mode can be used to engineer a single-atom laser that emits light into a nonclassical state. Our scheme relies on the dressing of the qubit-field coupling by periodic modulations of the qubit energy. In the dressed basis, the radiative decay of the first qubit becomes an effective incoherent pumping mechanism that injects energy into the system, hence turning dissipation to our advantage. A second, auxiliary qubit is used to shape the decay within the cavity, in such a way that lasing occurs in a squeezed basis of the cavity mode. We characterize the system both by mean-field theory and exact calculations. Our work may find applications in the generation of squeezing and entanglement in circuit QED, as well as in the study of dissipative few- and many-body phase transitions.
Hu, Yao-Hua; Tao, Ya-Ping; Tan, Yong-Gang; Yang, Hai-Feng
2017-02-01
Considering X-states the density matrixes of which look like the letter X, we propose a weak measurement-based entanglement protection protocol of two-qubit X-states under local amplitude damping channels using weak measurement and reversal operation. It is shown that, with increase of the decoherence parameter, the entanglement attenuates rapidly owing to the amplitude damping noise and even experiences entanglement sudden death (ESD). However, the entanglement under the weak measurement and reversal operation is always much stronger than the entanglement undergoing the amplitude damping decoherence. These results reflect that entanglement of two-qubit X-states from amplitude damping decoherence can be protected, and ESD can be circumvented by increasing the weak measurement strength.
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
Small slot waveguide rings for on-chip quantum optical circuits
Rotenberg, Nir; Haakh, Harald; Martin-Cano, Deigo; Goetzinger, Stephan; Sandoghdar, Vahid
2016-01-01
Nanophotonic interfaces between single emitters and light promise to enable new quantum optical technologies. Here, we use a combination of finite element simulations and analytic quantum theory to investigate the interaction of various quantum emitters with slot-waveguide rings. We predict that for rings with radii as small as 1.44 $\\mu$m (Q = 27,900), near-unity emitter-waveguide coupling efficiencies and emission enhancements on the order of 1300 can be achieved. By tuning the ring geometry or introducing losses, we show that realistic emitter-ring systems can be made to be either weakly or strongly coupled, so that we can observe Rabi oscillations in the decay dynamics even for micron-sized rings. Moreover, we demonstrate that slot waveguide rings can be used to directionally couple emission, again with near-unity efficiency. Our results pave the way for integrated solid-state quantum circuits involving various emitters.
Few-electron quantum dot circuit with integrated charge read out
Elzerman, J. M.; Hanson, R.; Greidanus, J. S.; Willems van Beveren, L. H.; de Franceschi, S.; Vandersypen, L. M.; Tarucha, S.; Kouwenhoven, L. P.
2003-04-01
We report on the realization of a few-electron double quantum dot defined in a two-dimensional electron gas by means of surface gates on top of a GaAs/AlGaAs heterostructure. Two quantum point contacts are placed in the vicinity of the double quantum dot and serve as charge detectors. These enable determination of the number of conduction electrons on each dot. This number can be reduced to zero, while still allowing transport measurements through the double dot. Microwave radiation is used to pump an electron from one dot to the other by absorption of a single photon. The experiments demonstrate that this quantum dot circuit can serve as a good starting point for a scalable spin-qubit system.
Efficient transfer of an arbitrary qutrit state in circuit quantum electrodynamics.
Liu, Tong; Xiong, Shao-Jie; Cao, Xiao-Zhi; Su, Qi-Ping; Yang, Chui-Ping
2015-12-01
Compared with a qubit, a qutrit (i.e., three-level quantum system) has a larger Hilbert space and thus can be used to encode more information in quantum information processing and communication. Here, we propose a method to transfer an arbitrary quantum state between two flux qutrits coupled to two resonators. This scheme is simple because it only requires two basic operations. The state-transfer operation can be performed fast because only resonant interactions are used. Numerical simulations show that the high-fidelity transfer of quantum states between the two qutrits is feasible with current circuit-QED technology. This scheme is quite general and can be applied to accomplish the same task for other solid-state qutrits coupled to resonators.
Theory of quantum-circuit refrigeration by photon-assisted electron tunneling
Silveri, Matti; Grabert, Hermann; Masuda, Shumpei; Tan, Kuan Yen; Möttönen, Mikko
2017-09-01
We focus on a recently experimentally realized scenario of normal-metal-insulator-superconductor tunnel junctions coupled to a superconducting resonator. We develop a first-principles theory to describe the effect of photon-assisted electron tunneling on the quantum state of the resonator. Our results are in very good quantitative agreement with the previous experiments on refrigeration and heating of the resonator using the photon-assisted tunneling, thus providing a stringent verification of the developed theory. Importantly, our results provide simple analytical estimates of the voltage-tunable coupling strength and temperature of the thermal reservoir formed by the photon-assisted tunneling. Consequently, they are used to introduce optimization principles for initialization of quantum devices using such a quantum-circuit refrigerator. Thanks to the first-principles nature of our approach, extension of the theory to the full spectrum of quantum electric devices seems plausible.
A Novel Implementation of Efficient Algorithms for Quantum Circuit Synthesis
Zeller, Luke
In this project, we design and develop a computer program to effectively approximate arbitrary quantum gates using the discrete set of Clifford Gates together with the T gate (π/8 gate). Employing recent results from Mosca et. al. and Giles and Selinger, we implement a decomposition scheme that outputs a sequence of Clifford, T, and Tt gates that approximate the input to within a specified error range ɛ. Specifically, the given gate is first rounded to an element of Z[1/2, i] with a precision determined by ɛ, and then exact synthesis is employed to produce the resulting gate. It is known that this procedure is optimal in approximating an arbitrary single qubit gate. Our program, written in Matlab and Python, can complete both approximate and exact synthesis of qubits. It can be used to assist in the experimental implementation of an arbitrary fault-tolerant single qubit gate, for which direct implementation isn't feasible.
Applications of the Fokker-Planck equation in circuit quantum electrodynamics
Elliott, Matthew; Ginossar, Eran
2016-10-01
We study exact solutions of the steady-state behavior of several nonlinear open quantum systems which can be applied to the field of circuit quantum electrodynamics. Using Fokker-Planck equations in the generalized P representation, we investigate the analytical solutions of two fundamental models. First, we solve for the steady-state response of a linear cavity that is coupled to an approximate transmon qubit and use this solution to study both the weak and strong driving regimes, using analytical expressions for the moments of both cavity and transmon fields, along with the Husimi Q function for the transmon. Second, we revist exact solutions of a quantum Duffing oscillator, which is driven both coherently and parametrically while also experiencing decoherence by the loss of single photons and pairs of photons. We use this solution to discuss both stabilization of Schrödinger cat states and the generation of squeezed states in parametric amplifiers, in addition to studying the Q functions of the different phases of the quantum system. The field of superconducting circuits, with its strong nonlinearities and couplings, has provided access to parameter regimes in which returning to these exact quantum optics methods can provide valuable insights.
Quantum Bayesian rule for weak measurements of qubits in superconducting circuit QED
Wang, Peiyue; Qin, Lupei; Li, Xin-Qi
2014-12-01
Compared with the quantum trajectory equation (QTE), the quantum Bayesian approach has the advantage of being more efficient to infer a quantum state under monitoring, based on the integrated output of measurements. For weak measurement of qubits in circuit quantum electrodynamics (cQED), properly accounting for the measurement backaction effects within the Bayesian framework is an important problem of current interest. Elegant work towards this task was carried out by Korotkov in ‘bad-cavity’ and weak-response limits (Korotkov 2011 Quantum Bayesian approach to circuit QED measurement (arXiv:1111.4016)). In the present work, based on insights from the cavity-field states (dynamics) and the help of an effective QTE, we generalize the results of Korotkov to more general system parameters. The obtained Bayesian rule is in full agreement with Korotkov's result in limiting cases and as well holds satisfactory accuracy in non-limiting cases in comparison with the QTE simulations. We expect the proposed Bayesian rule to be useful for future cQED measurement and control experiments.
Controllable cross-Kerr interaction between microwave photons in circuit quantum electrodynamics
Institute of Scientific and Technical Information of China (English)
Wu Qin-Qin; Liao Jie-Qiao; Kuang Le-Man
2011-01-01
We propose a scheme to enable a controllable cross-Kerr interaction between microwave photons in a circuit quantum electrodynamics (QED) system. In this scheme we use two transmission-line resonators (TLRs) and one superconducting quantum interference device (SQUID) type charge qubit, which acts as an artificial atom. It is shown that in the dispersive regime of the circuit-QED system, a controllable cross-Kerr interaction can be obtained by properly preparing the initial state of the qubit, and a large cross-phase shift between two microwave fields in the two TLRs can then be reached. Based on this cross-Kerr interaction, we show how to create a macroscopic entangled state between the two TLRs.
A twofold quantum delayed-choice experiment in a superconducting circuit.
Liu, Ke; Xu, Yuan; Wang, Weiting; Zheng, Shi-Biao; Roy, Tanay; Kundu, Suman; Chand, Madhavi; Ranadive, Arpit; Vijay, Rajamani; Song, Yipu; Duan, Luming; Sun, Luyan
2017-05-01
Wave-particle complementarity lies at the heart of quantum mechanics. To illustrate this mysterious feature, Wheeler proposed the delayed-choice experiment, where a quantum system manifests the wave- or particle-like attribute, depending on the experimental arrangement, which is made after the system has entered the interferometer. In recent quantum delayed-choice experiments, these two complementary behaviors were simultaneously observed with a quantum interferometer in a superposition of being closed and open. We suggest and implement a conceptually different quantum delayed-choice experiment by introducing a which-path detector (WPD) that can simultaneously record and neglect the system's path information, but where the interferometer itself is classical. Our experiment is realized with a superconducting circuit, where a cavity acts as the WPD for an interfering qubit. Using this setup, we implement the first twofold delayed-choice experiment, which demonstrates that the system's behavior depends not only on the measuring device's configuration that can be chosen even after the system has been detected but also on whether we a posteriori erase or mark the which-path information, the latter of which cannot be revealed by previous quantum delayed-choice experiments. Our results represent the first demonstration of both counterintuitive features with the same experimental setup, significantly extending the concept of quantum delayed-choice experiment.
A novel protection layer of superconducting microwave circuits toward a hybrid quantum system
Lee, Jongmin
2014-01-01
We propose a novel multilayer structure based on Bragg layers that can protect a superconducting microwave resonator from photons and blackbody radiation and have little effect on its quality factor. We also discuss a hybrid quantum system exploiting a superconducting microwave circuit and a two-color evanescent field atom trap, where surface-scattered photons and absorption-induced broadband blackbody radiation might deteriorate the system.
National Research Council Canada - National Science Library
ZHao, Hong-Quan; Kasai, Seiya
2012-01-01
.... Binary-decision-diagram- (BDD-) based arithmetic logic unit (ALU) is realized on GaAs-based regular nanowire network with hexagonal topology by the same fabrication method as that of the quantum devices and basic circuits...
Block-Z X Z synthesis of an arbitrary quantum circuit
De Vos, A.; De Baerdemacker, S.
2016-11-01
Given an arbitrary 2w×2w unitary matrix U , a powerful matrix decomposition can be applied, leading to four different syntheses of a w -qubit quantum circuit performing the unitary transformation. The demonstration is based on a recent theorem by H. Führ and Z. Rzeszotnik [Linear Algebra Its Appl. 484, 86 (2015), 10.1016/j.laa.2015.06.019] generalizing the scaling of single-bit unitary gates (w =1 ) to gates with arbitrary value of w . The synthesized circuit consists of controlled one-qubit gates, such as negator gates and phasor gates. Interestingly, the approach reduces to a known synthesis method for classical logic circuits consisting of controlled not gates in the case that U is a permutation matrix.
Multiphoton Interference in Quantum Fourier Transform Circuits and Applications to Quantum Metrology
Su, Zu-En; Li, Yuan; Rohde, Peter P.; Huang, He-Liang; Wang, Xi-Lin; Li, Li; Liu, Nai-Le; Dowling, Jonathan P.; Lu, Chao-Yang; Pan, Jian-Wei
2017-08-01
Quantum Fourier transforms (QFTs) have gained increased attention with the rise of quantum walks, boson sampling, and quantum metrology. Here, we present and demonstrate a general technique that simplifies the construction of QFT interferometers using both path and polarization modes. On that basis, we first observe the generalized Hong-Ou-Mandel effect with up to four photons. Furthermore, we directly exploit number-path entanglement generated in these QFT interferometers and demonstrate optical phase supersensitivities deterministically.
Complete Characterization of a Quantum Process: The Two-Bit Quantum Gate
Energy Technology Data Exchange (ETDEWEB)
Poyatos, J.; Cirac, J. [Departamento de Fisica Aplicada, Universidad de Castilla-La Mancha, 13071 Ciudad Real (Spain); Zoller, P. [Institut fuer Theoretisch Physik, Universitaet Innsbruck, A-6020, Innsbruck (Austria)
1997-01-01
We show how to fully characterize a quantum process in an open quantum system. We particularize the procedure to the case of a universal two-qubit gate in a quantum computer. We illustrate the method with a numerical simulation of a quantum gate in the ion trap quantum computer. {copyright} {ital 1997} {ital The American Physical Society}
Complete Characterization of a Quantum Process the Two-Bit Quantum Gate
Poyatos, J F; Zoller, P
1997-01-01
We show how to fully characterize a quantum process in an open quantum system. We particularize the procedure to the case of a universal two-qubit gate in a quantum computer. We illustrate the method with a numerical simulation of a quantum gate in the ion trap quantum computer.
Jakobczyk, L
2004-01-01
It is shown that even if the linear entropy of mixed two-qubit state is not smaller then 0.457, Bell - CHSH inequalities can be violated. This contradicts the result obtained in the paper of E. Santos [1].
Universal adiabatic quantum computation via the space-time circuit-to-Hamiltonian construction.
Gosset, David; Terhal, Barbara M; Vershynina, Anna
2015-04-10
We show how to perform universal adiabatic quantum computation using a Hamiltonian which describes a set of particles with local interactions on a two-dimensional grid. A single parameter in the Hamiltonian is adiabatically changed as a function of time to simulate the quantum circuit. We bound the eigenvalue gap above the unique ground state by mapping our model onto the ferromagnetic XXZ chain with kink boundary conditions; the gap of this spin chain was computed exactly by Koma and Nachtergaele using its q-deformed version of SU(2) symmetry. We also discuss a related time-independent Hamiltonian which was shown by Janzing to be capable of universal computation. We observe that in the limit of large system size, the time evolution is equivalent to the exactly solvable quantum walk on Young's lattice.
Cross-Kerr-effect induced by coupled Josephson qubits in circuit quantum electrodynamics
Energy Technology Data Exchange (ETDEWEB)
Hu Yong; Ge Guoqin; Chen Shi; Yang Xiaofei; Chen Youling [School of Physics, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Department of Electronic Science and Technology, Huazhong University of Science and Technology, Wuhan, Hubei 430074 (China); Department of Physics, Peking University, Beijing 100871 (China)
2011-07-15
We propose a scheme for implementing cross-Kerr nonlinearity between two superconducting transmission line resonators (TLRs) via their interactions with a coupler constructed by two superconducting transmon qubits connected to each other through a superconducting quantum interference device. When suitably driven, the coupler can induce very strong cross phase modulation (XPM) between the two TLRs due to its N-type level structure and the consequent electromagnetically induced transparency in its lowest states. The flexibility of our design can lead to various inter-TLR coupling configurations. The obtained cross-Kerr coefficient is large enough to allow many important quantum operations in which only few photons are involved. We further show that this scheme is very robust against fluctuations in solid-state quantum circuits. Our numerical calculations imply that the absorption and the dispersion of the TLRs resulting from the decoherence of the coupler are very small compared with the proposed XPM strength.
Two mode photon bunching effect as witness of quantum criticality in circuit QED
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
We suggest a scheme to probe critical phenomena at a quantum phase transition (QPT) using the quantum correlation of two photonic modes simultaneously coupled to a critical system. As an experimentally accessible physical implementation,a circuit QED system is formed by a capacitively coupled Josephson junction qubit array interacting with one superconducting transmission line resonator (TLR). It realizes an Ising chain in the transverse field (ICTF) which interacts with the two magnetic modes propagating in the TLR. We demonstrate that in the vicinity of criticality the originally independent fields tend to display photon bunching effects due to their interaction with the ICTF. Thus,the occurrence of the QPT is reflected by the quantum characteristics of the photonic fields.
Two mode photon bunching effect as witness of quantum criticality in circuit QED
Institute of Scientific and Technical Information of China (English)
AI Qing; WANG YingDan; LONG GuiLu; SUN ChangPu
2009-01-01
We suggest a scheme to probe critical phenomena at a quantum phase transition (OPT) using the quantum correlation of two photonic modes simultaneously coupled to a critical system. As an experimentally accessible physical implementation, a circuit QED system is formed by a capsciUvely coupled Josephson junction qubit array interacting with one superconducting transmission line resonator (TLR). It realizes an Ising chain in the transverse field (ICTF) which interacts with the two magnetic modes propagating in the TLR. We demonstrate that in the vicinity of criticality the originally independent fields tend to display photon bunching effects due to their interaction with the ICTF. Thus,the occurrence of the QPT is reflected by the quantum characteristics of the photonic fields.
Waveguide photon-number-resolving detectors for quantum photonic integrated circuits
Sahin, D; Zhou, Z; Jahanmirinejad, S; Mattioli, F; Leoni, R; Beetz, J; Lermer, M; Kamp, M; Höfling, S; Fiore, A
2013-01-01
Quantum photonic integration circuits are a promising approach to scalable quantum processing with photons. Waveguide single-photon-detectors (WSPDs) based on superconducting nanowires have been recently shown to be compatible with single-photon sources for a monolithic integration. While standard WSPDs offer single-photon sensitivity, more complex superconducting nanowire structures can be configured to have photon-number-resolving capability. In this work, we present waveguide photon-number-resolving detectors (WPNRDs) on GaAs/Al0.75Ga0.25As ridge waveguides based on a series connection of nanowires. The detection of 0-4 photons has been demonstrated with a four-wire WPNRD, having a single electrical read-out. A device quantum efficiency ~24 % is reported at 1310 nm for the TE polarization.
Fast universal quantum gates on microwave photons with all-resonance operations in circuit QED.
Hua, Ming; Tao, Ming-Jie; Deng, Fu-Guo
2015-03-19
Stark shift on a superconducting qubit in circuit quantum electrodynamics (QED) has been used to construct universal quantum entangling gates on superconducting resonators in previous works. It is a second-order coupling effect between the resonator and the qubit in the dispersive regime, which leads to a slow state-selective rotation on the qubit. Here, we present two proposals to construct the fast universal quantum gates on superconducting resonators in a microwave-photon quantum processor composed of multiple superconducting resonators coupled to a superconducting transmon qutrit, that is, the controlled-phase (c-phase) gate on two microwave-photon resonators and the controlled-controlled phase (cc-phase) gates on three resonators, resorting to quantum resonance operations, without any drive field. Compared with previous works, our universal quantum gates have the higher fidelities and shorter operation times in theory. The numerical simulation shows that the fidelity of our c-phase gate is 99.57% within about 38.1 ns and that of our cc-phase gate is 99.25% within about 73.3 ns.
A circuit QED controlled-Z ``AMP'' gate (Adiabatic MultiPole gate)
McKay, David C.; Naik, Ravi; Bishop, Lev S.; Schuster, David I.
2014-03-01
Circuit quantum electrodynamics -- superconducting Josephson junction ``transmon'' qubits coupled via microwave cavities -- is a promising route towards scalable quantum computing. Here we report on experiments coupling two transmon qubits through multiple strongly coupled planar superconducting cavities -- the multipole cavity QED architecture. This design enables large interactions (mediated by real cavity photons) when the transmons are resonant with the cavities, and low off rates when the qubits are tuned away from the cavity resonance. In this talk we will discuss our gate protocol -- the AMP gate -- and report on producing a high fidelity Bell state (| gg > + | ee >) measured from state and process tomography. We will discuss future plans for scaling this architecture beyond two qubits.
Linear optics and quantum maps
Aiello, A; Woerdman, J P
2006-01-01
We present a theoretical analysis of the connection between classical polarization optics and quantum mechanics of two-level systems. First, we review the matrix formalism of classical polarization optics from a quantum information perspective. In this manner the passage from the Stokes-Jones-Mueller description of classical optical processes to the representation of one- and two-qubit quantum operations, becomes straightforward. Second, as a practical application of our classical-\\emph{vs}-quantum formalism, we show how two-qubit maximally entangled mixed states (MEMS), can be generated by using polarization and spatial modes of photons generated via spontaneous parametric down conversion.
Guo-Hui, Yang; Le, Song
2016-02-01
By taking into account the Dzyaloshinsky-Moriya (DM) interaction under uniform magnetic field, quantum correlation behaviors measured by the measurement-induced nonlocality (MIN) and the geometric measure of discord (GMOD) in a two-qubit XY model are investigated in detail. Turning the different parameters can lead the two kinds of measurements to present different properties. For example, increasing the parameter B(uniform magnetic field), the existing region of MIN is larger than GMOD; MIN can appear the phenomenon of monotonous reduction when the parameter D(Dzyaloshinsky-Moriya interaction) is smaller than one threshold value, while GMOD cannot; MIN monotonously reduces with enhancive value of T(temperature), while GMOD initial experiences a slightly increasing and then decreases. One interesting point is that the more obvious and complicated difference between them are shown from the initial values. This property is both true for the zero temperature and the finite temperature. Through analyzing the limit case of the temperature approaching zero, the analytic solutions give the detailed reasons why have different effect on the initial values. Moreover, from the analytic solutions, we know the initial value of MIN is always larger than or equal to GMOD.
Energy Technology Data Exchange (ETDEWEB)
Rossi, Matteo A. C., E-mail: matteo.rossi@unimi.it [Quantum Technology Lab, Dipartimento di Fisica, Università degli Studi di Milano, 20133 Milano (Italy); Paris, Matteo G. A., E-mail: matteo.paris@fisica.unimi.it [Quantum Technology Lab, Dipartimento di Fisica, Università degli Studi di Milano, 20133 Milano (Italy); CNISM, Unità Milano Statale, I-20133 Milano (Italy)
2016-01-14
We address the interaction of single- and two-qubit systems with an external transverse fluctuating field and analyze in detail the dynamical decoherence induced by Gaussian noise and random telegraph noise (RTN). Upon exploiting the exact RTN solution of the time-dependent von Neumann equation, we analyze in detail the behavior of quantum correlations and prove the non-Markovianity of the dynamical map in the full parameter range, i.e., for either fast or slow noise. The dynamics induced by Gaussian noise is studied numerically and compared to the RTN solution, showing the existence of (state dependent) regions of the parameter space where the two noises lead to very similar dynamics. We show that the effects of RTN noise and of Gaussian noise are different, i.e., the spectrum alone is not enough to summarize the noise effects, but the dynamics under the effect of one kind of noise may be simulated with high fidelity by the other one.
Yamada, Takahiro; Maezawa, Masaaki; Urano, Chiharu
2015-11-01
We present design and testing of a pseudo-random number generator (PRNG) and a variable pulse number multiplier (VPNM) which are digital circuit subsystems in an integrated quantum voltage noise source for Jonson noise thermometry. Well-defined, calculable pseudo-random patterns of single flux quantum pulses are synthesized with the PRNG and multiplied digitally with the VPNM. The circuit implementation on rapid single flux quantum technology required practical circuit scales and bias currents, 279 junctions and 33 mA for the PRNG, and 1677 junctions and 218 mA for the VPNM. We confirmed the circuit operation with sufficiently wide margins, 80-120%, with respect to the designed bias currents.
Quantum dynamics of a two-atom-qubit system
Energy Technology Data Exchange (ETDEWEB)
Nguyen Van Hieu; Nguyen Bich Ha [Max-Planck Institute for the Physics of Complex Systems, Noethnitzer Str. 38, D-01187 Dresden (Germany); Le Thi Ha Linh [Institute of Materials Science, Vietnam Academy of Science and Technology, 18 Hoang Quoc Viet, Cau Giay, Hanoi (Viet Nam)], E-mail: nvhieu@iop.vast.ac.vn
2009-09-01
A physical model of the quantum information exchange between two qubits is studied theoretically. The qubits are two identical two-level atoms, the physical mechanism of the quantum information exchange is the mutual dependence of the reduced density matrices of two qubits generated by their couplings with a multimode radiation field. The Lehmberg-Agarwal master equation is exactly solved. The explicit form of the mutual dependence of two reduced density matrices is established. The application to study the entanglement of two qubits is discussed.
Institute of Scientific and Technical Information of China (English)
Yang Bai-Yuan; Fang Mao-Fa; Huang Jiang
2013-01-01
In this paper,the dynamical behavior of entanglement of an uncoupled two-qubit system,which interacts with independent identical amplitude damping environments and is initially prepared in the extended Werner-like (EWL) states,is investigated.The results show that whether entanglement sudden death (ESD) of an EWL state will occur or not depends on initial purity and concurrence.The boundaries between ESD states and ESD-free states for two kinds of EWL states are found to be different.Furthermore,some regions are shown where ESD states can be transformed into ESD-free states by local unitary operations.
Decoherence of Two-qubits Coupled with Reservoirs Studied with New Ket-Bra Entangled State Method
Ren, Yi-Chong; Fan, Hong-Yi
2016-04-01
For the first time we define a so-called Ket-Bra Entangled State (KBES) for two-qubits coupled with reservoirs by introduce an extra fictitious mode vector, and convert the corresponding master equation into Schrödinger-like equation by virtue of this state. Via this approach we concisely obtain the dynamic evolution of two uncoupled qubits each immersed in local thermal noise. Based on this, the decoherence evolution for the extended Werner-like states is derived and how purity and temperature influence the concurrence is analyzed. This KBES method may also be applied to tackling master equations of limited atomic level systems.
Hardware-Efficient and Fully Autonomous Quantum Error Correction in Superconducting Circuits
Kapit, Eliot
2016-04-01
Superconducting qubits are among the most promising platforms for building a quantum computer. However, individual qubit coherence times are not far past the scalability threshold for quantum error correction, meaning that millions of physical devices would be required to construct a useful quantum computer. Consequently, further increases in coherence time are very desirable. In this Letter, we blueprint a simple circuit consisting of two transmon qubits and two additional lossy qubits or resonators, which is passively protected against all single-qubit quantum error channels through a combination of continuous driving and engineered dissipation. Photon losses are rapidly corrected through two-photon drive fields implemented with driven superconducting quantum interference device couplings, and dephasing from random potential fluctuations is heavily suppressed by the drive fields used to implement the multiqubit Hamiltonian. Comparing our theoretical model to published noise estimates from recent experiments on flux and transmon qubits, we find that logical state coherence could be improved by a factor of 40 or more compared to the individual qubit T1 and T2 using this technique. We thus demonstrate that there is substantial headroom for improving the coherence of modern superconducting qubits with a fairly modest increase in device complexity.
Hardware-Efficient and Fully Autonomous Quantum Error Correction in Superconducting Circuits.
Kapit, Eliot
2016-04-15
Superconducting qubits are among the most promising platforms for building a quantum computer. However, individual qubit coherence times are not far past the scalability threshold for quantum error correction, meaning that millions of physical devices would be required to construct a useful quantum computer. Consequently, further increases in coherence time are very desirable. In this Letter, we blueprint a simple circuit consisting of two transmon qubits and two additional lossy qubits or resonators, which is passively protected against all single-qubit quantum error channels through a combination of continuous driving and engineered dissipation. Photon losses are rapidly corrected through two-photon drive fields implemented with driven superconducting quantum interference device couplings, and dephasing from random potential fluctuations is heavily suppressed by the drive fields used to implement the multiqubit Hamiltonian. Comparing our theoretical model to published noise estimates from recent experiments on flux and transmon qubits, we find that logical state coherence could be improved by a factor of 40 or more compared to the individual qubit T_{1} and T_{2} using this technique. We thus demonstrate that there is substantial headroom for improving the coherence of modern superconducting qubits with a fairly modest increase in device complexity.
Gaudreau, Louis; Bogan, Alex; Korkusinski, Marek; Studenikin, Sergei; Austing, D. Guy; Sachrajda, Andrew S.
2017-09-01
Long distance entanglement distribution is an important problem for quantum information technologies to solve. Current optical schemes are known to have fundamental limitations. A coherent photon-to-spin interface built with quantum dots (QDs) in a direct bandgap semiconductor can provide a solution for efficient entanglement distribution. QD circuits offer integrated spin processing for full Bell state measurement (BSM) analysis and spin quantum memory. Crucially the photo-generated spins can be heralded by non-destructive charge detection techniques. We review current schemes to transfer a polarization-encoded state or a time-bin-encoded state of a photon to the state of a spin in a QD. The spin may be that of an electron or that of a hole. We describe adaptations of the original schemes to employ heavy holes which have a number of attractive properties including a g-factor that is tunable to zero for QDs in an appropriately oriented external magnetic field. We also introduce simple throughput scaling models to demonstrate the potential performance advantage of full BSM capability in a QD scheme, even when the quantum memory is imperfect, over optical schemes relying on linear optical elements and ensemble quantum memories.
Pairwise Quantum Correlations for Superpositions of Dicke States
Xi, Zhengjun; Li, Yongming; Wang, Xiaoguang
2011-01-01
Using the concept of quantum discord (QD), we study the quantum correlation for a class of two-qubit X states with exchange and parity symmetries, whose density matrices have complex off-diagonal elements. We derive an upper bound of the QD, which is independent of the arguments of the complex off-diagonal elements of the reduced two-qubit density matricies. Moreover, for the two-qubit X states obtained from Dicke states and their superposition states, we obtain a compact expression of the QD by numerical check. Finally, we apply the expression to discuss the quantum correlation of the reduced two-qubit states of Dicke states and their superpositions, and the results are compared with those obtained by entanglement of formation (EoF), which is a quantum entanglement measure.
Use of non-adiabatic geometric phase for quantum computing by NMR.
Das, Ranabir; Kumar, S K Karthick; Kumar, Anil
2005-12-01
Geometric phases have stimulated researchers for its potential applications in many areas of science. One of them is fault-tolerant quantum computation. A preliminary requisite of quantum computation is the implementation of controlled dynamics of qubits. In controlled dynamics, one qubit undergoes coherent evolution and acquires appropriate phase, depending on the state of other qubits. If the evolution is geometric, then the phase acquired depend only on the geometry of the path executed, and is robust against certain types of error. This phenomenon leads to an inherently fault-tolerant quantum computation. Here we suggest a technique of using non-adiabatic geometric phase for quantum computation, using selective excitation. In a two-qubit system, we selectively evolve a suitable subsystem where the control qubit is in state |1, through a closed circuit. By this evolution, the target qubit gains a phase controlled by the state of the control qubit. Using the non-adiabatic geometric phase we demonstrate implementation of Deutsch-Jozsa algorithm and Grover's search algorithm in a two-qubit system.
Three-observer Bell inequality violation on a two-qubit entangled state
Schiavon, Matteo; Calderaro, Luca; Pittaluga, Mirko; Vallone, Giuseppe; Villoresi, Paolo
2016-01-01
Bipartite Bell inequalities can be simultaneously violated by two different pairs of observers when weak measurements and signaling is employed. Here we experimentally demonstrate the violation of two simultaneous CHSH inequalities by exploiting a two-photon polarization maximally entangled state. Our results demonstrate that large double violation is experimentally achievable. Our demonstration may have impact for Quantum Key Distribution or certification of Quantum Random Number generators ...
Three-observer Bell inequality violation on a two-qubit entangled state
Schiavon, Matteo; Calderaro, Luca; Pittaluga, Mirko; Vallone, Giuseppe; Villoresi, Paolo
2017-03-01
Bipartite Bell inequalities can simultaneously be violated by two different pairs of observers when weak measurements and signalling is employed. Here, we experimentally demonstrate the violation of two simultaneous CHSH inequalities by exploiting a two-photon polarisation maximally entangled state. Our results demonstrate that large double violation is experimentally achievable. Our demonstration may have impact for Quantum Key Distribution or certification of Quantum Random Number generators based on weak measurements.
Experimental demonstration of a programmable quantum computer by NMR.
Kim, Jaehyun; Lee, Jae-Seung; Hwang, Taesoon; Lee, Soonchil
2004-01-01
A programmable quantum computer is experimentally demonstrated by nuclear magnetic resonance using one qubit for the program and two qubits for data. A non-separable two-qubit operation is performed in a programmable way to show the successful demonstration. Projective measurements required in the programmable quantum computer are simulated by averaging the results of experiments just like when producing an effective pure state.
Ulmer, W; Halberg, F; Schwarzkopff, O
2011-01-01
The existence of specific biorhythms and the role of geomagnetic and/or solar magnetic activities are well-established by appropriate correlations in chronobiology. From a physical viewpoint, there are two different accesses to biorhythms to set up connections to molecular processes: 1. Diffusion of charged molecules in magnetic fields. 2. Quantum mechanical perturbation theoretical methods and their resonance dominators to characterize specific interactions between constituents. The methods of point 2 permit the treatment of molecular processes by circuits with characteristic resonances and 'beat-frequencies', which result from the primarily fast physical processes. As examples the tunneling processes between DNA base pairs (H bonds) and the ATP decomposition are considered.
Quintana, C. M.; Megrant, A.; Chen, Z.; Dunsworth, A.; Chiaro, B.; Barends, R.; Campbell, B.; Chen, Yu; Hoi, I.-C.; Jeffrey, E.; Kelly, J.; Mutus, J. Y.; O'Malley, P. J. J.; Neill, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Cleland, A. N.; Martinis, John M.
2014-08-01
Many superconducting qubits are highly sensitive to dielectric loss, making the fabrication of coherent quantum circuits challenging. To elucidate this issue, we characterize the interfaces and surfaces of superconducting coplanar waveguide resonators and study the associated microwave loss. We show that contamination induced by traditional qubit lift-off processing is particularly detrimental to quality factors without proper substrate cleaning, while roughness plays at most a small role. Aggressive surface treatment is shown to damage the crystalline substrate and degrade resonator quality. We also introduce methods to characterize and remove ultra-thin resist residue, providing a way to quantify and minimize remnant sources of loss on device surfaces.
Energy Technology Data Exchange (ETDEWEB)
Quintana, C. M.; Megrant, A.; Chen, Z.; Dunsworth, A.; Chiaro, B.; Barends, R.; Campbell, B.; Chen, Yu; Hoi, I.-C.; Jeffrey, E.; Kelly, J.; Mutus, J. Y.; O' Malley, P. J. J.; Neill, C.; Roushan, P.; Sank, D.; Vainsencher, A.; Wenner, J.; White, T. C.; Cleland, A. N. [Department of Physics, University of California, Santa Barbara, California 93106 (United States); and others
2014-08-11
Many superconducting qubits are highly sensitive to dielectric loss, making the fabrication of coherent quantum circuits challenging. To elucidate this issue, we characterize the interfaces and surfaces of superconducting coplanar waveguide resonators and study the associated microwave loss. We show that contamination induced by traditional qubit lift-off processing is particularly detrimental to quality factors without proper substrate cleaning, while roughness plays at most a small role. Aggressive surface treatment is shown to damage the crystalline substrate and degrade resonator quality. We also introduce methods to characterize and remove ultra-thin resist residue, providing a way to quantify and minimize remnant sources of loss on device surfaces.
Designing quantum-dot cellular automata circuits using a robust one layer crossover scheme
Directory of Open Access Journals (Sweden)
Sara Hashemi
2014-04-01
Full Text Available Quantum-dot cellular automata (QCA is a novel nanotechnology which is considered as a solution to the scaling problems in complementary metal oxide semiconductor technology. In this Letter, a robust one layer crossover scheme is introduced. It uses only 90° QCA cells and works based on a proper clock assignment. The application of this new scheme is shown in designing a sample QCA circuit. Simulation results demonstrate that using this new scheme, significant improvements in terms of area and complexity can be achieved.
Mesoscopic entangled coherent states implemented with a circuit quantum electrodynamics system
Institute of Scientific and Technical Information of China (English)
Zhao Ying-Yan; Jiang Nian-Quan
2013-01-01
We show a scheme to generate entangled coherent states in a circuit quantum electrodynamics system,which consists of a nanomechanical resonator,a superconducting Cooper-pair box (CPB),and a superconducting transmission line resonator.In the system,the CPB plays the role of a nonlinear medium and can be conveniently controlled by a gate voltage including direct-current and alternating-current components.The scheme provides a powerful tool for preparing the multipartite mesoscopic entangled coherent states.
Lee, Minchul; Choi, Mahn-Soo
2014-08-15
We investigate the mesoscopic resistor-capacitor circuit consisting of a quantum dot coupled to spatially separated Majorana fermion modes in a chiral topological superconductor. We find substantially enhanced relaxation resistance due to the nature of Majorana fermions, which are their own antiparticles and are composed of particle and hole excitations in the same abundance. Further, if only a single Majorana mode is involved, the zero-frequency relaxation resistance is completely suppressed due to a destructive interference. As a result, the Majorana mode opens an exotic dissipative channel on a superconductor which is typically regarded as dissipationless due to its finite superconducting gap.
Advances in quantum control of three-level superconducting circuit architectures
Energy Technology Data Exchange (ETDEWEB)
Falci, G.; Paladino, E. [Dipartimento di Fisica e Astronomia, Universita di Catania (Italy); CNR-IMM UOS Universita (MATIS), Consiglio Nazionale delle Ricerche, Catania (Italy); INFN, Sezione di Catania (Italy); Di Stefano, P.G. [Dipartimento di Fisica e Astronomia, Universita di Catania (Italy); Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Queen' s University Belfast(United Kingdom); Ridolfo, A.; D' Arrigo, A. [Dipartimento di Fisica e Astronomia, Universita di Catania (Italy); Paraoanu, G.S. [Low Temperature Laboratory, Department of Applied Physics, Aalto University School of Science (Finland)
2017-06-15
Advanced control in Lambda (Λ) scheme of a solid state architecture of artificial atoms and quantized modes would allow the translation to the solid-state realm of a whole class of phenomena from quantum optics, thus exploiting new physics emerging in larger integrated quantum networks and for stronger couplings. However control solid-state devices has constraints coming from selection rules, due to symmetries which on the other hand yield protection from decoherence, and from design issues, for instance that coupling to microwave cavities is not directly switchable. We present two new schemes for the Λ-STIRAP control problem with the constraint of one or two classical driving fields being always-on. We show how these protocols are converted to apply to circuit-QED architectures. We finally illustrate an application to coherent spectroscopy of the so called ultrastrong atom-cavity coupling regime. (copyright 2016 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)
Landau-Zener-Stückelberg-Majorana lasing in circuit quantum electrodynamics
Neilinger, P.; Shevchenko, S. N.; Bogár, J.; Rehák, M.; Oelsner, G.; Karpov, D. S.; Hübner, U.; Astafiev, O.; Grajcar, M.; Il'ichev, E.
2016-09-01
We demonstrate amplification (and attenuation) of a probe signal by a driven two-level quantum system in the Landau-Zener-Stückelberg-Majorana regime by means of an experiment, in which a superconducting qubit was strongly coupled to a microwave cavity, in a conventional arrangement of circuit quantum electrodynamics. Two different types of flux qubit, specifically a conventional Josephson junctions qubit and a phase-slip qubit, show similar results, namely, lasing at the working points where amplification takes place. The experimental data are explained by the interaction of the probe signal with Rabi-like oscillations. The latter are created by constructive interference of Landau-Zener-Stückelberg-Majorana (LZSM) transitions during the driving period of the qubit. A detailed description of the occurrence of these oscillations and a comparison of obtained data with both analytic and numerical calculations are given.
Deterministic separation of arbitrary photon pair states in integrated quantum circuits
Marchildon, Ryan P
2015-01-01
Entangled photon pairs generated within integrated devices must often be spatially separated for their subsequent manipulation in quantum circuits. Separation that is both deterministic and universal can in principle be achieved through anti-coalescent two-photon quantum interference. However, such interference-facilitated pair separation (IFPS) has not been extensively studied in the integrated setting, where the strong polarization and wavelength dependencies of integrated couplers -- as opposed to bulk-optics beamsplitters -- can have important implications for performance beyond the identical-photon regime. This paper provides a detailed review of IFPS and examines how these dependencies impact separation fidelity and interference visibility. Focus is given to IFPS mediated by an integrated directional coupler. The analysis applies equally to both on-chip and in-fiber implementations, and can be expanded to other coupler architectures such as multimode interferometers. When coupler dispersion is present, ...
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.
Protected quantum computation with multiple resonators in ultrastrong coupling circuit QED
Nataf, Pierre
2011-01-01
We investigate theoretically the dynamical behavior of a qubit obtained with the two ground eigenstates of an ultrastrong coupling circuit-QED system consisting of a finite number of Josephson fluxonium atoms inductively coupled to a transmission line resonator. We show an universal set of quantum gates by using multiple transmission line resonators (each resonator represents a single qubit). We discuss the intrinsic 'anisotropic' nature of noise sources for fluxonium artificial atoms. Through a master equation treatment with colored noise and manylevel dynamics, we prove that, for a general class of anisotropic noise sources, the coherence time of the qubit and the fidelity of the quantum operations can be dramatically improved in an optimal regime of ultrastrong coupling, where the ground state is an entangled photonic 'cat' state.
Rapid single-flux-quantum circuits for low noise mK operation
Intiso, Samuel; Pekola, Jukka; Savin, Alexander; Devyatov, Ygor; Kidiyarova-Shevchenko, Anna
2006-05-01
Rapid single-flux-quantum (RSFQ) technology has been proposed as control electronics for superconducting quantum bits because of the material and working temperature compatibility. In this work, we consider practical aspects of RSFQ circuit design for low noise low power operation. At the working temperature of 20 mK and operational frequency of 2 GHz, dissipated power per junction is reduced to 25 pW by using 6 µA critical current junctions available at the Hypres and VTT low Jc fabrication process. To limit phonon temperature to 30 mK, a maximum of 40 junctions can be placed on a 5 mm × 5 mm chip. Electron temperature in resistive shunts of Josephson junctions is minimized by use of cooling fins, giving minimum electron temperatures of about 150 mK for the Hypres process and 70 mK for the VTT process.
Gain-assisted optical bistability and multistability in superconducting phase quantum circuits
Amini Sabegh, Z.; Maleki, M. A.; Mahmoudi, M.
2017-02-01
We study the absorption and optical bistability (OB) behavior of the superconducting phase quantum circuits in the four-level cascade and closed-loop configurations. It is shown that the OB is established in both configurations and it can be controlled by the intensity and frequency of applied fluxes. It is also demonstrated that the gain-assisted OB is generated in both configurations and can switch to the gain-assisted optical multistability (OM) only by changing the relative phase of applied fluxes in closed-loop quantum system. It is worth noting that the several significant output fluxes with negligible inputs can be seen in bistable behavior of the closed-loop configuration due to the nonlinear processing.
Nano-photonics in III-V semiconductors for integrated quantum optical circuits
Wasley, Nicholas Andrew
This thesis describes the optical spectroscopic measurements of III-V semiconductors used to investigate a number of issues related to the development of integrated quantum optical circuits. The disorder-limited propagation of photons in photonic crystal waveguides in the slow-light regime is investigated. The analysis of Fabry-Perot resonances is used to map the mode dispersion and extract the photon localisation length. Andersonlocalised modes are observed at high group indices, when the localisation lengths are shorter than the waveguide lengths, consistent with the Fabry-Perot analysis. A spin-photon interface based on two orthogonal waveguides is introduced, where the polarisation emitted by a quantum dot is mapped to a path-encoded photon. Operation is demonstrated by deducing the spin using the interference of in-plane photons. A second device directly maps right and left circular polarisations to anti-parallel waveguides, surprising for a non-chiral structure but consistent with an off-centre dot. Two dimensional photonic crystal cavities in GaInP and full control over the spontaneous emission rate of InP quantum dots is demonstrated by spectrally tuning the exciton emission energy into resonance with the fundamental cavity mode. Fourier transform spectroscopy is used to investigate the short coherence times of InP quantum dots in GaInP photonic crystal cavities. Additional technological developments are also presented including a quantum dot registration technique, electrical tuning of quantum dot emission and uniaxial strain tuning of H1 cavity modes.
Exact stabilization of entangled states in finite time by dissipative quantum circuits
Johnson, Peter D.; Ticozzi, Francesco; Viola, Lorenza
2017-07-01
Open quantum systems evolving according to discrete-time dynamics are capable, unlike continuous-time counterparts, to converge to a stable equilibrium in finite time with zero error. We consider dissipative quantum circuits consisting of sequences of quantum channels subject to specified quasi-locality constraints, and determine conditions under which stabilization of a pure multipartite entangled state of interest may be exactly achieved in finite time. Special emphasis is devoted to characterizing scenarios where finite-time stabilization may be achieved robustly with respect to the order of the applied quantum maps, as suitable for unsupervised control architectures. We show that if a decomposition of the physical Hilbert space into virtual subsystems is found, which is compatible with the locality constraint and relative to which the target state factorizes, then robust stabilization may be achieved by independently cooling each component. We further show that if the same condition holds for a scalable class of pure states, a continuous-time quasi-local Markov semigroup ensuring rapid mixing can be obtained. Somewhat surprisingly, we find that the commutativity of the canonical parent Hamiltonian one may associate to the target state does not directly relate to its finite-time stabilizability properties, although in all cases where we can guarantee robust stabilization, a (possibly noncanonical) commuting parent Hamiltonian may be found. Aside from graph states, quantum states amenable to finite-time robust stabilization include a class of universal resource states displaying two-dimensional symmetry-protected topological order, along with tensor network states obtained by generalizing a construction due to Bravyi and Vyalyi [Quantum Inf. Comput. 5, 187 (2005)]. Extensions to representative classes of mixed graph-product and thermal states are also discussed.
Circuit quantum electrodynamics architecture for gate-defined quantum dots in silicon
Mi, X.; Cady, J. V.; Zajac, D. M.; Stehlik, J.; Edge, L. F.; Petta, J. R.
2017-01-01
We demonstrate a hybrid device architecture where the charge states in a double quantum dot (DQD) formed in a Si/SiGe heterostructure are read out using an on-chip superconducting microwave cavity. A quality factor Q = 5400 is achieved by selectively etching away regions of the quantum well and by reducing photon losses through low-pass filtering of the gate bias lines. Homodyne measurements of the cavity transmission reveal DQD charge stability diagrams and a charge-cavity coupling rate gc/2 π= 23 MHz. These measurements indicate that electrons trapped in a Si DQD can be effectively coupled to microwave photons, potentially enabling coherent electron-photon interactions in silicon.
Enhanced Open-Circuit Voltage of PbS Nanocrystal Quantum Dot Solar Cells
Yoon, Woojun; Boercker, Janice E.; Lumb, Matthew P.; Placencia, Diogenes; Foos, Edward E.; Tischler, Joseph G.
2013-07-01
Nanocrystal quantum dots (QD) show great promise toward improving solar cell efficiencies through the use of quantum confinement to tune absorbance across the solar spectrum and enable multi-exciton generation. Despite this remarkable potential for high photocurrent generation, the achievable open-circuit voltage (Voc) is fundamentally limited due to non-radiative recombination processes in QD solar cells. Here we report the highest open-circuit voltages to date for colloidal QD based solar cells under one sun illumination. This Voc of 692 +/- 7 mV for 1.4 eV PbS QDs is a result of improved passivation of the defective QD surface, demonstrating as a function of the QD bandgap (Eg). Comparing experimental Voc variation with the theoretical upper-limit obtained from one diode modeling of the cells with different Eg, these results clearly demonstrate that there is a tremendous opportunity for improvement of Voc to values greater than 1 V by using smaller QDs in QD solar cells.
Disentanglement of Two Qubits Coupled to an XY Spin Chain at Finite Temperature
Institute of Scientific and Technical Information of China (English)
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.
Energy Technology Data Exchange (ETDEWEB)
Yamada, Takahiro, E-mail: yamada-takahiro@aist.go.jp [Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology, Central 2, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568 (Japan); Maezawa, Masaaki [Nanoelectronics Research Institute, National Institute of Advanced Industrial Science and Technology, Central 2, Umezono 1-1-1, Tsukuba, Ibaraki 305-8568 (Japan); Urano, Chiharu [National Metrology Institute of Japan, National Institute of Advanced Industrial Science and Technology, Central 3, Umezono 1-1-1, Tsukuba, Ibaraki 305-8563 (Japan)
2015-11-15
Highlights: • We demonstrated RSFQ digital components of a new quantum voltage noise source. • A pseudo-random number generator and variable pulse number multiplier are designed. • Fabrication process is based on four Nb wiring layers and Nb/AlOx/Nb junctions. • The circuits successfully operated with wide dc bias current margins, 80–120%. - Abstract: We present design and testing of a pseudo-random number generator (PRNG) and a variable pulse number multiplier (VPNM) which are digital circuit subsystems in an integrated quantum voltage noise source for Jonson noise thermometry. Well-defined, calculable pseudo-random patterns of single flux quantum pulses are synthesized with the PRNG and multiplied digitally with the VPNM. The circuit implementation on rapid single flux quantum technology required practical circuit scales and bias currents, 279 junctions and 33 mA for the PRNG, and 1677 junctions and 218 mA for the VPNM. We confirmed the circuit operation with sufficiently wide margins, 80–120%, with respect to the designed bias currents.
Institute of Scientific and Technical Information of China (English)
吴春旺; 韩阳; 邓志姣; 李虹轶; 陈平形; 李承祖
2011-01-01
We propose a theoretical scheme for realizing the general conditional phase shift gate of charge qubits situated in a high-Q superconducting transmission line resonator. The phase shifting angle can be tuned from 0 to 27r by simply adjusting the qubit-resonator detuning and the interaction time. Based on this gate proposal, we give a detailed procedure to implement the three-qubit quantum Fourier transform with circuit quantum eleetrodynamics （QED）. A careful analysis of the decoherence sources shows that the algorithm can be achieved with a high fidelity using current circuit QED techniques.
Quantum Correlations in Heisenberg XY Chain
Institute of Scientific and Technical Information of China (English)
ZHU Yin-Yan; ZHANG Yong
2013-01-01
Quantum correlations measured by quantum discord (QD),measurement-induced distance (MID),and geometric measure of quantum discord (GMQD) in two-qubit Heisenberg XY spin chain are investigated.The effects of DM interaction and anisotropic on the three correlations are considered.Characteristics of various correlation measures for the two-qubit states are compared.The increasing Dz increases QD,MID and GMQD monotonously while the increasing anisotropy both increases and decreases QD and GMQD.The three quantum correlations are always existent at very high temperature.MID is always larger than QD,but there is no definite ordering between QD and GMQD.
Institute of Scientific and Technical Information of China (English)
Xu Xiao-Bo; Liu Jin-Ming; Yu Peng-Fei
2008-01-01
Taking the intrinsic decoherence effect into account,this paper investigates the entanglement of a two-qubit anisotropic Heisenberg XY Z model in the presence of nonuniform external magnetic fields by employing the concurrence as entanglement measure.It is found that both the intrinsic decoherence and the anisotropy of the system give a significant suppression to the entanglement.Moreover it finds that the initial state of the system plays an important role in the time evolution of the entanglement,which means that the entanglement of the system is independent of the nonuniformity and uniformity of the magnetic field when the system is in the initial state |ψ(0)>=|00>and |ψ(0)>=m |01＞+n|10＞,respectively.
Characteristic parameters and dynamics of two-qubit system in self-assembled monolayers
Rinkevicius, Z; Tsifrinovich, V I; Tretiak, S; Rinkevicius, Zilvinas; Berman, Gennady P.; Tsifrinovich, Vladimir I.; Tretiak, Sergei
2004-01-01
We suggest the application of nitronylnitroxide substituted with methyl group and 2,2,6,6-tetramethylpiperidin organic radicals as 1/2-spin qubits for self-assembled monolayer quantum devices. We show that the oscillating cantilever driven adiabatic reversals technique can provide the read-out of the spin states. We compute components of the $g$-tensor and dipole-dipole interaction tensor for these radicals. We show that the delocalization of the spin in the radical may significantly influence the dipole-dipole interaction between the spins.
Generating and stabilizing the GHZ state in circuit QED: Joint measurement, Zeno effect and feedback
Feng, Wei; Ding, Xinmei; Xu, Luting; Li, Xin-Qi
2011-01-01
In solid-state circuit QED system, we extend the previous study of generating and stabilizing two-qubit Bell state [Phys. Rev. A 82, 032335 (2010)], to three-qubit GHZ state. In dispersive regime, we employ the homodyne joint readout for multiple qubits to infer the state for further processing, and in particular use it to stabilize the state directly by means of an alternate-flip-interrupted Zeno (AFIZ) scheme. Moreover, the state-of-the-art feedback action based on the filtered current enables not only a deterministic generation of the pre-GHZ state in the initial stage, but also a fast recovery from the environment-caused degradation in the later stabilization process. We show that the proposed scheme can maintain the state with high fidelity if the efficient quantum measurement and rapid single-qubit rotations are available.
Quantum steering without inequalities
Chen, Jing-Ling; Wu, Chunfeng; Su, Hong-Yi; Cabello, Adan; Kwek, L C; Oh, C H
2012-01-01
We show that, for any two-qubit state, quantum steering can be proven without testing the violation of steering inequalities. We show that steerability is proven if Bob's normalized conditional states after Alice's measurements are pure. This method, which may be seen as the quantum steering analog of Greenberger-Horne-Zeilinger-like tests of Bell nonlocality without Bell inequalities, offers advantages with respect to the existing methods for experimentally testing quantum steering.
A quantum entropy source on an InP photonic integrated circuit for random number generation
Abellan, Carlos; Domenech, David; Muñoz, Pascual; Capmany, Jose; Longhi, Stefano; Mitchell, Morgan W; Pruneri, Valerio
2016-01-01
Random number generators are essential to ensure performance in information technologies, including cryptography, stochastic simulations and massive data processing. The quality of random numbers ultimately determines the security and privacy that can be achieved, while the speed at which they can be generated poses limits to the utilisation of the available resources. In this work we propose and demonstrate a quantum entropy source for random number generation on an indium phosphide photonic integrated circuit made possible by a new design using two-laser interference and heterodyne detection. The resulting device offers high-speed operation with unprecedented security guarantees and reduced form factor. It is also compatible with complementary metal-oxide semiconductor technology, opening the path to its integration in computation and communication electronic cards, which is particularly relevant for the intensive migration of information processing and storage tasks from local premises to cloud data centre...
Autonomous quantum refrigerator in a circuit QED architecture based on a Josephson junction
Hofer, Patrick P.; Perarnau-Llobet, Martí; Brask, Jonatan Bohr; Silva, Ralph; Huber, Marcus; Brunner, Nicolas
2016-12-01
An implementation of a small quantum absorption refrigerator in a circuit QED architecture is proposed. The setup consists of three harmonic oscillators coupled to a Josephson junction. The refrigerator is autonomous in the sense that it does not require any external control for cooling, but only thermal contact between the oscillators and heat baths at different temperatures. In addition, the setup features a built-in switch, which allows the cooling to be turned on and off. If timing control is available, this enables the possibility for coherence-enhanced cooling. Finally, we show that significant cooling can be achieved with experimentally realistic parameters and that our setup should be within reach of current technology.
Sarabi, B; Ramanayaka, A N; Burin, A L; Wellstood, F C; Osborn, K D
2016-04-22
Material-based two-level systems (TLSs), appearing as defects in low-temperature devices including superconducting qubits and photon detectors, are difficult to characterize. In this study we apply a uniform dc electric field across a film to tune the energies of TLSs within. The film is embedded in a superconducting resonator such that it forms a circuit quantum electrodynamical system. The energy of individual TLSs is observed as a function of the known tuning field. By studying TLSs for which we can determine the tunneling energy, the actual p_{z}, dipole moments projected along the uniform field direction, are individually obtained. A distribution is created with 60 p_{z}. We describe the distribution using a model with two dipole moment magnitudes, and a fit yields the corresponding values p=p_{1}=2.8±0.2 D and p=p_{2}=8.3±0.4 D. For a strong-coupled TLS the vacuum-Rabi splitting can be obtained with p_{z} and tunneling energy. This allows a measurement of the circuit's zero-point electric-field fluctuations, in a method that does not need the electric-field volume.
Sabegh, Z Amini; Maleki, M A; Mahmoudi, M
2015-01-01
We study the propagation and amplification of a microwave field in a four-level cascade quantum system which is realized in a superconducting phase quantum circuit. It is shown that by increasing the microwave pump tones feeding the system, the normal dispersion switches to the anomalous and the gain-assisted superluminal microwave propagation is obtained in this system. Moreover, it is demonstrated that the stimulated microwave field is generated via four-wave mixing without any inversion population in the energy levels of the system (amplification without inversion) and the group velocity of the generated pulse can be controlled by the external oscillating magnetic fluxes. We also show that in some special set of parameters, the absorption-free superluminal generated microwave propagation is obtained in superconducting phase quantum circuit system.
InGaN/GaN multiple quantum well solar cells with an enhanced open-circuit voltage
Institute of Scientific and Technical Information of China (English)
Zhang Xiao-Bin; Wang Xiao-Liang; Xiao Hong-Ling; Yang Cui-Bai; Hou Qi-Feng; Yin Hai-Bo; Chen Hong; Wang Zhan-Guo
2011-01-01
In this paper, InGaN/GaN multiple quantum well solar cells (MQWSCs) with an In content of 0.15 are fabricated and studied. The short-circuit density, fill factor and open-circuit voltage (Voc) of the device are 0.7 mA/cm2, 0.40 and 2.22 V, respectively. The results exhibit a significant enhancement of Voc compared with those of InGaN-based hetero and homojunction cells. This enhancement indicates that the InGaN/GaN MQWSC offers an effective way for increasing Voc of an In-rich InxGa1-xN solar cell. The device exhibits an external quantum efficiency (EQE) of 36% (7%) at 388 nm (430 nm). The photovoltaic performance of the device can be improved by optimizing the structure of the InGaN/GaN multiple quantum well.
Realizing and characterizing chiral photon flow in a circuit quantum electrodynamics necklace
Wang, Yan-Pu; Wang, Wei; Xue, Zheng-Yuan; Yang, Wan-Li; Hu, Yong; Wu, Ying
2015-02-01
Gauge theory plays the central role in modern physics. Here we propose a scheme of implementing artificial Abelian gauge fields via the parametric conversion method in a necklace of superconducting transmission line resonators (TLRs) coupled by superconducting quantum interference devices (SQUIDs). The motivation is to synthesize an extremely strong effective magnetic field for charge-neutral bosons which can hardly be achieved in conventional solid-state systems. The dynamic modulations of the SQUIDs can induce effective magnetic fields for the microwave photons in the TLR necklace through the generation of the nontrivial hopping phases of the photon hopping between neighboring TLRs. To demonstrate the synthetic magnetic field, we study the realization and detection of the chiral photon flow dynamics in this architecture under the influence of decoherence. Taking the advantages of its simplicity and flexibility, this parametric scheme is feasible with state-of-the-art technology and may pave an alternative way for investigating the gauge theories with superconducting quantum circuits. We further propose a quantitative measure for the chiral property of the photon flow. Beyond the level of qualitative description, the dependence of the chiral flow on external pumping parameters and cavity decay is characterized.
Realizing and characterizing chiral photon flow in a circuit quantum electrodynamics necklace.
Wang, Yan-Pu; Wang, Wei; Xue, Zheng-Yuan; Yang, Wan-Li; Hu, Yong; Wu, Ying
2015-02-10
Gauge theory plays the central role in modern physics. Here we propose a scheme of implementing artificial Abelian gauge fields via the parametric conversion method in a necklace of superconducting transmission line resonators (TLRs) coupled by superconducting quantum interference devices (SQUIDs). The motivation is to synthesize an extremely strong effective magnetic field for charge-neutral bosons which can hardly be achieved in conventional solid-state systems. The dynamic modulations of the SQUIDs can induce effective magnetic fields for the microwave photons in the TLR necklace through the generation of the nontrivial hopping phases of the photon hopping between neighboring TLRs. To demonstrate the synthetic magnetic field, we study the realization and detection of the chiral photon flow dynamics in this architecture under the influence of decoherence. Taking the advantages of its simplicity and flexibility, this parametric scheme is feasible with state-of-the-art technology and may pave an alternative way for investigating the gauge theories with superconducting quantum circuits. We further propose a quantitative measure for the chiral property of the photon flow. Beyond the level of qualitative description, the dependence of the chiral flow on external pumping parameters and cavity decay is characterized.
Indian Academy of Sciences (India)
E K Bashkirov; M S Mastyugin
2015-01-01
Considering two artificial identical atoms interacting with two-mode thermal field through non-degenerate two-photon transitions, this paper studies the influence of atomic coherence and dipole–dipole interaction on the entanglement of two qubits. It is found that the entanglement is greatly enhanced by these mechanisms.
Girdhar, Parth; Cavalcanti, Eric G.
2016-09-01
We derive an inequality that is necessary and sufficient to show Einstein-Podolsky-Rosen (EPR) steering in a scenario employing only correlations between two arbitrary dichotomic measurements on each party. Thus the inequality is a complete steering analogy of the Clauser-Horne-Shimony-Holt (CHSH) inequality, a generalization of the result of Cavalcanti et al. [E. G. Cavalcanti, C. J. Foster, M. Fuwa, and H. M. Wiseman, JOSA B 32, A74 (2015), 10.1364/JOSAB.32.000A74]. We show that violation of the inequality only requires measuring over equivalence classes of mutually unbiased measurements on the trusted party and that in fact assuming a general two-qubit system arbitrary pairs of distinct projective measurements at the trusted party are equally useful. Via this it is found that for a given state the maximum violation of our EPR-steering inequality is equal to that for the CHSH inequality, so all states that are EPR steerable with CHSH-type correlations are also Bell nonlocal.
Slater, Paul B
2010-01-01
We study the moments of probability distributions generated by certain determinantal functions of generic two-qubit density matrices (rho) with real entries over the associated nine-dimensional convex domain, assigned Hilbert-Schmidt measure. It is found that the mean of the (nonnegative) determinant |rho| is 1/2288, the mean of the determinant of the partial transpose |rho^{PT}|--negative values indicating entanglement--is -1/858, while the mean of the product of these two determinants is zero. We ascertain the exact values--also rational numbers--of the succeeding eight moments of |rho^{PT}|. At intermediate steps in the derivation of the m-th moment, rational functions C_{2 j}(m) emerge, yielding the coefficients of the 2j-th power of even polynomials of total degree 4 m. These functions possess poles at finite series of consecutive half-integers, and certain (trivial) roots at finite series of consecutive natural numbers. The (nontrivial) dominant roots of C_{2 j}(m) appear to converge to the same half-in...
Quantum computation architecture using optical tweezers
DEFF Research Database (Denmark)
Weitenberg, Christof; Kuhr, Stefan; Mølmer, Klaus;
2011-01-01
We present a complete architecture for scalable quantum computation with ultracold atoms in optical lattices using optical tweezers focused to the size of a lattice spacing. We discuss three different two-qubit gates based on local collisional interactions. The gates between arbitrary qubits...... quantum computing....
Nanofabrication for On-Chip Optical Levitation, Atom-Trapping, and Superconducting Quantum Circuits
Norte, Richard Alexander
a final value of Qm = 5.8(1.1) x 105, representing more than an order of magnitude improvement over the conventional limits of SiO2 for a pendulum geometry. Our technique may enable new opportunities for mechanical sensing and facilitate observations of quantum behavior in this class of mechanical systems. We then give a detailed overview of the techniques used to produce high-aspect-ratio nanostructures with applications in a wide range of quantum optics experiments. The ability to fabricate such nanodevices with high precision opens the door to a vast array of experiments which integrate macroscopic optical setups with lithographically engineered nanodevices. Coupled with atom-trapping experiments in the Kimble Lab, we use these techniques to realize a new waveguide chip designed to address ultra-cold atoms along lithographically patterned nanobeams which have large atom-photon coupling and near 4pi Steradian optical access for cooling and trapping atoms. We describe a fully integrated and scalable design where cold atoms are spatially overlapped with the nanostring cavities in order to observe a resonant optical depth of d0 ≈ 0.15. The nanodevice illuminates new possibilities for integrating atoms into photonic circuits and engineering quantum states of atoms and light on a microscopic scale. We then describe our work with superconducting microwave resonators coupled to a phononic cavity towards the goal of building an integrated device for quantum-limited microwave-to-optical wavelength conversion. We give an overview of our characterizations of several types of substrates for fabricating a low-loss high-frequency electromechanical system. We describe our electromechanical system fabricated on a SiN membrane which consists of a 12 GHz superconducting LC resonator coupled capacitively to the high frequency localized modes of a phononic nanobeam. Using our suspended membrane geometry we isolate our system from substrates with significant loss tangents
Petrov, A. A.; Davydov, V. V.
2016-03-01
In this work the study, design, development and experimental results of a new microwave excitation signal generating circuit are presented. New design of this circuit is based on the method of direct digital synthesis. The results of theoretical calculations and experimental researches show that the new design not only has a high precision, but also has an improvement in the spectral characteristics of the output signal. Range of generated output frequencies is expanded, that leads to the possibility of detuning the frequency of the neighboring resonance of spectral line and adjust the C-field in quantum frequency standard. Experimental research of the metrological characteristics of the quantum frequency standard on the atoms of caesium with a new functional unit showed an improvement in the daily frequency stability.
Nataf, Pierre; Ciuti, Cristiano
2010-09-07
In cavity quantum electrodynamics (QED), the interaction between an atomic transition and the cavity field is measured by the vacuum Rabi frequency Ω(0). The analogous term 'circuit QED' has been introduced for Josephson junctions, because superconducting circuits behave as artificial atoms coupled to the bosonic field of a resonator. In the regime with Ω(0) comparable with the two-level transition frequency, 'superradiant' quantum phase transitions for the cavity vacuum have been predicted, for example, within the Dicke model. In this study, we prove that if the time-independent light-matter Hamiltonian is considered, a superradiant quantum critical point is forbidden for electric dipole atomic transitions because of the oscillator strength sum rule. In circuit QED, the analogous of the electric dipole coupling is the capacitive coupling, and such no-go property can be circumvented by Cooper pair boxes capacitively coupled to a resonator, because of their peculiar Hilbert space topology and a violation of the corresponding sum rule.
Chancellor, N.; Zohren, S.; Warburton, P. A.
2017-06-01
Quantum annealing provides a way of solving optimization problems by encoding them as Ising spin models which are implemented using physical qubits. The solution of the optimization problem then corresponds to the ground state of the system. Quantum tunneling is harnessed to enable the system to move to the ground state in a potentially high non-convex energy landscape. A major difficulty in encoding optimization problems in physical quantum annealing devices is the fact that many real world optimization problems require interactions of higher connectivity, as well as multi-body terms beyond the limitations of the physical hardware. In this work we address the question of how to implement multi-body interactions using hardware which natively only provides two-body interactions. The main result is an efficient circuit design of such multi-body terms using superconducting flux qubits in which effective N-body interactions are implemented using N ancilla qubits and only two inductive couplers. It is then shown how this circuit can be used as the unit cell of a scalable architecture by applying it to a recently proposed embedding technique for constructing an architecture of logical qubits with arbitrary connectivity using physical qubits which have nearest-neighbor four-body interactions. It is further shown that this design is robust to non-linear effects in the coupling loops, as well as mismatches in some of the circuit parameters.
Nonlocal quantum cloning via quantum dots trapped in distant cavities
Institute of Scientific and Technical Information of China (English)
Yu Tao; Zhu Ai-Dong; Zhang Shou
2012-01-01
A scheme for implementing nonlocal quantum cloning via quantum dots trapped in cavities is proposed.By modulating the parameters of the system,the optimal 1 → 2 universal quantum cloning machine,1 → 2 phase-covariant cloning machine,and 1 → 3 economical phase-covariant cloning machine are constructed.The present scheme,which is attainable with current technology,saves two qubits compared with previous cloning machines.
Memory cost of quantum contextuality
Kleinmann, Matthias; Portillo, José R; Larsson, Jan-Åke; Cabello, Adán
2010-01-01
The simulation of quantum effects requires certain classical resources, and quantifying them is an important step in order to understand the difference between quantum and classical physics. We investigate the minimum classical memory needed to simulate the phenomenon of state-independent quantum contextuality in sequential measurements. We derive optimal simulation strategies for several important cases and prove that two bits of classical memory do not suffice to reproduce the results of sequential measurements on a two-qubit system.
Institute of Scientific and Technical Information of China (English)
Wu Yu-Lin; Deng Hui; Yu Hai-Feng; Xue Guang-Ming; Tian Ye; Li Jie; Chen Ying-Fei
2013-01-01
Besides serving as promising candidates for realizing quantum computing,superconducting quantum circuits are one of a few macroscopic physical systems in which fundamental quantum phenomena can be directly demonstrated and tested,giving rise to a vast field of intensive research work both theoretically and experimentally.In this paper we report our work on the fabrication of superconducting quantum circuits,starting from its building blocks:Al/AlOx/Al Josephson junctions.By using electron beam lithography patterning and shadow evaporation,we have fabricated aluminum Josephson junctions with a controllable critical current density (jc) and wide range of junction sizes from 0.01 μm2 up to 1 μm2.We have carried out systematical studies on the oxidation process in fabricating Al/AlOx/Al Josephson junctions suitable for superconducting flux qubits.Furthermore,we have also fabricated superconducting quantum circuits such as superconducting flux qubits and charge-flux qubits.
Zhang, L.X.; Leburton, J.P.; Hanson, R.; Kouwenhoven, L.P.
2004-01-01
We show that the design of a quantum point contact adjacent to a quantum dot can be optimized to produce maximum sensitivity to single-electron charging in the quantum dot. Our analysis is based on the self-consistent solution of coupled three-dimensional Kohn-Sham and Poisson equations for the
Wang, Xihua
2011-10-26
Colloidal quantum dots (CQDs) enable multijunction solar cells using a single material programmed using the quantum size effect. Here we report the systematic engineering of 1.6 eV PbS CQD solar cells, optimal as the front cell responsible for visible-wavelength harvesting in tandem photovoltaics. We rationally optimize each of the device\\'s collecting electrodes-the heterointerface with electron-accepting TiO2 and the deep-work-function hole-collecting MoO3 for ohmic contact-for maximum efficiency. We report an open-circuit voltage of 0.70 V, the highest observed in a colloidal quantum dot solar cell operating at room temperature. We report an AM1.5 solar power conversion efficiency of 3.5%, the highest observed in >1.5 eV bandgap CQD PV device. © 2011 American Chemical Society.
Luxmoore, I J; Wasley, N A; Ramsay, A J; Thijssen, A C T; Oulton, R; Hugues, M; Kasture, S; Achanta, V G; Fox, A M; Skolnick, M S
2013-01-18
An in-plane spin-photon interface is essential for the integration of quantum dot spins with optical circuits. The optical dipole of a quantum dot lies in the plane and the spin is optically accessed via circularly polarized selection rules. Hence, a single waveguide, which can transport only one in-plane linear polarization component, cannot communicate the spin state between two points on a chip. To overcome this issue, we introduce a spin-photon interface based on two orthogonal waveguides, where the polarization emitted by a quantum dot is mapped to a path-encoded photon. We demonstrate operation by deducing the spin using the interference of in-plane photons. A second device directly maps right and left circular polarizations to antiparallel waveguides, surprising for a nonchiral structure but consistent with an off-center dot.
Eichler, C.; Mlynek, J.; Butscher, J.; Kurpiers, P.; Hammerer, K.; Osborne, T. J.; Wallraff, A.
2015-10-01
Improving the understanding of strongly correlated quantum many-body systems such as gases of interacting atoms or electrons is one of the most important challenges in modern condensed matter physics, materials research, and chemistry. Enormous progress has been made in the past decades in developing both classical and quantum approaches to calculate, simulate, and experimentally probe the properties of such systems. In this work, we use a combination of classical and quantum methods to experimentally explore the properties of an interacting quantum gas by creating experimental realizations of continuous matrix product states—a class of states that has proven extremely powerful as a variational ansatz for numerical simulations. By systematically preparing and probing these states using a circuit quantum electrodynamics system, we experimentally determine a good approximation to the ground-state wave function of the Lieb-Liniger Hamiltonian, which describes an interacting Bose gas in one dimension. Since the simulated Hamiltonian is encoded in the measurement observable rather than the controlled quantum system, this approach has the potential to apply to a variety of models including those involving multicomponent interacting fields. Our findings also hint at the possibility of experimentally exploring general properties of matrix product states and entanglement theory. The scheme presented here is applicable to a broad range of systems exploiting strong and tunable light-matter interactions.
On the quantum information processing in nuclear magnetic resonance quantum computing experiments
Energy Technology Data Exchange (ETDEWEB)
Azevedo, E.R. de; Bonk, F.A.; Vidoto, E.L.G.; Bonagamba, T.J. [Universidade de Sao Paulo (IFSC/USP), Sao Carlos, SP (Brazil). Inst. de Fisica; Sarthour, R.S.; Guimaraes, A.P.; Oliveira, I.S. [Centro Brasileiro de Pesquisas Fisicas (CBPF), Rio de Janeiro, RJ (Brazil); Freitas, J.C.C. [Universidade Federal do Espirito Santo (UFES), Vitoria, ES (Brazil). Dept. de Fisica
2003-07-01
Full text: Nuclear Magnetic Resonance appeared in the late nineties to be the most promising candidate to run quantum computing algorithms. An impressive number of experiments demonstrating the implementation of all logic gates and quantum algorithms in systems with a small number of qubits stimulated the general excitement about the technique, and greatly promoted the field. Particularly important were those experiments where entanglement of particles were aimed at. Entanglement is the most fundamental (and weird !) aspect of quantum systems, and is at the basis of quantum teleportation and quantum cryptography, yet impossible to prove in NMR experiments. The hardcore of NMR quantum computing are the so-called pseudo-pure states, upon which radiofrequency (RF) pulses act to implement quantum mechanical unitary transformations, promoting changes in both, Zeeman level populations and coherences in the density matrix. Whereas pseudo-pure states are special non-equilibrium diagonal states, coherences encode information about superposition states. Now, one could safely say that the whole business of quantum computing goes about controlling relative ket phases. In spite of the impossibility to univocally associating a given quantum state to a NMR spectrum, it is possible to demonstrate the phase action of RF pulses over relative ket phases, even if no population changes take place. In this talk these issues will be addressed, and we will show experimental results of our own where this is done in the two-qubit quadrupole nuclei {sup 23}Na in C{sub 10}H{sub 21}NaO{sub 4}S liquid crystal. We demonstrate the reversibility of the Hadamard gate, and of a quantum circuit which generates pseudo-Bell states. The success of the operation reaches almost 100% in the case of the state |01+|10, 80% in the cases of |00> + |01> and |10> + |11>, and 65% for the cat-state |00> + |11>. (author)
Pairwise Quantum Correlations for Superpositions of Dicke States
Institute of Scientific and Technical Information of China (English)
席政军; 熊恒娜; 李永明; 王晓光
2012-01-01
Pairwise correlation is really an important property for multi-qubit states.For the two-qubit X states extracted from Dicke states and their superposition states,we obtain a compact expression of the quantum discord by numerical check.We then apply the expression to discuss the quantum correlation of the reduced two-qubit states of Dicke states and their superpositions,and the results are compared with those obtained by entanglement of formation,which is a quantum entanglement measure.
Energy Technology Data Exchange (ETDEWEB)
Maunz, Peter Lukas Wilhelm [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Sterk, Jonathan David [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Lobser, Daniel [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Parekh, Ojas D. [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States); Ryan-Anderson, Ciaran [Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
2016-01-01
In recent years, advanced network analytics have become increasingly important to na- tional security with applications ranging from cyber security to detection and disruption of ter- rorist networks. While classical computing solutions have received considerable investment, the development of quantum algorithms to address problems, such as data mining of attributed relational graphs, is a largely unexplored space. Recent theoretical work has shown that quan- tum algorithms for graph analysis can be more efficient than their classical counterparts. Here, we have implemented a trapped-ion-based two-qubit quantum information proces- sor to address these goals. Building on Sandia's microfabricated silicon surface ion traps, we have designed, realized and characterized a quantum information processor using the hyperfine qubits encoded in two 171 Yb + ions. We have implemented single qubit gates using resonant microwave radiation and have employed Gate set tomography (GST) to characterize the quan- tum process. For the first time, we were able to prove that the quantum process surpasses the fault tolerance thresholds of some quantum codes by demonstrating a diamond norm distance of less than 1 . 9 x 10 [?] 4 . We used Raman transitions in order to manipulate the trapped ions' motion and realize two-qubit gates. We characterized the implemented motion sensitive and insensitive single qubit processes and achieved a maximal process infidelity of 6 . 5 x 10 [?] 5 . We implemented the two-qubit gate proposed by Molmer and Sorensen and achieved a fidelity of more than 97 . 7%.
Directory of Open Access Journals (Sweden)
Kristopher Chandía Valenzuela
2006-08-01
Full Text Available ABSTRACT As it is known, quantum inductive circuits with charge discreteness show Bloch-like oscillations in electrical current under a dc external voltage. In this paper, the effect of a superimposed ac voltage in the circuit is considered. The Shapiro effect is found to be related to the existence of resonance. Surprisingly, in the limit of low frequency (no resonance, the electrical averaged current exists and has always the same sign. Eventually this allows for an experimental method to measure discrete charge effect in quantum mesoscopic circuits.RESUMEN Es sabido que circuitos cuánticos inductivos con carga discreta, cuando se someten a un voltaje continuo externo, presentan oscilaciones de Bloch en la corriente. En este trabajo se considera, además, la superposición de un voltaje alterno en el circuito. El efecto Shapiro, relacionado con la existencia de resonancias, es encontrado de modo explícito. Sorprendentemente, en el límite de bajas frecuencias (sin resonancia la corriente eléctrica promediada existe y tiene siempre el mismo signo. Eventualmente, esto entrega un método experimental para medir los efectos de la discretización de la carga en circuitos cuánticos mesosocópicos.
Nori, Franco
2008-03-01
Superconducting (SC) circuits can behave like atoms making transitions between a few energy levels. Such circuits can test quantum mechanics at macroscopic scales and be used to conduct atomic-physics experiments on a silicon chip. This talk overviews a few of our theoretical studies on SC circuits and quantum information processing (QIP) including: SC qubits for single photon generation and for lasing; controllable couplings among qubits; how to increase the coherence time of qubits using a capacitor in parallel to one of the qubit junctions; hybrid circuits involving both charge and flux qubits; testing Bell's inequality in SC circuits; generation of GHZ states; quantum tomography in SC circuits; preparation of macroscopic quantum superposition states of a cavity field via coupling to a SC qubit; generation of nonclassical photon states using a SC qubit in a microcavity; scalable quantum computing with SC qubits; and information processing with SC qubits in a microwave field. Controllable couplings between qubits can be achieved either directly or indirectly. This can be done with and without coupler circuits, and with and without data-buses like EM fields in cavities (e.g., we will describe both the variable-frequency magnetic flux approach and also a generalized double-resonance approach that we introduced). It is also possible to ``turn a quantum bug into a feature'' by using microscopic defects as qubits, and the macroscopic junction as a controller of it. We have also studied ways to implement radically different approaches to QIP by using ``cluster states'' in SC circuits. For a general overview of this field, see, J.Q. You and F. Nori, Phys. Today 58 (11), 42 (2005)
DEFF Research Database (Denmark)
Ding, Yunhong; Bacco, Davide; Dalgaard, Kjeld
2017-01-01
Quantum key distribution provides an efficient means to exchange information in an unconditionally secure way. Historically, quantum key distribution protocols have been based on binary signal formats, such as two polarization states, and the transmitted information efficiency of the quantum key...
Yoshihara, F.; Fuse, T.; Ashhab, S.; Kakuyanagi, K.; Saito, S.; Semba, K.
2017-05-01
We report on spectra of circuit-quantum-electrodynamics (QED) systems in an intermediate regime that lies between the ultrastrong- and the deep-strong-coupling regimes, which have been reported previously in the literature. Our experimental results, along with numerical simulations, demonstrate that as the coupling strength increases, the spectrum of a circuit-QED system undergoes multiple qualitative transformations, such that several coupling regimes are identified, each with its own unique spectral features. The different spectral transformations can be related to crossings between energy level differences and to changes in the symmetries of the energy eigenstates. These results allow us to use qualitative spectral features to infer certain properties and parameters of the system.
A study of Quantum Correlations in Open Quantum Systems
Chakrabarty, Indranil; Siddharth, Nana
2010-01-01
In this work, we study quantum correlations in mixed states. The states studied are modelled by a two-qubit system interacting with its environment via a quantum nondemolition (purely dephasing) as well as dissipative type of interaction. The entanglement dynamics of this two qubit system is analyzed and the existence of entangled states which do not violate Bell's inequality, but can still be useful as a potential resource for teleportation are reported. In addition, a comparative study of various measures of quantum correlations, like Concurrence, Bell's inequality, Discord and Teleportation fidelity, is made on these states, generated by the above evolutions. Interestingly, examples are found, of states, where entanglement is vanishing, but discord is non-vanishing, bringing out the fact that entanglement is a subset of quantum correlations.
Cavity quantum networks for quantum information processing in decoherence-free subspace
Institute of Scientific and Technical Information of China (English)
Hua WEI; Zhi-jiao DENG; Wan-li YANG; Fei ZHOU
2009-01-01
We give a brief review on the quantum infor- mation processing in decoherence-free subspace (DFS). We show how to realize the initialization of the entangled quantum states, information transfer and teleportation of quantum states, two-qubit Grover search and how to construct the quantum network in DFS, within the cav- ity QED regime based on a cavity-assisted interaction by single-photon pulses.
Energy Technology Data Exchange (ETDEWEB)
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.
Directory of Open Access Journals (Sweden)
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.
Quantum Discrete Fourier Transform in an Ion Trap System
Institute of Scientific and Technical Information of China (English)
ZHENG Shi-Biao
2007-01-01
We propose two schemes for the implementation of quantum discrete Fourier transform in the ion trap system. In each scheme we design a tunable two-qubit phase gate as the main ingredient. The experimental implementation of the schemes would be an important step toward complex quantum computation in the ion trap system.
Stability of Mixed Nash Equilibria in Symmetric Quantum Games
Institute of Scientific and Technical Information of China (English)
A.Iqbal; A.H.Toor
2004-01-01
In bimatrix games the Bishop-Cannings theorem of the classical evolutionary game theory does not permit pure evolutionarily stable strategies (ESSs) when a mixed ESS exists. We find the necessary form of two-qubit initial quantum states when a switch-over to a quantum version of the game also changes the evolutionary stability of a mixed symmetric Nash equilibrium.
Quantum entanglement and quantum computational algorithms
Indian Academy of Sciences (India)
Arvind
2001-02-01
The existence of entangled quantum states gives extra power to quantum computers over their classical counterparts. Quantum entanglement shows up qualitatively at the level of two qubits. We demonstrate that the one- and the two-bit Deutsch-Jozsa algorithm does not require entanglement and can be mapped onto a classical optical scheme. It is only for three and more input bits that the DJ algorithm requires the implementation of entangling transformations and in these cases it is impossible to implement this algorithm classically
Goudarzi, H.; Dousti, M. J.; Shafaei, A.; Pedram, M.
2014-05-01
This paper presents a physical mapping tool for quantum circuits, which generates the optimal universal logic block (ULB) that can, on average, perform any logical fault-tolerant (FT) quantum operations with the minimum latency. The operation scheduling, placement, and qubit routing problems tackled by the quantum physical mapper are highly dependent on one another. More precisely, the scheduling solution affects the quality of the achievable placement solution due to resource pressures that may be created as a result of operation scheduling, whereas the operation placement and qubit routing solutions influence the scheduling solution due to resulting distances between predecessor and current operations, which in turn determines routing latencies. The proposed flow for the quantum physical mapper captures these dependencies by applying (1) a loose scheduling step, which transforms an initial quantum data flow graph into one that explicitly captures the no-cloning theorem of the quantum computing and then performs instruction scheduling based on a modified force-directed scheduling approach to minimize the resource contention and quantum circuit latency, (2) a placement step, which uses timing-driven instruction placement to minimize the approximate routing latencies while making iterative calls to the aforesaid force-directed scheduler to correct scheduling levels of quantum operations as needed, and (3) a routing step that finds dynamic values of routing latencies for the qubits. In addition to the quantum physical mapper, an approach is presented to determine the single best ULB size for a target quantum circuit by examining the latency of different FT quantum operations mapped onto different ULB sizes and using information about the occurrence frequency of operations on critical paths of the target quantum algorithm to weigh these latencies. Experimental results show an average latency reduction of about 40 % compared to previous work.
Giant photon gain in large-scale quantum dot circuit-QED systems
Agarwalla, Bijay Kumar; Mukamel, Shaul; Segal, Dvira
2016-01-01
Motivated by recent experiments on the generation of coherent light in engineered hybrid quantum systems, we investigate gain in a microwave photonic cavity coupled to quantum dot structures, and develop concrete directions for achieving a giant amplification in photon transmission. We propose two architectures for scaling up the electronic gain medium: (i) $N$ double quantum dot systems (N-DQD), (ii) $M$ quantum dots arranged in series akin to a quantum cascade laser setup. In both setups, the fermionic reservoirs are voltage biased, and the quantum dots are coupled to a single-mode cavity. Optical amplification is explained based on a sum rule for the transmission function, and it is determined by an intricate competition between two different processes: charge density response in the gain medium, and cavity losses to input and output ports. The same design principle is also responsible for the corresponding giant amplification in other photonic observables, mean photon number and emission spectrum, thereby...
Quantum transitions and quantum entanglement from Dirac-like dynamics simulated by trapped ions
Bittencourt, Victor A. S. V.; Bernardini, Alex E.; Blasone, Massimo
2016-05-01
Quantum transition probabilities and quantum entanglement for two-qubit states of a four-level trapped ion quantum system are computed for time-evolving ionic states driven by Jaynes-Cummings Hamiltonians with interactions mapped onto a SU(2 )⊗SU(2 ) group structure. Using the correspondence of the method of simulating a 3 +1 dimensional Dirac-like Hamiltonian for bispinor particles into a single trapped ion, one preliminarily obtains the analytical tools for describing ionic state transition probabilities as a typical quantum oscillation feature. For Dirac-like structures driven by generalized Poincaré classes of coupling potentials, one also identifies the SU(2 )⊗SU(2 ) internal degrees of freedom corresponding to intrinsic parity and spin polarization as an adaptive platform for computing the quantum entanglement between the internal quantum subsystems which define two-qubit ionic states. The obtained quantum correlational content is then translated into the quantum entanglement of two-qubit ionic states with quantum numbers related to the total angular momentum and to its projection onto the direction of the trapping magnetic field. Experimentally, the controllable parameters simulated by ion traps can be mapped into a Dirac-like system in the presence of an electrostatic field which, in this case, is associated to ionic carrier interactions. Besides exhibiting a complete analytical profile for ionic quantum transitions and quantum entanglement, our results indicate that carrier interactions actively drive an overall suppression of the quantum entanglement.
Wang, Hao-Tian; Zou, Yang; Ge, Rong-Chun; Guo, Guang-Can
2010-01-01
We present a detailed study of the entanglement dynamics of a two-qubit system coupled to independent non-Markovian environments, employing hierarchy equations. This recently developed theoretical treatment can conveniently solve non-Markovian problems and take into consideration the correlation between the system and bath in an initial state. We concentrate on calculating the death and rebirth time points of the entanglement to obtain a general view of the concurrence curve and explore the behavior of entanglement dynamics with respect to the coupling strength, the characteristic frequency of the noise bath and the environment temperature.
Institute of Scientific and Technical Information of China (English)
LIANG XIAN-TING; FAN HONG-YI
2001-01-01
By using the charge and current in a quantization resistance-inductance-capacitance (RLC) electric circuit, we construct a pair of canonical variables. Using this pair of variables and the thermal field dynamics, we obtain the fluctuations of charge and current in the RLC electric circuit at finite temperatures. It is shown that the fluctuations increase with increasing temperature and decrease with prolonging of time.
High-Speed Large-Alphabet Quantum Key Distribution Using Photonic Integrated Circuits
2014-01-28
Lett., 93:010503, Jul 2004. [14] Irfan Ali-Khan, Curtis J. Broadbent , and John C. Howell. Large-Alphabet Quantum Key Distribution Using Energy-Time...Rev. Lett., 92:167903, Apr 2004. [20] Irfan Ali-Khan, Curtis J. Broadbent , and John C. Howell. Large-Alphabet Quantum Key Distribution Using Energy
Controlled quantum state transfer via parity measurement
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
In this work,a scheme for controlled quantum state transfer is proposed using parity measurement in a cavity-waveguide system.As two special cases,two schemes of controlled quantum state transfer for one qubit and two qubits are investigated in detail.An important advantage is that controlled quantum state transfer can be completed by single-qubit rotations and the measurement of parity.Therefore,the present scheme might be realized in the scope of current experimental technology.
Controlled quantum state transfer via parity measurement
Institute of Scientific and Technical Information of China (English)
YUAN Quan; LI JiuHui
2009-01-01
In this work, a scheme for controlled quantum state transfer is proposed using parity measurement in a cavity-waveguide system. As two special cases, two schemes of controlled quantum state transfer for one qubit and two qubits are investigated in detail. An important advantage is that controlled quantum state transfer can be completed by single-qubit rotations and the measurement of parity. Therefore, the present scheme might be realized in the scope of current experimental technology.
Hwang, Myung-Joong; Kim, M S; Choi, Mahn-Soo
2016-04-15
We explore the photon population dynamics in two coupled circuit QED systems. For a sufficiently weak intercavity photon hopping, as the photon-cavity coupling increases, the dynamics undergoes double transitions first from a delocalized to a localized phase and then from the localized to another delocalized phase. The latter delocalized phase is distinguished from the former one; instead of oscillating between the two cavities, the photons rapidly quasiequilibrate over the two cavities. These intriguing features are attributed to an interplay between two qualitatively distinctive nonlinear behaviors of the circuit QED systems in the utrastrong coupling regime, whose distinction has been widely overlooked.
Engineering Dissipation to Generate Entanglement Between Remote Superconducting Quantum Bits
Schwartz, Mollie Elisheva
Superconducting quantum circuits provide a promising avenue for scalable quantum computation and simulation. Their chief advantage is that, unlike physical atoms or electrons, these ''artificial atoms'' can be designed with nearly-arbitrarily large coupling to one another and to their electromagnetic environment. This strong coupling allows for fast quantum bit (qubit) operations, and for efficient readout. However, strong coupling comes at a price: a qubit that is strongly coupled to its environment is also strongly susceptible to losses and dissipation, as coherent information leaks from the quantum system under study into inaccessible ''bath'' modes. Extensive work in the field is dedicated to engineering away these losses to the extent possible, and to using error correction to undo the effects of losses that are unavoidable. This dissertation explores an alternate approach to dissipation: we study avenues by which dissipation itself can be used to generate, rather than destroy, quantum resources. We do so specifically in the context of quantum entanglement, one of the most important and most counter-intuitive aspects of quantum mechanics. Entanglement generation and stabilization is critical to most non-trivial implementations of quantum computing and quantum simulation, as it is the property that distinguishes a multi-qubit quantum system from a string of classical bits. The ability to harness dissipation to generate, purify, and stabilize entanglement is therefore highly desirable. We begin with an overview of quantum dissipation and measurement, followed by an introduction to entanglement and to the superconducting quantum information architecture. We then discuss three sets of experiments that highlight and explore the powerful uses of dissipation in quantum systems. First, we use an entangling measurement to probabilistically generate entanglement between two qubits separated by more than one meter of ordinary cable. This represents the first achievement
Quantum Computer Using Coupled Quantum Dot Molecules
Wu, N J; Natori, A; Yasunaga, H; Wu*, Nan-Jian
1999-01-01
We propose a method for implementation of a quantum computer using artificial molecules. The artificial molecule consists of two coupled quantum dots stacked along z direction and one single electron. One-qubit and two-qubit gates are constructed by one molecule and two coupled molecules, respectively.The ground state and the first excited state of the molecule are used to encode the |0> and |1> states of a qubit. The qubit is manipulated by a resonant electromagnetic wave that is applied directly to the qubit through a microstrip line. The coupling between two qubits in a quantum controlled NOT gate is switched on (off) by floating (grounding) the metal film electrodes. We study the operations of the gates by using a box-shaped quantum dot model and numerically solving a time-dependent Schridinger equation, and demonstrate that the quantum gates can perform the quantum computation. The operating speed of the gates is about one operation per 4ps. The reading operation of the output of the quantum computer can...
Directory of Open Access Journals (Sweden)
Andre Vatarescu
2016-11-01
Full Text Available An approximation-free and fully quantum optic formalism for parametric processes is presented. Phase-dependent gain coefficients and related phase-pulling effects are identified for quantum Rayleigh emission and the electro-optic conversion of photons providing parametric amplification in small-scale integration of photonic devices. These mechanisms can be manipulated to deliver, simultaneously, sub-Poissonian distributions of photons as well as phase-dependent amplification in the same optical quadrature of a signal field.
Lari, Behzad
2011-01-01
This is a thesis submitted to university of Pune, India, for the Ph.D. degree. This work deals with entanglement production in two qubit, two qutrit and three qubit systems, entanglement in indistinguishable fermionic systems, quantum discord in a Heisenberg chain and geometric measure of quantum discord in an arbitrary state of a bipartite quantum system.
Controlled phase gates based on two nonidentical quantum dots trapped in separate cavities
Institute of Scientific and Technical Information of China (English)
Wang Xiao-Xia; Zhang Jian-Qi; Yu Ya-Fei; Zhang Zhi-Ming
2011-01-01
We propose a scheme for realizing two-qubit controlled phase gates on two nonidentical quantum dots trapped in separate cavities.In our scheme,each dot simultaneously interacts with one highly detuned cavity mode and two strong driven classical fields.During the gate operation,the quantum dots undergo no transition,while the system can acquire different phases conditional on different states of the quantum dots.With the application of the single-qubit operations,two-qubit controlled phase gates can be realized.
Experimental estimation of entanglement at the quantum limit.
Brida, Giorgio; Degiovanni, Ivo Pietro; Florio, Angela; Genovese, Marco; Giorda, Paolo; Meda, Alice; Paris, Matteo G A; Shurupov, Alexander
2010-03-12
Entanglement is the central resource of quantum information processing and the precise characterization of entangled states is a crucial issue for the development of quantum technologies. This leads to the necessity of a precise, experimental feasible measure of entanglement. Nevertheless, such measurements are limited both from experimental uncertainties and intrinsic quantum bounds. Here we present an experiment where the amount of entanglement of a family of two-qubit mixed photon states is estimated with the ultimate precision allowed by quantum mechanics.
Kasai, S.; Yumoto, M; Sato, T.; Hasegawa, H.
2004-01-01
This paper discusses feasibility of design and future implementation of ultrasmall-size and ultra-low-power digital logic systems by a hexagonal BDD (binary-decision diagram) quantum circuit approach. The discussion is based on various circuits formed on GaAs-based hexagonal nanowire networks controlled by nanometer scale Schottky wrap gates (WPGs). Starting from basic node devices and elementary logic function blocks, fabrication technology of hexagonal BDD quantum circuits up to 8-bit adder...
Castellano, Maria Gabriella; Grönberg, Leif; Carelli, Pasquale; Chiarello, Fabio; Cosmelli, Carlo; Leoni, Roberto; Poletto, Stefano; Torrioli, Guido; Hassel, Juha; Helistö, Panu
2006-08-01
In order to integrate superconducting qubits with rapid-single-flux-quantum (RSFQ) control circuitry, it is necessary to develop a fabrication process that simultaneously fulfils the requirements of both elements: low critical current density, very low operating temperature (tens of millikelvin) and reduced dissipation on the qubit side; high operation frequency, large stability margins, low dissipated power on the RSFQ side. For this purpose, VTT has developed a fabrication process based on Nb trilayer technology, which allows the on-chip integration of superconducting qubits and RSFQ circuits even at very low temperature. Here we present the characterization (at 4.2 K) of the process from the point of view of the Josephson devices and show that they are suitable to build integrated superconducting qubits.
Efficient, High-Speed, Monolithic Optoelectronic Circuits Using Quantum- Confined Structures
1991-07-25
made to optimize the ridge-waveguide laser fabrication process by working on GaAs and In0.2Ga0.sAs single quantum- laser monitoring and polyimidc...with and without a SSL active layer. Because the SSL laser samples are precious, a special effort has been made to optimize the ridge-waveguide laser ... fabrication process by working on GaAs and Ino.2Ga0.sAs single quantum- 20 well SCH structures. It is found that the choice among SiQz, SixNy and
Broadband filters for abatement of spontaneous emission in circuit quantum electrodynamics
Energy Technology Data Exchange (ETDEWEB)
Bronn, Nicholas T., E-mail: ntbronn@us.ibm.com; Hertzberg, Jared B.; Córcoles, Antonio D.; Gambetta, Jay M.; Chow, Jerry M. [IBM T.J. Watson Research Center, 1101 Kitchawan Road, Yorktown Heights, New York 10598 (United States); Liu, Yanbing; Houck, Andrew A. [Department of Electrical Engineering, Princeton University, Princeton, New Jersey 08544 (United States)
2015-10-26
The ability to perform fast, high-fidelity readout of quantum bits (qubits) is essential to the goal of building a quantum computer. However, coupling a fast measurement channel to a superconducting qubit typically also speeds up its relaxation via spontaneous emission. Here, we use impedance engineering to design a filter by which photons may easily leave the resonator at the cavity frequency but not at the qubit frequency. We implement this broadband filter in both an on-chip and off-chip configuration.
Multi-photon dressing of an anharmonic superconducting many-level quantum circuit
Energy Technology Data Exchange (ETDEWEB)
Braumueller, Jochen; Cramer, Joel; Schloer, Steffen; Rotzinger, Hannes; Radtke, Lucas; Lukashenko, Alexander; Yang, Ping; Skacel, Sebastian; Probst, Sebastian; Weides, Martin [Karlsruhe Institute of Technology (KIT), Physikalisches Institut, 76131 Karlsruhe (Germany); Marthaler, Michael; Guo, Lingzhen [Karlsruhe Institute of Technology (KIT), Institut fuer Theoretische Festkoerperphysik, 76131 Karlsruhe (Germany); Ustinov, Alexey V. [Karlsruhe Institute of Technology (KIT), Physikalisches Institut, 76131 Karlsruhe (Germany); National University of Science and Technology MISIS, Moscow 119049 (Russian Federation)
2015-07-01
We report on the investigation of a superconducting anharmonic multi-level circuit that is coupled to a harmonic readout resonator. We observe multi-photon transitions via virtual energy levels of our system up to the fifth excited state. The back-action of these higher-order excitations on our readout device is analyzed quantitatively and demonstrated to be in accordance with theoretical expectation. By applying a strong microwave drive we achieve multi-photon dressing of our system which is dynamically coupled by a weak probe tone. The emerging higher-order Rabi sidebands and associated Autler-Townes splittings involving up to five levels of the investigated anharmonic circuit are observed. Experimental results are in good agreement with master equation simulations.
Takagi, Naofumi; Murakami, Kazuaki; Fujimaki, Akira; Yoshikawa, Nobuyuki; Inoue, Koji; Honda, Hiroaki
We propose a desk-side supercomputer with large-scale reconfigurable data-paths (LSRDPs) using superconducting rapid single-flux-quantum (RSFQ) circuits. It has several sets of computing unit which consists of a general-purpose microprocessor, an LSRDP and a memory. An LSRDP consists of a lot of, e. g., a few thousand, floating-point units (FPUs) and operand routing networks (ORNs) which connect the FPUs. We reconfigure the LSRDP to fit a computation, i. e., a group of floating-point operations, which appears in a ‘for’ loop of numerical programs by setting the route in ORNs before the execution of the loop. We propose to implement the LSRDPs by RSFQ circuits. The processors and the memories can be implemented by semiconductor technology. We expect that a 10 TFLOPS supercomputer, as well as a refrigerating engine, will be housed in a desk-side rack, using a near-future RSFQ process technology, such as 0.35μm process.
Experimental realization of nonadiabatic holonomic quantum computation.
Feng, Guanru; Xu, Guofu; Long, Guilu
2013-05-10
Because of its geometric nature, holonomic quantum computation is fault tolerant against certain types of control errors. Although proposed more than a decade ago, the experimental realization of holonomic quantum computation is still an open challenge. In this Letter, we report the first experimental demonstration of nonadiabatic holonomic quantum computation in a liquid NMR quantum information processor. Two noncommuting one-qubit holonomic gates, rotations about x and z axes, and the two-qubit holonomic CNOT gate are realized by evolving the work qubits and an ancillary qubit nonadiabatically. The successful realizations of these universal elementary gates in nonadiabatic holonomic quantum computation demonstrates the experimental feasibility of this quantum computing paradigm.
Geometric measure of quantum discord under decoherence
Xiao-Ming, Lu; Sun, Zhe; Wang, Xiaoguang
2010-01-01
The dynamics of a geometric measure of the quantum discord (GMQD) under decoherence is investigated. We show that the GMQD of a two-qubit state can be alternatively obtained through the singular values of a 3\\times4 matrix whose elements are the expectation values of Pauli matrices of the two qubits. By using Heisenberg picture, the analytic results of the GMQD is obtained for three typical kinds of the quantum decoherence channels. We compare the dynamics of the GMQD with that of the quantum discord and of entanglement and show that a sudden change in the decay rate of the GMQD does not always imply the sudden change in the decay rate of the quantum discord.
Interqubit coupling mediated by a high-excitation-energy quantum object
Ashhab, S.; Niskanen, A.O.; Harrabi, K.; Nakamura, Y.; Picot, T.; De Groot, P.C.; Harmans, C.J.P.M.; Mooij, J.E.; Nori, F.
2008-01-01
We consider a system composed of two qubits and a high excitation energy quantum object used to mediate coupling between the qubits. We treat the entire system quantum mechanically and analyze the properties of the eigenvalues and eigenstates of the total Hamiltonian. After reproducing well known re
Perfect Biparticle Teleportation by Using Multi-particle Quantum Channel with Joint Measurement
Institute of Scientific and Technical Information of China (English)
GUO Yan-Qing; NIE Jing; REN Zhong-Zhou; LI Chong; CHEN Yu-Qing; YI Xue-Xi
2008-01-01
In this paper, we reinvestigate the faithful quantum teleportation of an arbitrary two-qubit state by a multi-particle channel with multi-particle joint measurements. The relationship between multi-particle quantum channel and the multi-particle joint measurement bases has been found. In addition, we show how to construct the multi-particle joint measurement bases.
Man'ko, M. A.; Man'ko, V. I.
2016-03-01
We show that the density-matrix states of noncomposite qudit systems satisfy entropic and information relations like the subadditivity condition, strong subadditivity condition, and Araki-Lieb inequality, which characterize hidden quantum correlations of observables associated with these indivisible systems. We derive these relations employing a specific map of the entropic inequalities known for density matrices of multiqudit systems to the inequalities for density matrices of single-qudit systems. We present the obtained relations in the form of mathematical inequalities for arbitrary Hermitian N × N-matrices. We consider examples of superconducting qubits and qudits. We discuss the hidden correlations in single- qudit states as a new resource for quantum technologies analogous to the known resource in correlations associated with the entanglement in multiqudit systems.
Quantum Computation by Pairing Trapped Ultracold Ions
Institute of Scientific and Technical Information of China (English)
冯芒; 朱熙文; 高克林; 施磊
2001-01-01
Superpositional wavefunction oscillations for the implementation of quantum algorithms modify the desired interference required for the quantum computation. We propose a scheme with trapped ultracold ion-pairs beingqubits to diminish the detrimental effect of the wavefunction oscillations, which is applied to the two-qubitGrover's search. It can be also found that the qubits in our scheme are more robust against the decoherencecaused by the environment, and the model is scalable.
Quantum gates with topological phases
Ionicioiu, R
2003-01-01
We investigate two models for performing topological quantum gates with the Aharonov-Bohm (AB) and Aharonov-Casher (AC) effects. Topological one- and two-qubit Abelian phases can be enacted with the AB effect using charge qubits, whereas the AC effect can be used to perform all single-qubit gates (Abelian and non-Abelian) for spin qubits. Possible experimental setups suitable for a solid state implementation are briefly discussed.
An Introduction to Quantum Entanglement: a Geometric Approach
Zyczkowski, K; Zyczkowski, Karol; Bengtsson, Ingemar
2006-01-01
We present a concise introduction to quantum entanglement. Concentrating on bipartite systems we review the separability criteria and measures of entanglement. We focus our attention on geometry of the sets of separable and maximally entangled states. We treat in detail the two-qubit system and emphasise in what respect this case is a special one.
Stability of Mixed Nash Equilibria in Symmetric Quantum Games
Institute of Scientific and Technical Information of China (English)
A. Iqbal; A.H. Toor
2004-01-01
In bimatrix games the Bishop-Cannings theorem of the classical evolutionary game theory does not permitpure evolutionarily stable strategies (ESSs) when a mixed ESS exists. We find the necessary form of two-qubit initialquantum states when a switch-over to a quantum version of the game also changes the evolutionary stability of a mixedsymmetric Nash equilibrium.