Zhang, Nan; Fan, Zhaoyang; Luo, Nan; Bi, Xiaoming; Zhao, Yike; An, Jing; Liu, Jiayi; Chen, Zhong; Fan, Zhanming; Li, Debiao
2016-02-01
To evaluate the feasibility and diagnostic performance of flow-sensitive dephasing (FSD)-prepared steady-state free precession (SSFP) MR angiography (MRA) for imaging infragenual arteries at 3.0T, with contrast enhanced MR angiography (CE MRA) as reference. Twenty consecutive patients with suspicion of lower extremity arterial disease undergoing routine CE MRA were recruited. FSD MRA was performed at calf before CE MRA. Image quality and stenosis degree of infragenual arteries from both techniques were independently evaluated and compared. Six patients in this study underwent DSA examination. Three undiagnostic segments were excluded with severe venous contamination in CE MRA. A total of 197 calf arterial segments images were analyzed. No significant difference existed in the relative signal intensity (rSI) of arterial segments between FSD MRA and CE MRA techniques (0.92 ± 0.09 versus 0.93 ± 0.05; P = 0.207). However, the subjective image quality score was slightly higher in FSD MRA (3.66 ± 0.81 versus 3.49 ± 0.87; P = 0.050). With CE MRA images as reference standard, slight overestimation existed in FSD MRA (2.19 ± 1.24 versus 2.09 ± 1.18; P = 0.019), with total agreement of 84.3% on the basis of all arterial segments. The sensitivity, specificity, negative predictive value, and positive predictive value of FSD MRA was 96.4%, 93.0%, 98.5%, and 84.1%. No significant difference in the stenosis degree score was detected between MRA (FSD MRA and CE MRA) and DSA (P > 0.05). FSD MRA performed on at 3.0T without the use of contrast medium provides diagnostic images allowing for arterial stenosis assessment of calf arteries that was highly comparable with CE MRA. Moreover, venous contamination was less problematic with FSD MRA. © 2015 Wiley Periodicals, Inc.
Fan, Zhaoyang; Hodnett, Philip A; Davarpanah, Amir H; Scanlon, Timothy G; Sheehan, John J; Varga, John; Carr, James C; Li, Debiao
2011-08-01
: To develop a flow-sensitive dephasing (FSD) preparative scheme to facilitate multidirectional flow-signal suppression in 3-dimensional balanced steady-state free precession imaging and to validate the feasibility of the refined sequence for noncontrast magnetic resonance angiography (NC-MRA) of the hand. : A new FSD preparative scheme was developed that combines 2 conventional FSD modules. Studies using a flow phantom (gadolinium-doped water 15 cm/s) and the hands of 11 healthy volunteers (6 males and 5 females) were performed to compare the proposed FSD scheme with its conventional counterpart with respect to the signal suppression of multidirectional flow. In 9 of the 11 healthy subjects and 2 patients with suspected vasculitis and documented Raynaud phenomenon, respectively, 3-dimensional balanced steady-state free precession imaging coupled with the new FSD scheme was compared with spatial-resolution-matched (0.94 × 0.94 × 0.94 mm) contrast-enhanced magnetic resonance angiography (0.15 mmol/kg gadopentetate dimeglumine) in terms of overall image quality, venous contamination, motion degradation, and arterial conspicuity. : The proposed FSD scheme was able to suppress 2-dimensional flow signal in the flow phantom and hands and yielded significantly higher arterial conspicuity scores than the conventional scheme did on NC-MRA at the regions of common digitals and proper digitals. Compared with contrast-enhanced magnetic resonance angiography, the refined NC-MRA technique yielded comparable overall image quality and motion degradation, significantly less venous contamination, and significantly higher arterial conspicuity score at digital arteries. : The FSD-based NC-MRA technique is improved in the depiction of multidirectional flow by applying a 2-module FSD preparation, which enhances its potential to serve as an alternative magnetic resonance angiography technique for the assessment of hand vascular abnormalities.
International Nuclear Information System (INIS)
Zou Liqiu; Liu Xiaoyi; Liu Xin; Feng Fei; Qi Yulong; Liu Pengcheng
2011-01-01
Objective: To investigate balanced steady-state free precession with flow-sensitive dephasing magnetization preparation (FSD-bSSFP) in the assessment of arteries of foot in diabetic patients. Methods: The lower-extremity peripheral arteries of 43 diabetic patients were evaluated by FSD-bSSFP no contrast MRA and contrast-enhanced MRA (CE-MRA) in. Two experienced observers assessed the image quality, degree of venous contaminated and visibility of pedal artery branches by FSD-bSSFP and CE-MRA respectively in consensus. The signal intensity (SI), signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) of the source images of both groups were measured and Wilcoxon and t tests were performed. Results: The image score of FSD-bSSFP group was 2.7±1.1 and CE-MRA was 2.6±0.8, there was no statistical difference (Z= 0.134, P>0.05). The image score of demonstration of the pedal artery branches and degree of venous contamination on FSD-bSSFP were 3.2±0.9 and 1.8±0.4 respectively which were superior to that of CE-MRA (2.5±0.9 and 2.1±0.8 respectively). Significant statistical difference existed between the two groups in demonstration of pedal artery branches (Z=5.246, P 0.05). But CNR of CE-MRA was superior to that of FSD-bSSFP and significant statistical difference existed between these two methods (t=5.113, P<0.01). Conclusion: FSD-bSSFP without contrast could be used in the evaluation of foot arteries in patients of renal dysfunction and diabetes. (authors)
Universal dephasing control during quantum computation
International Nuclear Information System (INIS)
Gordon, Goren; Kurizki, Gershon
2007-01-01
Dephasing is a ubiquitous phenomenon that leads to the loss of coherence in quantum systems and the corruption of quantum information. We present a universal dynamical control approach to combat dephasing during all stages of quantum computation, namely, storage and single- and two-qubit operators. We show that (a) tailoring multifrequency gate pulses to the dephasing dynamics can increase fidelity; (b) cross-dephasing, introduced by entanglement, can be eliminated by appropriate control fields; (c) counterintuitively and contrary to previous schemes, one can increase the gate duration, while simultaneously increasing the total gate fidelity
Qubit dephasing due to quasiparticle tunneling
Energy Technology Data Exchange (ETDEWEB)
Zanker, Sebastian; Marthaler, Michael; Schoen, Gerd [Institut fuer Theoretische Festkoerperphysik, Karlsruhe Institute of Technology, D-76128 Karlsruhe (Germany)
2015-07-01
We study dephasing of a superconducting qubit due to quasiparticle tunneling through a Josephson junction. While qubit decay due to tunneling processes is well understood within a golden rule approximation, pure dephasing due to BCS quasiparticles gives rise to a divergent golden rule rate. We calculate qubit dephasing due to quasiparticle tunneling beyond lowest order approximation in coupling between qubit and quasiparticles. Summing up a certain class of diagrams we show that qubit dephasing due to purely longitudinal coupling to quasiparticles leads to dephasing ∝ exp(-x(t)) where x(t) ∝ t{sup 3/2} for short time scales and x(t) ∝ tlog(t) for long time scales.
Atomistic Galois insertions for flow sensitive integrity
DEFF Research Database (Denmark)
Nielson, Flemming; Nielson, Hanne Riis
2017-01-01
Several program verification techniques assist in showing that software adheres to the required security policies. Such policies may be sensitive to the flow of execution and the verification may be supported by combinations of type systems and Hoare logics. However, this requires user assistance...... and to obtain full automation we shall explore the over-approximating nature of static analysis. We demonstrate that the use of atomistic Galois insertions constitutes a stable framework in which to obtain sound and fully automatic enforcement of flow sensitive integrity. The framework is illustrated...
Coherence-generating power of quantum dephasing processes
Styliaris, Georgios; Campos Venuti, Lorenzo; Zanardi, Paolo
2018-03-01
We provide a quantification of the capability of various quantum dephasing processes to generate coherence out of incoherent states. The measures defined, admitting computable expressions for any finite Hilbert-space dimension, are based on probabilistic averages and arise naturally from the viewpoint of coherence as a resource. We investigate how the capability of a dephasing process (e.g., a nonselective orthogonal measurement) to generate coherence depends on the relevant bases of the Hilbert space over which coherence is quantified and the dephasing process occurs, respectively. We extend our analysis to include those Lindblad time evolutions which, in the infinite-time limit, dephase the system under consideration and calculate their coherence-generating power as a function of time. We further identify specific families of such time evolutions that, although dephasing, have optimal (over all quantum processes) coherence-generating power for some intermediate time. Finally, we investigate the coherence-generating capability of random dephasing channels.
Coherence and dephasing in self-assembled quantum dots
DEFF Research Database (Denmark)
Hvam, Jørn Märcher; Leosson, K.; Birkedal, Dan
2003-01-01
We measured dephasing times in InGaAl/As self-assembled quantum dots at low temperature using degenerate four-wave mixing. At 0K, the coherence time of the quantum dots is lifetime limited, whereas at finite temperatures pure dephasing by exciton-phonon interactions governs the quantum dot...
Dephasing in InAs/GaAs quantum dots
DEFF Research Database (Denmark)
Borri, Paola; Langbein, Wolfgang Werner; Mørk, Jesper
1999-01-01
The room-temperature dephasing in InAs/GaAs self-assembled quantum dots is measured using two independent methods: spectal-hole burning and four-wave mixing. Dephasing times weakly dependent on the excitation density are found, with a low density value of 290+/-80 fs from spectal-hole burning...
Dephasing of optically generated electron spins in semiconductors
International Nuclear Information System (INIS)
Idrish Miah, M.
2010-01-01
Dephasing of optically generated electron spins in the presence of the external magnetic field and electric bias in semiconductor nano-structures has been studied by time- and polarization-resolved spectrometry. The obtained experimental data are presented in dependence of the strength of the magnetic field. The optically generated electron-spin precession frequency and dephasing time and rate are estimated. It is found that both the spin precession frequency and dephasing rate increase linearly with the external magnetic field up to about 9 T. However, the spin dephasing time is within sub-μs and is found to decrease exponentially with the strength of the external magnetic field. The results are discussed by exploring possible mechanisms of spin dephasing in low-dimensional semiconductor structures, where the quantum-confinement persists within the nano-range.
Dephasing of optically generated electron spins in semiconductors
Energy Technology Data Exchange (ETDEWEB)
Idrish Miah, M., E-mail: m.miah@griffith.edu.a [Department of Physics, University of Chittagong, Chittagong, Chittagong - 4331 (Bangladesh)
2010-09-13
Dephasing of optically generated electron spins in the presence of the external magnetic field and electric bias in semiconductor nano-structures has been studied by time- and polarization-resolved spectrometry. The obtained experimental data are presented in dependence of the strength of the magnetic field. The optically generated electron-spin precession frequency and dephasing time and rate are estimated. It is found that both the spin precession frequency and dephasing rate increase linearly with the external magnetic field up to about 9 T. However, the spin dephasing time is within sub-{mu}s and is found to decrease exponentially with the strength of the external magnetic field. The results are discussed by exploring possible mechanisms of spin dephasing in low-dimensional semiconductor structures, where the quantum-confinement persists within the nano-range.
Financial Development and Investment-Cash Flow Sensitivity
Directory of Open Access Journals (Sweden)
Jungwon Suh
2007-06-01
Full Text Available Using firm-level data from thirty-five countries around the world, this paper empirically examines whether investment-cash flow sensitivity reflects financial constraints. Recent US studies have raised questions on the prediction that investment-cash flow sensitivity is a measure of financial constraints. Looking at thirty-five countries with varying degrees of financial development, this study tests whether investment-cash flow sensitivity is in fact related to financial constraints. In most countries, the evidence supporting the argument that firms likely facing financially constraints display high investment-cash flow sensitivity is weak. Moreover, the evidence that firms in the absence of developed financial markets display high investment-cash flow sensitivity is also weak. Overall, the results from this international investigation do not support the prediction that investment-cash flow sensitivity reflects financial constraints.
Many-Particle Dephasing after a Quench
Kiendl, Thomas; Marquardt, Florian
2017-03-01
After a quench in a quantum many-body system, expectation values tend to relax towards long-time averages. However, temporal fluctuations remain in the long-time limit, and it is crucial to study the suppression of these fluctuations with increasing system size. The particularly important case of nonintegrable models has been addressed so far only by numerics and conjectures based on analytical bounds. In this work, we are able to derive analytical predictions for the temporal fluctuations in a nonintegrable model (the transverse Ising chain with extra terms). Our results are based on identifying a dynamical regime of "many-particle dephasing," where quasiparticles do not yet relax but fluctuations are nonetheless suppressed exponentially by weak integrability breaking.
Quantum capacity of dephasing channels with memory
International Nuclear Information System (INIS)
D'Arrigo, A; Benenti, G; Falci, G
2007-01-01
We show that the amount of coherent quantum information that can be reliably transmitted down a dephasing channel with memory is maximized by separable input states. In particular, we model the channel as a Markov chain or a multimode environment of oscillators. While in the first model, the maximization is achieved for the maximally mixed input state, in the latter it is convenient to exploit the presence of a decoherence-protected subspace generated by memory effects. We explicitly compute the quantum channel capacity for the first model while numerical simulations suggest a lower bound for the latter. In both cases memory effects enhance the coherent information. We present results valid for arbitrary input size
Room-Temperature Dephasing in InAs Quantum Dots
DEFF Research Database (Denmark)
Borri, Paola; Langbein, Wolfgang; Mørk, Jesper
2000-01-01
The room temperature dephasing in InAs/InGaAs/GaAs self-assembled quantum dots, embedded in a waveguide for laser applications, is measured using two independent methods: spectral hole burning and four-wave mixing. Without the application of bias current for electrical carrier injection......, a dephasing time of ~260 fs, weakly dependent on the optical excitation density, is found and attributed to phonon interaction. The application of bias current, leading to population inversion in the dot ground state and optical gain, strongly decreases the dephasing time to less than 50 fs, likely due...
Dephasing and hyperfine interaction in carbon nanotubes double quantum dots
DEFF Research Database (Denmark)
Reynoso, Andres Alejandro; Flensberg, Karsten
2012-01-01
We study theoretically the return probability experiment, which is used to measure the dephasing time T-2*, in a double quantum dot (DQD) in semiconducting carbon nanotubes with spin-orbit coupling and disorder-induced valley mixing. Dephasing is due to hyperfine interaction with the spins of the C...... with these for DQDs in clean nanotubes, whereas the disorder effect is always relevant when the magnetic field is perpendicular to the nanotube axis....
Prisoners' dilemma in the presence of collective dephasing
International Nuclear Information System (INIS)
Nawaz, Ahmad
2012-01-01
We quantize prisoners' dilemma in the presence of collective dephasing with a dephasing rate γ. It is shown that for a two-parameter set of strategies, Q⊗Q is Nash equilibrium below a cut-off value of time. Beyond this cut-off it bifurcates into two new Nash equilibria Q⊗D and D⊗Q. Furthermore, for the maximum value of decoherence C⊗D and D⊗C also become Nash equilibria. At this stage the game has four Nash equilibria. On the other hand, for a three-parameter set of strategies, there is no pure strategy Nash equilibrium; however, there is a mixed strategy (non-unique) Nash equilibrium that is not affected by collective dephasing. (paper)
Magneto-exciton dephasing in a single quantum dot
Rodriguez, F. J.; Reyes, A.; Olaya-Castro, A.; Quiroga, L.
2001-03-01
Ultrafast spectroscopy experiments on single quantum dot (SQD) in magnetic fields provide a variety of unexpected results, one of them being the recently reported entanglement of exciton states. In order to explore the entanglement robustness, dephasing mechanisms must be considered. By calculating the non-linear time resolved optical spectrum of a SQD, we present a theoretical study on the exciton-exciton scattering contribution to the magneto-exciton dephasing time. Our results show that the time evolution of \\chi^(3) presents, under non-steady-state condition, a beating between the bound biexciton and the first unbound biexciton state in the strong confinement regime. The contribution coming from both left and right polarized emitted photons allows us to predict the creation of exciton entanglement, in agreement with recent experimental results. Previous theoretical works have only addressed the stationary optical response. By contrast, our results based on a full time dependent calculation show new features specially for the fast dephasing case.
A comparative study of two phenomenological models of dephasing in series and parallel resistors
International Nuclear Information System (INIS)
Bandopadhyay, Swarnali; Chaudhuri, Debasish; Jayannavar, Arun M.
2010-01-01
We compare two recent phenomenological models of dephasing using a double barrier and a quantum ring geometry. While the stochastic absorption model generates controlled dephasing leading to Ohm's law for large dephasing strengths, a Gaussian random phase based statistical model shows many inconsistencies.
Resonance Raman and optical dephasing study of tricarbocyanine dyes
Ashworth, SH; Kummrow, A; Lenz, K
Fluorescence lineshape analysis based on resonance Raman spectra of the dye HITCI was used to determine the details and magnitude of the vibrational part of the line broadening function, Forced light scattering (FLS) was applied to measure optical dephasing of HITCI in ethylene glycol, pumping at
Wave attenuation model for dephasing and measurement of ...
Indian Academy of Sciences (India)
There are different ways to model dephasing in mesoscopic systems. An interesting method is to attach a voltage probe [3] to the sample as in the inset of figure 1 (Buttiker's model). In this model, an electron captured by a voltage probe is injected back with an uncorrelated phase leading to irreversible loss of phase memory ...
Exciton dephasing in ZnSe quantum wires
DEFF Research Database (Denmark)
Wagner, Hans Peter; Langbein, Wolfgang Werner; Hvam, Jørn Märcher
1998-01-01
The homogeneous linewidths of excitons in wet-etched ZnSe quantum wires of lateral sizes down to 23 nm are studied by transient four-wave mixing. The low-density dephasing time is found to increase with decreasing wire width. This is attributed mainly to a reduction of electron-exciton scattering...
Binding-energy distribution and dephasing of localized biexcitons
DEFF Research Database (Denmark)
Langbein, Wolfgang Werner; Hvam, Jørn Märcher; Umlauff, M.
1997-01-01
We report on the binding energy and dephasing of localized biexciton states in narrow ZnSe multiple quantum wells. The measured binding-energy distribution of the localized biexcitons shows a width of 2.2 meV centered at 8.5 meV, and is fairly independent of the exciton localization energy. In fo...
Influence of pure dephasing on emission spectra from single photon sources
DEFF Research Database (Denmark)
Næsby Rasmussen, Andreas; Skovgård, Troels Suhr; Kristensen, Philip Trøst
2008-01-01
We investigate the light-matter interaction of a quantum dot with the electromagnetic field in a lossy microcavity and calculate emission spectra for nonzero detuning and dephasing. It is found that dephasing shifts the intensity of the emission peaks for nonzero detuning. We investigate the char......We investigate the light-matter interaction of a quantum dot with the electromagnetic field in a lossy microcavity and calculate emission spectra for nonzero detuning and dephasing. It is found that dephasing shifts the intensity of the emission peaks for nonzero detuning. We investigate...
Dephasing in self-organized InAlGaAs quantum dots
DEFF Research Database (Denmark)
Leosson, K.; Birkedal, Dan; Hvam, Jørn Märcher
2002-01-01
We report the first direct measurements of dephasing in III-V semiconductor quantum dots at low temperature using degenerate four-wave mixing. At OK, the coherence time is limited by the population lifetime whereas pure dephasing due to exciton-phonon interactions appears only at finite temperatu......We report the first direct measurements of dephasing in III-V semiconductor quantum dots at low temperature using degenerate four-wave mixing. At OK, the coherence time is limited by the population lifetime whereas pure dephasing due to exciton-phonon interactions appears only at finite...
Dephasing times in quantum dots due to elastic LO phonon-carrier collisions
DEFF Research Database (Denmark)
Uskov, A. V.; Jauho, Antti-Pekka; Tromborg, Bjarne
2000-01-01
Interpretation of experiments on quantum dot (QD) lasers presents a challenge: the phonon bottleneck, which should strongly suppress relaxation and dephasing of the discrete energy states, often seems to be inoperative. We suggest and develop a theory for an intrinsic mechanism for dephasing in Q......: second-order elastic interaction between quantum dot charge carriers and LO phonons. The calculated dephasing times are of the order of 200 fs at room temperature, consistent with experiments. The phonon bottleneck thus does not prevent significant room temperature dephasing....
Dephasing in coherent communication with weak signal states
International Nuclear Information System (INIS)
Jarzyna, Marcin; Banaszek, Konrad; Demkowicz-Dobrzański, Rafał
2014-01-01
We analyse the ultimate quantum limit on the accessible information for an optical communication scheme when time bins carry coherent light pulses prepared in one of several orthogonal modes and the phase undergoes diffusion after each channel use. This scheme, an example of a quantum memory channel, can be viewed as noisy pulse position modulation (PPM) keying with phase fluctuations occurring between consecutive PPM symbols. We derive a general expression for the output states in the Fock basis and implement a numerical procedure to calculate the Holevo quantity. Using asymptotic properties of Toeplitz matrices, we also present an analytic expression for the Holevo quantity valid for very weak signals and sufficiently strong dephasing when the dominant contribution comes from the single-photon sector in the Hilbert space of signal states. Based on numerical results we conjecture an inequality for contributions to the Holevo quantity from multiphoton sectors which implies that in the asymptotic limit of weak signals, for arbitrarily small dephasing the accessible information scales linearly with the average number of photons contained in the pulse. Such behaviour presents a qualitative departure from the fully coherent case. (paper)
Spin-Dephasing Anisotropy for Electrons in a Diffusive Quasi-1D GaAs Wire
Liu, J.; Last, T.; Koop, E. J.; Denega, S.; van Wees, B. J.; van der Wal, C. H.
We present a numerical study of dephasing of electron spin ensembles in a diffusive quasi-one-dimensional GaAs wire due to the D'yakonov-Perel' spin-dephasing mechanism. For widths of the wire below the spin precession length and for equal strength of Rashba and linear Dresselhaus spin-orbit fields
Dephasing in semiconductor-superconductor structures by coupling to a voltage probe
DEFF Research Database (Denmark)
Mortensen, Niels Asger; Jauho, Antti-Pekka; Flensberg, Karsten
2000-01-01
We study dephasing in semiconductor-superconductor structures caused by coupling to a voltage probe. We consider structures where the semiconductor consists of two scattering regions between which partial dephasing is possible. As a particular example we consider a situation with a double barrier...
Exciton dephasing and biexciton binding in CdSe/ZnSe islands
DEFF Research Database (Denmark)
Wagner, Hans Peter; Tranitz, H.-P.; Preis, H
1999-01-01
The dephasing of excitons and the formation of biexcitons in self-organized CdSe/ZnSe islands grown by molecular-beam epitaxy is investigated using spectrally resolved four-wave mixing. A distribution of exciton-exciton scattering efficiencies and dephasing times in the range of 0.5-10 ps...
Heat transport in the XXZ spin chain: from ballistic to diffusive regimes and dephasing enhancement
International Nuclear Information System (INIS)
Mendoza-Arenas, J J; Al-Assam, S; Clark, S R; Jaksch, D
2013-01-01
In this work we study the heat transport in an XXZ spin-1/2 Heisenberg chain with homogeneous magnetic field, incoherently driven out of equilibrium by reservoirs at the boundaries. We focus on the effect of bulk dephasing (energy-dissipative) processes in different parameter regimes of the system. The non-equilibrium steady state of the chain is obtained by simulating its evolution under the corresponding Lindblad master equation, using the time evolving block decimation method. In the absence of dephasing, the heat transport is ballistic for weak interactions, while being diffusive in the strongly interacting regime, as evidenced by the heat current scaling with the system size. When bulk dephasing takes place in the system, diffusive transport is induced in the weakly interacting regime, with the heat current monotonically decreasing with the dephasing rate. In contrast, in the strongly interacting regime, the heat current can be significantly enhanced by dephasing for systems of small size. (paper)
Temporal fluctuations after a quantum quench: Many-particle dephasing
Marquardt, Florian; Kiendl, Thomas
After a quantum quench, the expectation values of observables continue to fluctuate in time. In the thermodynamic limit, one expects such fluctuations to decrease to zero, in order for standard statistical physics to hold. However, it is a challenge to determine analytically how the fluctuations decay as a function of system size. So far, there have been analytical predictions for integrable models (which are, naturally, somewhat special), analytical bounds for arbitrary systems, and numerical results for moderate-size systems. We have discovered a dynamical regime where the decrease of fluctuations is driven by many-particle dephasing, instead of a redistribution of occupation numbers. On the basis of this insight, we are able to provide exact analytical expressions for a model with weak integrability breaking (transverse Ising chain with additional terms). These predictions explicitly show how fluctuations are exponentially suppressed with system size.
Quantum correlation of high dimensional system in a dephasing environment
Ji, Yinghua; Ke, Qiang; Hu, Juju
2018-05-01
For a high dimensional spin-S system embedded in a dephasing environment, we theoretically analyze the time evolutions of quantum correlation and entanglement via Frobenius norm and negativity. The quantum correlation dynamics can be considered as a function of the decoherence parameters, including the ratio between the system oscillator frequency ω0 and the reservoir cutoff frequency ωc , and the different environment temperature. It is shown that the quantum correlation can not only measure nonclassical correlation of the considered system, but also perform a better robustness against the dissipation. In addition, the decoherence presents the non-Markovian features and the quantum correlation freeze phenomenon. The former is much weaker than that in the sub-Ohmic or Ohmic thermal reservoir environment.
Exciton dephasing in single InGaAs quantum dots
DEFF Research Database (Denmark)
Leosson, Kristjan; Østergaard, John Erland; Jensen, Jacob Riis
2000-01-01
The homogeneous linewidth of excitonic transitions is a parameter of fundamental physical importance. In self-assembled quantum dot systems, a strong inhomogeneous broadening due to dot size fluctuations masks the homogeneous linewidth associated with transitions between individual states....... The homogeneous and inhomogeneous broadening of InGaAs quantum dot luminescence is of central importance for the potential application of this material system in optoelectronic devices. Recent measurements of MOCVD-grown InAs/InGaAs quantum dots indicate a large homogeneous broadening at room temperature due...... to fast dephasing. We present an investigation of the low-temperature homogeneous linewidth of individual PL lines from MBE-grown In0.5Ga0.5As/GaAs quantum dots....
General solution to inhomogeneous dephasing and smooth pulse dynamical decoupling
Zeng, Junkai; Deng, Xiu-Hao; Russo, Antonio; Barnes, Edwin
2018-03-01
In order to achieve the high-fidelity quantum control needed for a broad range of quantum information technologies, reducing the effects of noise and system inhomogeneities is an essential task. It is well known that a system can be decoupled from noise or made insensitive to inhomogeneous dephasing dynamically by using carefully designed pulse sequences based on square or delta-function waveforms such as Hahn spin echo or CPMG. However, such ideal pulses are often challenging to implement experimentally with high fidelity. Here, we uncover a new geometrical framework for visualizing all possible driving fields, which enables one to generate an unlimited number of smooth, experimentally feasible pulses that perform dynamical decoupling or dynamically corrected gates to arbitrarily high order. We demonstrate that this scheme can significantly enhance the fidelity of single-qubit operations in the presence of noise and when realistic limitations on pulse rise times and amplitudes are taken into account.
Constraints on dephasing widths and shifts in three-level quantum systems
International Nuclear Information System (INIS)
Berman, P.R.; O'Connell, Ross C.
2005-01-01
It is shown that the density matrix equations for a three-level quantum system interacting with external radiation fields can lead to negative populations if arbitrary dephasing rates and shifts are included in these equations. To guarantee non-negative populations, the equations themselves impose certain restrictions on the dephasing widths and shifts. The constraints on the widths are shown to be identical to those that can be derived from a model of Markovian dephasing events, independent of any atom-field interaction
Feedback controlled dephasing and population relaxation in a two-level system
International Nuclear Information System (INIS)
Wang Jin
2009-01-01
This Letter presents the maximum achievable stability and purity that can be obtained in a two-level system with both dephasing and population relaxation processes by using homodyne-mediated feedback control. An analytic formula giving the optimal amplitudes of the driving and feedback for the steady-state is also presented. Experimental examples are used to show the importance of controlling the dephasing process.
George, R.; Kabir, Mohammed Rezaul; Qian, J.
2011-01-01
A controversy exists on the use of the investment–cash flow sensitivity as a measure of financing constraints of firms.Were-examine this controversy by analyzing firms affiliated to Indian business groups. We find a strong investment–cash flow sensitivity for both group-affiliated and independent
Investment cash flow sensitivity under managerial optimism: new evidence from NYSE panel data firms
Mohamed, Ezzeddine Ben; Fairchild, Richard; Bouri, Abdelfettah
2014-01-01
Investment cash flow sensitivity constitutes one important block of the corporate financial literature. While it is well documented in standard corporate finance, it is still young under behavioral corporate finance. In this paper, we test the investment cash flow sensitivity among panel data of American industrial firms during 1999-2010. Using Q-model of investment (Tobin, 1969), we construct and introduce a proxy of managerial optimism following Malmendier and Tate (2005a) to show the impac...
Factors affecting the effectiveness of a projection dephaser in 2D gradient-echo imaging
International Nuclear Information System (INIS)
Bakker, Chris J G; Peters, Nicky H G M; Vincken, Koen L; Bom, Martijn van der; Seppenwoolde, Jan-Henry
2007-01-01
Projection dephasers are often used for background suppression and dynamic range improvement in thick-slab 2D imaging in order to promote the visibility of subslice structures, e.g., blood vessels and interventional devices. In this study, we explored the factors that govern the effectiveness of a projection dephaser by simulations and phantom experiments. This was done for the ideal case of a single subslice hyper- or hypointensity against a uniform background in the absence of susceptibility effects. Simulations and experiments revealed a pronounced influence of the slice profile, the nominal flip angle and the TE and TR of the acquisition, the size, intraslice position and MR properties of the subslice structure, and T 1 of the background. The complexity of the ideal case points to the necessity of additional explorations when considering the use of projection dephasers under less ideal conditions, e.g., in the presence of tissue heterogeneities and susceptibility gradients
Energy Technology Data Exchange (ETDEWEB)
Kahnoj, Sina Soleimani; Touski, Shoeib Babaee [School of Electrical and Computer Engineering, University of Tehran, P.O. Box 14395-515, Tehran (Iran, Islamic Republic of); Pourfath, Mahdi, E-mail: pourfath@ut.ac.ir, E-mail: pourfath@iue.tuwien.ac.at [School of Electrical and Computer Engineering, University of Tehran, P.O. Box 14395-515, Tehran (Iran, Islamic Republic of); Institute for Microelectronics, TU Wien, Gusshausstrasse 27–29/E360, 1040 Vienna (Austria)
2014-09-08
The effect of dephasing induced by electron-electron interaction on electronic transport in graphene nanoribbons is theoretically investigated. In the presence of disorder in graphene nanoribbons, wavefunction of electrons can set up standing waves along the channel and the conductance exponentially decreases with the ribbon's length. Employing the non-equilibrium Green's function formalism along with an accurate model for describing the dephasing induced by electron-electron interaction, we show that this kind of interaction prevents localization and transport of electrons remains in the diffusive regime where the conductance is inversely proportional to the ribbon's length.
Spatial correlation in matter-wave interference as a measure of decoherence, dephasing, and entropy
Chen, Zilin; Beierle, Peter; Batelaan, Herman
2018-04-01
The loss of contrast in double-slit electron diffraction due to dephasing and decoherence processes is studied. It is shown that the spatial intensity correlation function of diffraction patterns can be used to distinguish between dephasing and decoherence. This establishes a measure of time reversibility that does not require the determination of coherence terms of the density matrix, while von Neumann entropy, another measure of time reversibility, does require coherence terms. This technique is exciting in view of the need to understand and control the detrimental experimental effect of contrast loss and for fundamental studies on the transition from the classical to the quantum regime.
Dissipation, dephasing and quantum Darwinism in qubit systems with random unitary interactions
Balaneskovic, Nenad; Mendler, Marc
2016-09-01
We investigate the influence of dissipation and decoherence on quantum Darwinism by generalizing Zurek's original qubit model of decoherence and the establishment of pointer states [W.H. Zurek, Nat. Phys. 5, 181 (2009); see also arXiv: quant-ph/0707.2832v1, pp. 14-19.]. Our model allows for repeated multiple qubit-qubit couplings between system and environment which are described by randomly applied two-qubit quantum operations inducing entanglement, dissipation and dephasing. The resulting stationary qubit states of system and environment are investigated. They exhibit the intricate influence of entanglement generation, dissipation and dephasing on this characteristic quantum phenomenon.
Reducing dephasing in coupled quantum dot-cavity systems by engineering the carrier wavefunctions
DEFF Research Database (Denmark)
Nysteen, Anders; Nielsen, Per Kær; Mørk, Jesper
2012-01-01
We demonstrate theoretically how photon-assisted dephasing by the electron-phonon interaction in a coupled cavity-quantum dot system can be significantly reduced for specific QD-cavity detunings. Our starting point is a recently published theory,1 which considers longitudinal acoustic phonons......, described by a non-Markovian model, interacting with a coupled quantum dot-cavity system. The reduction of phonon-induced dephasing is obtained by placing the cavity-quantum dot system inside an infinite slab, assuming spherical electronic wavefunctions. Based on our calculations, we expect this to have...
Rapid adiabatic passage in quantum dots: Influence of scattering and dephasing
DEFF Research Database (Denmark)
Schuh, K.; Jahnke, F.; Lorke, Michael
2011-01-01
Theoretical investigations for the realization of population inversion of semiconductor quantum dot ground-state transitions by means of adiabatic passage with chirped optical pulses are presented. While the inversion due to Rabi oscillations depends sensitively on the resonance condition...... to describe carrier scattering and dephasing in the corresponding simulations and allow to quantify the conditions to simultaneously invert an ensamble of quantum dots....
DEFF Research Database (Denmark)
Lundeman, Jesper Holm; Jensen, Ole Bjarlin; Andersen, Peter E.
2009-01-01
We present a measurement series of the efficiency of periodically poled KTP used for second-harmonic generation in an external phase-locked cavity. Due to the high absorption (0.01 cm^−1) in the PPKTP crystal at the pump wavelength a strong thermal dephasing of the periodically poled grating...
Datta, Anjali; Cheng, Joseph Y; Hargreaves, Brian A; Baron, Corey A; Nishimura, Dwight G
2018-06-01
To mitigate artifacts from through-plane flow at the locations of steady-state stopbands in balanced steady-state free precession (SSFP) using partial dephasing. A 60° range in the phase accrual during a TR was created over the voxel by slightly unbalancing the slice-select dephaser. The spectral profiles of SSFP with partial dephasing for various constant flow rates and during pulsatile flow were simulated to determine if partial dephasing decreases through-plane flow artifacts originating near SSFP dark bands while maintaining on-resonant signal. Simulations were then validated in a flow phantom. Lastly, phase-cycled SSFP cardiac cine images were acquired with and without partial dephasing in six subjects. Partial dephasing decreased the strength and non-linearity of the dependence of the signal at the stopbands on the through-plane flow rate. It thus mitigated hyper-enhancement from out-of-slice signal contributions and transient-related artifacts caused by variable flow both in the phantom and in vivo. In six volunteers, partial dephasing noticeably decreased artifacts in all of the phase-cycled cardiac cine datasets. Partial dephasing can mitigate the flow artifacts seen at the stopbands in balanced SSFP while maintaining the sequence's desired signal. By mitigating hyper-enhancement and transient-related artifacts originating from the stopbands, partial dephasing facilitates robust multiple-acquisition phase-cycled SSFP in the heart. Magn Reson Med 79:2944-2953, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.
Sun, Qi-C.; Ding, Yuchen; Goodman, Samuel M.; H. Funke, Hans; Nagpal, Prashant
2014-10-01
Copper metal can provide an important alternative for the development of efficient, low-cost and low-loss plasmonic nanoparticles, and selective nanocatalysts. However, poor chemical stability and lack of insight into photophysics and plasmon decay mechanisms has impeded study. Here, we use smooth conformal ALD coating on copper nanoparticles to prevent surface oxidation, and study dephasing time for localized surface plasmons on different sized copper nanoparticles. Using dephasing time as a figure of merit, we elucidate the role of electron-electron, electron-phonon, impurity, surface and grain boundary scattering on the decay of localized surface plasmon waves. Using our quantitative analysis and different temperature dependent measurements, we show that electron-phonon interactions dominate over other scattering mechanisms in dephasing plasmon waves. While interband transitions in copper metal contributes substantially to plasmon losses, tuning surface plasmon modes to infrared frequencies leads to a five-fold enhancement in the quality factor. These findings demonstrate that conformal ALD coatings can improve the chemical stability for copper nanoparticles, even at high temperatures (>300 °C) in ambient atmosphere, and nanoscaled copper is a good alternative material for many potential applications in nanophotonics, plasmonics, catalysis and nanoscale electronics.Copper metal can provide an important alternative for the development of efficient, low-cost and low-loss plasmonic nanoparticles, and selective nanocatalysts. However, poor chemical stability and lack of insight into photophysics and plasmon decay mechanisms has impeded study. Here, we use smooth conformal ALD coating on copper nanoparticles to prevent surface oxidation, and study dephasing time for localized surface plasmons on different sized copper nanoparticles. Using dephasing time as a figure of merit, we elucidate the role of electron-electron, electron-phonon, impurity, surface and grain
Relaxometry and Dephasing Imaging of Superparamagnetic Magnetite Nanoparticles Using a Single Qubit
Schmid-Lorch, Dominik; Häberle, Thomas; Reinhard, Friedemann; Zappe, Andrea; Slota, Michael; Bogani, Lapo; Finkler, Amit; Wrachtrup, Jörg
2015-08-01
To study the magnetic dynamics of superparamagnetic nanoparticles we use scanning probe relaxometry and dephasing of the nitrogen-vacancy (NV) center in diamond, characterizing the spin-noise of a single 10-nm magnetite particle. Additionally, we show the anisotropy of the NV sensitivity's dependence on the applied decoherence measurement method. By comparing the change in relaxation (T 1 ) and dephasing (T 2 ) time in the NV center when scanning a nanoparticle over it, we are able to extract the nanoparticle's diameter and distance from the NV center using an Ornstein-Uhlenbeck model for the nanoparticle's fluctuations. This scanning-probe technique can be used in the future to characterize different spin label substitutes for both medical applications and basic magnetic nanoparticle behavior.
International Nuclear Information System (INIS)
Burr, G.W.; Harris, Todd L.; Babbitt, Wm. Randall; Jefferson, C. Michael
2004-01-01
We describe the incorporation of excitation-induced dephasing (EID) into the Maxwell-Bloch numerical simulation of photon echoes. At each time step of the usual numerical integration, stochastic frequency jumps of ions--caused by excitation of neighboring ions--is modeled by convolving each Bloch vector with the Bloch vectors of nearby frequency detunings. The width of this convolution kernel follows the instantaneous change in overall population, integrated over the simulated bandwidth. This approach is validated by extensive comparison against published and original experimental results. The enhanced numerical model is then used to investigate the accuracy of experiments designed to extrapolate to the intrinsic dephasing time T 2 from data taken in the presence of EID. Such a modeling capability offers improved understanding of experimental results, and should allow quantitative analysis of engineering tradeoffs in realistic optical coherent transient applications
Vibronic dephasing model for coherent-to-incoherent crossover in DNA
Karasch, Patrick; Ryndyk, Dmitry A.; Frauenheim, Thomas
2018-05-01
In this paper, we investigate the interplay between coherent and incoherent charge transport in cytosine-guanine (GC-) rich DNA molecules. Our objective is to introduce a physically grounded approach to dephasing in large molecules and to understand the length-dependent charge transport characteristics, and especially the crossover from the coherent tunneling to incoherent hopping regime at different temperatures. Therefore, we apply the vibronic dephasing model and compare the results to the Büttiker probe model which is commonly used to describe decoherence effects in charge transport. Using the full ladder model and simplified one-dimensional model of DNA, we consider molecular junctions with alternating and stacked GC sequences and compare our results to recent experimental measurements.
Raman study of vibrational dephasing in liquid CH3CN and CD3CN
International Nuclear Information System (INIS)
Schroeder, J.; Schiemann, V.H.; Sharko, P.T.; Jonas, J.
1977-01-01
The Raman line shapes of the ν 1 (a 1 ) C--H and C--D fundamentals in liquid acetonitrile and acetonitrile-d 3 have been measured as a function of pressure up to 4 kbar within the temperature interval 30--120 degreeC. Densities have also been determined. From the isotropic component of the vibrational Raman band shape the vibrational relaxation times have been obtained as a function of temperature and pressure (density). The experimental results can be summarized as follows: (i) as T increases at constant density rho, the vibrational relaxation rate (tau/sub vib/) -1 increases; (ii) at constant T as density is raised tau/sub vib/ -1 increases; (iii) at constant pressure the T increase produces higher tau/sub vib/ -1 , however, the change is more pronounced for the CD 3 CN liquid. Isotopic dilution studies of the CH 3 CN/CD 3 CN mixtures shows no significant effect on (tau/sub vib/ -1 ). The experimental data are interpreted in terms of the Kubo stochastic line shape theory and the dephasing model of Fischer and Laubereau. The results based on Kubo formalism indicate that dephasing is the dominant relaxation mechanism and that the modulation is fast. The isolated binary collision model proposed by Fischer and Laubereau for vibrational dephasing reproduces the essential features of the density and temperature dependence of the (tau/sub vib/) -1 and suggests that pure dephasing is the dominant broadening mechanism for the isotropic line shapes studied. In the calculation the elastic collision times were approximated by the Enskog relaxation times
Time-resolved photoelectron spectrometry of a dephasing process in pyrazine
International Nuclear Information System (INIS)
Pavlov, R.L.; Pavlov, L.I.; Delchev, Ya.I.; Pavlova, S.I.
2001-01-01
The first femtosecond time-resolved photoelectron imaging (PEI) is presented. The method is characterized by photoionization of NO and further applied to ultrafast dephasing in pyrazine. Intermediate case behaviour in radiationless transition is clearly observed in time-resolved photoelectron kinetic energy distribution. Femtosecond PEI is with much improved efficiency than conventional photoelectron spectroscopies. It is anticipated that the unifield approach of time-resolved photoelectron and photoion imaging opens the possibility of observing photon-induced dynamics in real time
Dynamical decoupling sequences for multi-qubit dephasing suppression and long-time quantum memory
International Nuclear Information System (INIS)
Paz-Silva, Gerardo A; Lee, Seung-Woo; Green, Todd J; Viola, Lorenza
2016-01-01
We consider a class of multi-qubit dephasing models that combine classical noise sources and linear coupling to a bosonic environment, and are controlled by arbitrary sequences of dynamical decoupling pulses. Building on a general transfer filter-function framework for open-loop control, we provide an exact representation of the controlled dynamics for arbitrary stationary non-Gaussian classical and quantum noise statistics, with analytical expressions emerging when all dephasing sources are Gaussian. This exact characterization is used to establish two main results. First, we construct multi-qubit sequences that ensure maximum high-order error suppression in both the time and frequency domain and that can be exponentially more efficient than existing ones in terms of total pulse number. Next, we show how long-time multi-qubit storage may be achieved by meeting appropriate conditions for the emergence of a fidelity plateau under sequence repetition, thereby generalizing recent results for single-qubit memory under Gaussian dephasing. In both scenarios, the key step is to endow multi-qubit sequences with a suitable displacement anti-symmetry property, which is of independent interest for applications ranging from environment-assisted entanglement generation to multi-qubit noise spectroscopy protocols. (paper)
Quantum Metrology beyond the Classical Limit under the Effect of Dephasing
Matsuzaki, Yuichiro; Benjamin, Simon; Nakayama, Shojun; Saito, Shiro; Munro, William J.
2018-04-01
Quantum sensors have the potential to outperform their classical counterparts. For classical sensing, the uncertainty of the estimation of the target fields scales inversely with the square root of the measurement time T . On the other hand, by using quantum resources, we can reduce this scaling of the uncertainty with time to 1 /T . However, as quantum states are susceptible to dephasing, it has not been clear whether we can achieve sensitivities with a scaling of 1 /T for a measurement time longer than the coherence time. Here, we propose a scheme that estimates the amplitude of globally applied fields with the uncertainty of 1 /T for an arbitrary time scale under the effect of dephasing. We use one-way quantum-computing-based teleportation between qubits to prevent any increase in the correlation between the quantum state and its local environment from building up and have shown that such a teleportation protocol can suppress the local dephasing while the information from the target fields keeps growing. Our method has the potential to realize a quantum sensor with a sensitivity far beyond that of any classical sensor.
Pawlina, G.; Renneboog, L.D.R.
2005-01-01
We investigate the investment-cash flow sensitivity of a large sample of the UK listed firms and confirm that investment is strongly cash flow-sensitive.Is this suboptimal investment policy the result of agency problems when managers with high discretion overinvest, or of asymmetric information when
International Nuclear Information System (INIS)
Kang, Da-wei; Sun, Meng-le; Zuo, Zheng-wei; Wang, Hui-xian; Lv, Shi-jie; Li, Xin-zhong; Li, Li-ben
2016-01-01
The charge transport properties of the G4-DNA molecular device in the presence of counter ions and dephasing effect are investigated based on the Green function method and Landauer–Büttiker theory. The currents through the G4-DNA molecular device depend on the interference patterns at different coupling configurations. There is an effective electrostatic interaction between the counter ions and the G4-DNA molecule which introduces disorder into the on-site energies of G bases. The current through the device can be enhanced by the small disorder which avoids the strong interference of electrons at the same energy in some coupling configurations, however the diagonal disorder can suppress the overall current due to the Anderson localization of charge carriers when the disorder is large. In the presence of dephasing effect the current through the device at all coupling configurations can be enhanced as a result of the phase coherence losing of electron. As for the magnetic field response, the magnetoresistance of the device is always suppressed by the counter ions and dephasing effect. - Highlights: • The counter ions can some times enhance the current through G4-DNA molecule. • The dephasing effect can enhance the current of the device at all four coupling configurations. • The magnetoresistance is always suppressed by the counter ions and dephasing effect.
Reducing pure dephasing of quantum bits by collective encoding in quantum dot arrays
International Nuclear Information System (INIS)
Grodecka, A; Machnikowski, P; Jacak, L
2006-01-01
We show that phonon-induced pure dephasing of an excitonic (charge) quantum bit in a quantum dot (QD) may be reduced by collective encoding of logical qubits in QD arrays. We define the logical qubit on an array of 2, 4 and 8 QDs, connecting the logical 0) state with the presence of excitons in the appropriately chosen half of dots and the logical 1) state with the other half of the dots occupied. We give quantitative estimates of the resulting total error of a single qubit operation for an InAs/GaAs system
Hole dephasing caused by hole-hole interaction in a multilayered black phosphorus.
Li, Lijun; Khan, Muhammad Atif; Lee, Yoontae; Lee, Inyeal; Yun, Sun Jin; Youn, Doo-Hyeb; Kim, Gil-Ho
2017-11-01
We study the magnetotransport of holes in a multilayered black phosphorus in a temperature range of 1.9 to 21.5 K. We observed a negative magnetoresistance at magnetic fields up to 1.5 T. This negative magetoresistance was analyzed by weak localization theory in diffusive regime. At the lowest temperature and the highest carrier density we found a phase coherence length of 48 nm. The linear temperature dependence of the dephasing rate shows that the hole-hole scattering processes with small energy transfer are the dominant contribution in breaking the carrier phase coherence.
Ultrafast Dephasing and Incoherent Light Photon Echoes in Organic Amorphous Systems
Yano, Ryuzi; Matsumoto, Yoshinori; Tani, Toshiro; Nakatsuka, Hiroki
1989-10-01
Incoherent light photon echoes were observed in organic amorphous systems (cresyl violet in polyvinyl alcohol and 1,4-dihydroxyanthraquinone in polymethacrylic acid) by using temporally-incoherent nanosecond laser pulses. It was found that an echo decay curve of an organic amorphous system is composed of a sharp peak which decays very rapidly and a slowly decaying wing at the tail. We show that the persistent hole burning (PHB) spectra were reproduced by the Fourier-cosine transforms of the echo decay curves. We claim that in general, we must take into account the multi-level feature of the system in order to explain ultrafast dephasing at very low temperatures.
Semiclassical Monte Carlo simulation studies of spin dephasing in InP and InSb nanowires
Directory of Open Access Journals (Sweden)
Ashish Kumar
2012-03-01
Full Text Available We use semiclassical Monte Carlo approach to investigate spin polarized transport in InP and InSb nanowires. D’yakonov-Perel (DP relaxation and Elliott-Yafet (EY relaxation are the two main relaxation mechanisms for spin dephasing in III-V channels. The DP relaxation occurs because of bulk inversion asymmetry (Dresselhaus spin-orbit interaction and structural inversion asymmetry (Rashba spin-orbit interaction. The injection polarization direction studied is that along the length of the channel. The dephasing rate is found to be very strong for InSb as compared to InP which has larger spin dephasing lengths. The ensemble averaged spin components vary differently for both InP and InSb nanowires. The steady state spin distribution also shows a difference between the two III-V nanowires.
Towards optimized suppression of dephasing in systems subject to pulse timing constraints
International Nuclear Information System (INIS)
Hodgson, Thomas E.; D'Amico, Irene; Viola, Lorenza
2010-01-01
We investigate the effectiveness of different dynamical decoupling protocols for storage of a single qubit in the presence of a purely dephasing bosonic bath, with emphasis on comparing quantum coherence preservation under uniform versus nonuniform delay times between pulses. In the limit of instantaneous bit-flip pulses, this is accomplished by establishing a different representation of the controlled qubit evolution, where the decoherence behavior after an arbitrary number of pulses is directly expressed in terms of the uncontrolled decoherence function. In particular, analytical expressions are obtained for approximation of the long- and short-term coherence behavior for both Ohmic and supra-Ohmic environments. By focusing on the realistic case of pure dephasing in an excitonic qubit, we quantitatively assess the impact of physical constraints on achievable pulse separations, and show that little advantage of high-level decoupling schemes based on concatenated or optimal design may be expected if pulses cannot be applied sufficiently fast. In such constrained scenarios, we demonstrate how simple modifications of repeated periodic-echo protocols can offer significantly improved coherence preservation in realistic parameter regimes. We expect similar conclusions to be relevant to other constrained qubit devices exposed to quantum or classical phase noise.
DEFF Research Database (Denmark)
Langbein, Wolfgang Werner; Hvam, Jørn Märcher; Zimmermann, R.
1999-01-01
). This method determines the decays of intensity and coherence separately, thus distinguishing lifetime from pure dephasing. The secondary emission of excitons in semiconductor quantum wells is investigated. Here the combination of static disorder and inelastic scattering leads to a partially coherent emission....... The temperature dependence is well explained by phonon scattering....
Directory of Open Access Journals (Sweden)
Daniel Makina
2016-09-01
Full Text Available In the literature, positive investment cash flow sensitivity is attributed to either asymmetric information induced financing constraints or the agency costs of free cash flow. Using data from a sample of 68 manufacturing firms listed on the South African JSE, this paper contributes to the literature by investigating the source of investment cash flow sensitivity. We have found that asymmetric information explains the positive investment cash flow sensitivity better than agency costs. Furthermore, asymmetric information has been observed to be more pronounced in low-dividend-paying firms and small firms. Despite South Africa’s having a developed financial system by international standards, small firms are seen to be financially constrained. We attribute the absence of investment cash flow sensitivity due to agency costs to good corporate governance of South African listed firms. Thus the paper provides further evidence in support of the proposition in the literature that the source of investment cash flow sensitivity may depend on the institutional setting of a country, such as its corporate governance.
Dephasing of LO-phonon-plasmon hybrid modes in n-type GaAs
Vallée, F.; Ganikhanov, F.; Bogani, F.
1997-11-01
The relaxation dynamics of coherent phononlike LO-phonon-plasmon hybrid modes is investigated in n-doped GaAs using an infrared time-resolved coherent anti-Stokes Raman scattering technique. Measurements performed for different crystal temperatures in the range 10-300 K as a function of the electron density injected by doping show a large reduction of the hybrid mode dephasing time compared to the bare LO-phonon one for densities larger than 1016 cm-3. The results are interpreted in terms of coherent decay of the LO-phonon-plasmon mixed mode in the weak-coupling regime and yield information on the plasmon and electron relaxation. The estimated average electron momentum relaxation times are smaller than those deduced from Hall mobility measurements, as expected from our theoretical model.
Interactions, Disorder and Dephasing in Superconducting Films and Quantum Hall Systems
International Nuclear Information System (INIS)
Auerbach, A.
1999-01-01
It is shown that a large class of two dimensional Superconductor to Insulator (SC-I), and (Quantum Hall to Insulator (QH-I) transitions can be understood by assuming that the thermodynamic transition in the clean system is first order. The finite correlation lengths at that transition yield a natural separation of the disorder into short and long wavelengths which are then straightforward to incorporate perturbatively and semi classically respectively. This approach reduces problems of disorder+interactions to puddle network models, whose studies have already yielded insight into experiments of QH-I and SC-I. For the CQH-I, the difference between Landauer-Buttiker and Boltzman theories highlights effects of dephasing
Dephasing due to Nuclear Spins in Large-Amplitude Electric Dipole Spin Resonance.
Chesi, Stefano; Yang, Li-Ping; Loss, Daniel
2016-02-12
We analyze effects of the hyperfine interaction on electric dipole spin resonance when the amplitude of the quantum-dot motion becomes comparable or larger than the quantum dot's size. Away from the well-known small-drive regime, the important role played by transverse nuclear fluctuations leads to a Gaussian decay with characteristic dependence on drive strength and detuning. A characterization of spin-flip gate fidelity, in the presence of such additional drive-dependent dephasing, shows that vanishingly small errors can still be achieved at sufficiently large amplitudes. Based on our theory, we analyze recent electric dipole spin resonance experiments relying on spin-orbit interactions or the slanting field of a micromagnet. We find that such experiments are already in a regime with significant effects of transverse nuclear fluctuations and the form of decay of the Rabi oscillations can be reproduced well by our theory.
Role of energy exchange in vibrational dephasing processes in liquids and solids
International Nuclear Information System (INIS)
Marks, S.
1981-08-01
Three theories which claim relevance to the dephasing of molecular vibrations in condensed phase matter are presented. All of these theories predict (in certain limiting cases) that the widths and shifts of molecular vibrations will obey an Arrhenius temperature dependence. The basic tenets of the theories are detailed so that the differences between them may be used in an experiment to distinguish between them. One model, based on intermolecular energy exchange of low-frequency modes, results in dephasing the high-frequency modes when anharmonic coupling is present. A computer analysis of temperature dependent experimental lineshapes can result in the extraction of various parameters such as the anharmonic shifts and the exchange rates. It is shown that, in order to properly assess the relative validity of the three models, other evidence must be obtained such as the spectral parameters of the low-frequency modes, the combination bands, and the isotopic dilution behavior. This evidence is presented for d 14 -durene (perdeutero-1,2,4,5-tetramethylbenzene) and compared to previous data obtained on pure h 14 -durene. An extension of the (HSC) intermolecular energy exchange model which allows for the possibility of partial delocalization of the low-frequency modes gives an adequate description of the experimental evidence. Isotopic dilution experiments, in particular, have resulted in a detailed picture of the energy transfer dynamics of the low-frequency modes. A section in which some spontaneous Raman spectra support a model of inhomogeneous broadening in liquids based on results of picosecond stimulated Raman spectroscopy is presented. The model is that a distribution of environmental sites is created by a distribution in the local density and thus creates inhomogeneous broadening
International Nuclear Information System (INIS)
Marks, S.; Cornelius, P.A.; Harris, C.B.
1980-01-01
A series of experiments have been conducted in order to evaluate the relative importance of several recent theories of vibrational dephasing in solids. The theories are discussed briefly, and are used to interpret the temperature dependence of the C--H and C--D stretch bands in the spontaneous Raman spectra of h 14 - and d 14 -1,2,4,5-tetramethyl benzene (durene). The infrared spectra of these same molecules are also reported in the region of the combination bands involving C--H (or C--D) stretches and low-frequency modes. The results support the applicability of the model of Harris et al., [C. B. Harris, R. M. Shelby and P. A. Cornelius, Phys. Rev. Lett. 38, 1415 (1977); Chem Phys. Lett. 57, 8 (1978); R. M. Shelby, C. B. Harris, and P. A. Cornelius, J. Chem. Phys. 70, 34 (1979)], based on energy exchange in anharmonically coupled low-frequency modes. This theory is then used, in connection with Raman spectra obtained in isotopically mixed samples of durene, to elucidate the vibrational dynamics underlying the dephasing. It is found that the results are consistent with the hypothesis that some low-frequency modes in this molecule are significantly delocalized or ''excitonic'' in character, and that this delocalization may be studied by means of Raman spectroscopy on the low-frequency modes themselves, as well as by exchange analysis of the coupled high-frequency modes. These conclusions represent a generalization and extension of the previously published exchange model [R. M. Shelby, C. B. Harris, and P. A. Cornelius, J. Chem Phys. 70, 34 (1979)
George, R.; Kabir, M.R.; Qian, J.
2005-01-01
Several studies use the investment - cash flow sensitivity as a measure of financing constraints while some others disagree.The source of this disparity lies mostly in differences in opinion regarding the segregation of severely financially constrained firms from less constrained ones.We examine
Joo, Taiha; Albrecht, A. C.
1993-06-01
Time-resolved degenerate four-wave mixing (TRDFWM) for an electronically resonant system in a phase-matching configuration that measures population decay is reported. Because the spectral width of input light exceeds the vibrational Bohr frequency of a strong Raman active mode, the vibrational coherence produces strong oscillations in the TRDFWM signal together with the usual population decay from the excited electronic state. The data are analyzed in terms of a four-level system: ground and excited electronic states each split by a vibrational quantum of a Raman active mode. Absolute frequencies and their dephasing times of the vibrational modes at ≈590 cm -1 are obtained for the excited as well as the ground electronic state. The vibrational dephasing rate in the excited electronic state is about an order of magnitude faster than that in the ground state, the origin of which is speculated upon.
International Nuclear Information System (INIS)
Stanton, C.J.; Kenrow, J.; El Sayed, K.; Jho, Y.D.; Kim, D.S.; Song, J.J.; Fischer, Arthur Joseph
2004-01-01
Femtosecond differential reflectivity spectroscopy (DRS) and four-wave mixing (FWM) experiments were performed simultaneously to study the initial temporal dynamics of the exciton line-shapes in GaN epilayers. Beats between the A-B excitons were found only for positive time delay in both DRS and FWM experiments. The rise time at negative time delay for the DRS was much slower than the FWM signal or differential transmission spectroscopy at the exciton resonance. A numerical solution of a six band semiconductor Bloch equation model including nonlinearities at the Hartree-Fock level shows that this slow rise in the DRS results from excitation induced dephasing, that is, the strong density dependence of the dephasing time which changes with the laser excitation energy.
Acoustic phonon dephasing in shallow GaAs/Ga 1- xAl xAs single quantum wells
Cassabois, G.; Meccherini, S.; Roussignol, Ph.; Bogani, F.; Gurioli, M.; Colocci, M.; Planel, R.; Thierry-Mieg, V.
1998-07-01
The intermediate dimensionality regime is studied on a set of shallow GaAs/Ga 1- xAl xAs single quantum wells. Such heterostructures exhibit 2D strong excitonic electroabsorption together with near 3D fast transport properties. We report dephasing time measurements ( T2) of the heavy-hole exciton and we show that the acoustic phonon contribution decreases with x to a value in good agreement with theoretical predictions for GaAs bulk.
Choo, Kenny; Bissbort, Ulf; Poletti, Dario
2017-01-01
We study the response of a particle current to dissipative dephasing in an interacting, few-body fermionic lattice system. The particles are prepared in the ground state in presence of an artificial magnetic gauge field, which is subsequently quenched to zero. The initial current decays non-trivially in the dissipative environment and we explore the emerging dynamics and its dependence on various system parameters.
Song, Ya-Ju; Tan, Qing-Shou; Kuang, Le-Man
2017-03-08
We investigate the possibility to control quantum evolution speed of a single dephasing qubit for arbitrary initial states by the use of periodic dynamical decoupling (PDD) pulses. It is indicated that the quantum speed limit time (QSLT) is determined by initial and final quantum coherence of the qubit, as well as the non-Markovianity of the system under consideration during the evolution when the qubit is subjected to a zero-temperature Ohmic-like dephasing reservoir. It is shown that final quantum coherence of the qubit and the non-Markovianity of the system can be modulated by PDD pulses. Our results show that for arbitrary initial states of the dephasing qubit with non-vanishing quantum coherence, PDD pulses can be used to induce potential acceleration of the quantum evolution in the short-time regime, while PDD pulses can lead to potential speedup and slow down in the long-time regime. We demonstrate that the effect of PDD on the QSLT for the Ohmic or sub-Ohmic spectrum (Markovian reservoir) is much different from that for the super-Ohmic spectrum (non-Markovian reservoir).
International Nuclear Information System (INIS)
Geddes, C.G.R.; Toth, Cs.; Tilborg, J. van; Esarey, E.; Schroeder, C.B.; Bruhwiler, D.; Nieter, C.; Cary, J.; Leemans, W.P.
2005-01-01
High-quality electron beams, with a few 10 9 electrons within a few percent of the same energy above 80 MeV, were produced in a laser wakefield accelerator by matching the acceleration length to the length over which electrons were accelerated and outran (dephased from) the wake. A plasma channel guided the drive laser over long distances, resulting in production of the high-energy, high-quality beams. Unchanneled experiments varying the length of the target plasma indicated that the high-quality bunches are produced near the dephasing length and demonstrated that channel guiding was more stable and efficient than relativistic self-guiding. Consistent with these data, particle-in-cell simulations indicate production of high-quality electron beams when trapping of an initial bunch of electrons suppresses further injection by loading the wake. The injected electron bunch is then compressed in energy by dephasing, when the front of the bunch begins to decelerate while the tail is still accelerated
Lawless, Mary K.; Mathies, Richard A.
1992-06-01
Absolute resonance Raman cross sections are measured for Nile blue 690 perchlorate dissolved in ethylene glycol with excitation at 514, 531, and 568 nm. These values and the absorption spectrum are modeled using a time-dependent wave packet formalism. The excited-state equilibrium geometry changes are quantitated for 40 resonance Raman active modes, seven of which (590, 1141, 1351, 1429, 1492, 1544, and 1640 cm-1 ) carry 70% of the total resonance Raman intensity. This demonstrates that in addition to the prominent 590 and 1640 cm-1 modes, a large number of vibrational degrees of freedom are Franck-Condon coupled to the electronic transition. After exposure of the explicit vibrational progressions, the residual absorption linewidth is separated into its homogeneous [350 cm-1 half-width at half-maximum (HWHM)] and inhomogeneous (313 cm-1 HWHM) components through an analysis of the absolute Raman cross sections. The value of the electronic dephasing time derived from this study (25 fs) compares well to previously published results. These data should be valuable in multimode modeling of femtosecond experiments on Nile blue.
Dynamics of electronic dephasing in the Fenna-Matthews-Olson complex
International Nuclear Information System (INIS)
Hayes, Dugan; Panitchayangkoon, Gitt; Fransted, Kelly A; Caram, Justin R; Freed, Karl F; Engel, Gregory S; Wen Jianzhong
2010-01-01
Electronic coherence has been shown to persist in the Fenna-Matthews-Olson (FMO) antenna complex from green sulfur bacteria at 77 K for at least 660 fs, several times longer than the typical lifetime of a coherence in a dynamic environment at this temperature. Such long-lived coherence was proposed to improve energy transfer efficiency in photosynthetic systems by allowing an excitation to follow a quantum random walk as it approaches the reaction centre. Here we present a model for bath-induced electronic transitions, demonstrating that the protein matrix protects coherences by globally correlating fluctuations in transition energies. We also quantify the dephasing rates for two particular electronic coherences in the FMO complex at 77 K using two-dimensional Fourier transform electronic spectroscopy and find that the lifetimes of individual coherences are distinct. Within the framework of noise-assisted transport, this result suggests that the FMO complex has been locally tuned by natural selection to optimize transfer efficiency by exploiting quantum coherence.
Orbital hyperfine interaction and qubit dephasing in carbon nanotube quantum dots
Palyi, Andras; Csiszar, Gabor
2015-03-01
Hyperfine interaction (HF) is of key importance for the functionality of solid-state quantum information processing, as it affects qubit coherence and enables nuclear-spin quantum memories. In this work, we complete the theory of the basic hyperfine interaction mechanisms (Fermi contact, dipolar, orbital) in carbon nanotube quantum dots by providing a theoretical description of the orbital HF. We find that orbital HF induces an interaction between the nuclear spins of the nanotube lattice and the valley degree of freedom of the electrons confined in the quantum dot. We show that the resulting nuclear-spin-electron-valley interaction (i) is approximately of Ising type, (ii) is essentially local, in the sense that an effective atomic interaction strength can be defined, and (iii) has a strength that is comparable to the combined strength of Fermi contact and dipolar interactions. We argue that orbital HF provides a new decoherence mechanism for single-electron valley qubits and spin-valley qubits in a range of multi-valley materials. We explicitly evaluate the corresponding inhomogeneous dephasing time T2* for a nanotube-based valley qubit. We acknowledge funding from the EU Marie Curie CIG-293834, OTKA Grant PD 100373, and EU ERC Starting Grant CooPairEnt 258789. AP is supported by the Janos Bolyai Scholarship of the Hungarian Academy of Sciences.
Guo, Wenzhang; Wang, Hao; Wu, Zhengping
2018-03-01
Most existing cascading failure mitigation strategy of power grids based on complex network ignores the impact of electrical characteristics on dynamic performance. In this paper, the robustness of the power grid under a power decentralization strategy is analysed through cascading failure simulation based on AC flow theory. The flow-sensitive (FS) centrality is introduced by integrating topological features and electrical properties to help determine the siting of the generation nodes. The simulation results of the IEEE-bus systems show that the flow-sensitive centrality method is a more stable and accurate approach and can enhance the robustness of the network remarkably. Through the study of the optimal flow-sensitive centrality selection for different networks, we find that the robustness of the network with obvious small-world effect depends more on contribution of the generation nodes detected by community structure, otherwise, contribution of the generation nodes with important influence on power flow is more critical. In addition, community structure plays a significant role in balancing the power flow distribution and further slowing the propagation of failures. These results are useful in power grid planning and cascading failure prevention.
Equivalence principle for quantum systems: dephasing and phase shift of free-falling particles
Anastopoulos, C.; Hu, B. L.
2018-02-01
We ask the question of how the (weak) equivalence principle established in classical gravitational physics should be reformulated and interpreted for massive quantum objects that may also have internal degrees of freedom (dof). This inquiry is necessary because even elementary concepts like a classical trajectory are not well defined in quantum physics—trajectories originating from quantum histories become viable entities only under stringent decoherence conditions. From this investigation we posit two logically and operationally distinct statements of the equivalence principle for quantum systems. Version A: the probability distribution of position for a free-falling particle is the same as the probability distribution of a free particle, modulo a mass-independent shift of its mean. Version B: any two particles with the same velocity wave-function behave identically in free fall, irrespective of their masses. Both statements apply to all quantum states, including those without a classical correspondence, and also for composite particles with quantum internal dof. We also investigate the consequences of the interaction between internal and external dof induced by free fall. For a class of initial states, we find dephasing occurs for the translational dof, namely, the suppression of the off-diagonal terms of the density matrix, in the position basis. We also find a gravitational phase shift in the reduced density matrix of the internal dof that does not depend on the particle’s mass. For classical states, the phase shift has a natural classical interpretation in terms of gravitational red-shift and special relativistic time-dilation.
International Nuclear Information System (INIS)
Goan, Hsi-Sheng; Jian, Chung-Chin; Chen, Po-Wen
2010-01-01
We evaluate the non-Markovian finite-temperature two-time correlation functions (CF's) of system operators of a pure-dephasing spin-boson model in two different ways, one by the direct exact operator technique and the other by the recently derived evolution equations, valid to second order in the system-environment interaction Hamiltonian. This pure-dephasing spin-boson model that is exactly solvable has been extensively studied as a simple decoherence model. However, its exact non-Markovian finite-temperature two-time system operator CF's, to our knowledge, have not been presented in the literature. This may be mainly due to the fact, illustrated in this article, that in contrast to the Markovian case, the time evolution of the reduced density matrix of the system (or the reduced quantum master equation) alone is not sufficient to calculate the two-time system operator CF's of non-Markovian open systems. The two-time CF's obtained using the recently derived evolution equations in the weak system-environment coupling case for this non-Markovian pure-dephasing model happen to be the same as those obtained from the exact evaluation. However, these results significantly differ from the non-Markovian two-time CF's obtained by wrongly directly applying the quantum regression theorem (QRT), a useful procedure to calculate the two-time CF's for weak-coupling Markovian open systems. This demonstrates clearly that the recently derived evolution equations generalize correctly the QRT to non-Markovian finite-temperature cases. It is believed that these evolution equations will have applications in many different branches of physics.
Observation of the in-plane spin-dephasing anisotropy in [111]-grown GaAs/AlGaAs quantum well
International Nuclear Information System (INIS)
Zhao, Chunbo; Li, Junbin; Yu, Ying; Ni, Haiqiao; Niu, Zhichuan; Zhang, Xinhui
2014-01-01
The electron density and temperature dependent in-plane spin-dephasing anisotropy in [111]-grown GaAs quantum well (QW) has been investigated by time-resolved magneto-Kerr rotation technique. Due to the specific symmetry of [111]-grown quantum well, the in-plane Rashba and linear Dresselhaus effective spin-orbit magnetic field is parallel to each other for electron wave vectors in all directions. However, an obvious in-plane spin-dephasing anisotropy comparing [2 ¯ 11] with [01 ¯ 1] crystalline orientations has been observed and discussed in this work. Our results demonstrate the innegligible spin dephasing channel through inhomogeneous broadening induced by the out-of-plane non-linear Dresselhaus field, which arises naturally from the C 3 symmetry of [111]-grown GaAs QW
International Nuclear Information System (INIS)
Cosottini, M.; Calabrese, R.; Murri, L.; Puglioli, M.; Zampa, V.; Michelassi, M.C.; Ortori, S.; Bartolozzi, C.
2003-01-01
The aim of this study was to evaluate diagnostic accuracy of contrast-enhanced MRA (CEMRA) compared with digital subtraction angiography (DSA) in studying neck vessels of 48 patients. In three groups of patients, we used three MRA protocols differing for voxel size to assess if intravoxel dephasing effects could modify accuracy of CEMRA. Accuracy and correlation with DSA results were calculated in all patients and separately in the three groups. A qualitative analysis of the likeness between morphology of the stenosis in CEMRA and DSA images was also assessed. In all patients accuracy and agreement with DSA were 96% and k=0.85 in subclavian arteries, 96% and k=0.84 in vertebral artery, 97% and k=0.88 in common carotid arteries, and 94% and k=0.86 in internal carotid arteries. In the three groups accuracy and agreement with DSA did not show any significant difference. Qualitative analysis of CEMRA and DSA images revealed a better agreement in depicting the morphology of stenosis using a smaller voxel size. The CEMRA represents a powerful tool for the non-invasive evaluation of neck vessels. Overestimation trend of CEMRA is confirmed and the reduction of voxel size, decreasing the dephasing intravoxel effect, allows to have a better overlapping of stenosis morphology on CEMRA compared with DSA, but it does not yield diagnostic gain in the stenosis grading. (orig.)
Roy, Chiranjeeb; John, Sajeev
2010-02-01
We derive a quantum theory of the role of acoustic and optical phonons in modifying the optical absorption line shape, polarization dynamics, and population dynamics of a two-level atom (quantum dot) in the “colored” electromagnetic vacuum of a photonic band-gap (PBG) material. This is based on a microscopic Hamiltonian describing both radiative and vibrational processes quantum mechanically. We elucidate the extent to which phonon-assisted decay limits the lifetime of a single photon-atom bound state and derive the modified spontaneous emission dynamics due to coupling to various phonon baths. We demonstrate that coherent interaction with undamped phonons can lead to an enhanced lifetime of a photon-atom bound state in a PBG. This results in reduction of the steady-state atomic polarization but an increase in the fractionalized upper state population in the photon-atom bound state. We demonstrate, on the other hand, that the lifetime of the photon-atom bound state in a PBG is limited by the lifetime of phonons due to lattice anharmonicities (breakup of phonons into lower energy phonons) and purely nonradiative decay. We also derive the modified polarization decay and dephasing rates in the presence of such damping. This leads to a microscopic, quantum theory of the optical absorption line shapes. Our model and formalism provide a starting point for describing dephasing and relaxation in the presence of external coherent fields and multiple quantum dot interactions in electromagnetic reservoirs with radiative memory effects.
International Nuclear Information System (INIS)
Roy, Chiranjeeb; John, Sajeev
2010-01-01
We derive a quantum theory of the role of acoustic and optical phonons in modifying the optical absorption line shape, polarization dynamics, and population dynamics of a two-level atom (quantum dot) in the ''colored'' electromagnetic vacuum of a photonic band-gap (PBG) material. This is based on a microscopic Hamiltonian describing both radiative and vibrational processes quantum mechanically. We elucidate the extent to which phonon-assisted decay limits the lifetime of a single photon-atom bound state and derive the modified spontaneous emission dynamics due to coupling to various phonon baths. We demonstrate that coherent interaction with undamped phonons can lead to an enhanced lifetime of a photon-atom bound state in a PBG. This results in reduction of the steady-state atomic polarization but an increase in the fractionalized upper state population in the photon-atom bound state. We demonstrate, on the other hand, that the lifetime of the photon-atom bound state in a PBG is limited by the lifetime of phonons due to lattice anharmonicities (breakup of phonons into lower energy phonons) and purely nonradiative decay. We also derive the modified polarization decay and dephasing rates in the presence of such damping. This leads to a microscopic, quantum theory of the optical absorption line shapes. Our model and formalism provide a starting point for describing dephasing and relaxation in the presence of external coherent fields and multiple quantum dot interactions in electromagnetic reservoirs with radiative memory effects.
DEFF Research Database (Denmark)
Wagner, Hans Peter; Schätz, A.; Maier, R.
1998-01-01
We investigate the interaction and dephasing of the excitons in wide ZnSe/Zn0.94Mg0.06Se quantum wells by spectrally resolved, femtosecond four-wave mixing (FWM). Polarization-dependent measurements indicate that excitation-induced dephasing is the dominant FWM process. The biexcitons of the center...... repulsion for coherent excitons. The exciton interaction rates with acoustic and optical phonons are deduced by their temperature dependencies. The acoustic-phonon scattering is found to be strongly reduced in the investigated wide wells due to the reduced accessible phonon wave vector....
Directory of Open Access Journals (Sweden)
Alan Nader Ackel Ghani
2015-04-01
Full Text Available This article analyzes the credit constraints, using the cash flow sensitivity approach, of private and listed companies between 2007 and 2010. According to this approach, the econometric results show that the credit constraints are the same for either private or listed companies. This paper seeks to contribute to the literature because the study of credit constraints of private companies based on cash flow sensitivity in Brazil has been rare.
Denega, S.Z.; Last, Thorsten; Liu, J.; Slachter, A.; Rizo, P.J.; Loosdrecht, P.H.M. van; Wees, B.J. van; Reuter, D.; Wieck, A.D.; Wal, C.H. van der
2010-01-01
We report a study of suppressed spin dephasing for quasi-one-dimensional electron ensembles in wires etched into a GaAs/AlGaAs heterojunction system. Time-resolved Kerr-rotation measurements show a suppression that is most pronounced for wires along the [110] crystal direction. This is the
The effect of dephasing on edge state transport through p-n junctions in HgTe/CdTe quantum wells.
Zhang, Ying-Tao; Song, Juntao; Sun, Qing-Feng
2014-02-26
Using the Landauer-Büttiker formula, we study the effect of dephasing on the transport properties of the HgTe/CdTe p-n junction. It is found that in the HgTe/CdTe p-n junction the topologically protected gapless helical edge states manifest a quantized 2e²/h plateau robust against dephasing, in sharp contrast to the case for the normal HgTe/CdTe quantum well. This robustness of the transport properties of the edge states against dephasing should be attributed to the special construction of the HgTe/CdTe p-n junction, which limits the gapless helical edge states to a very narrow region and thus weakens the influence of the dephasing on the gapless edge states to a large extent. Our results demonstrate that the p-n junction could be a substitute device for use in experimentally observing the robust edge states and quantized plateau. Finally, we present a feasible scheme based on current experimental methods.
Roszak, Katarzyna; Cywiński, Łukasz
2018-01-01
We find that when a qubit initialized in a pure state experiences pure dephasing due to interaction with an environment, separable qubit-environment states generated during the evolution also have zero quantum discord with respect to the environment. What follows is that the set of separable states which can be reached during the evolution has zero volume, and hence, such effects as sudden death of qubit-environment entanglement are very unlikely. In the case of the discord with respect to the qubit, a vast majority of qubit-environment separable states is discordant, but in specific situations zero-discord states are possible. This is conceptually important since there is a connection between the discordance with respect to a given subsystem and the possibility of describing the evolution of this subsystem using completely positive maps. Finally, we use the formalism to find an exemplary evolution of an entangled state of two qubits that is completely positive, and occurs solely due to interaction of only one of the qubits with its environment (so one could guess that it corresponds to a local operation, since it is local in a physical sense), but which nevertheless causes the enhancement of entanglement between the qubits. While this simply means that the considered evolution is completely positive, but does not belong to local operations and classical communication, it shows how much caution has to be exercised when identifying evolution channels that belong to that class.
Sulc, Miroslav; Hernandez, Henar; Martinez, Todd J.; Vanicek, Jiri
2014-03-01
We recently showed that the Dephasing Representation (DR) provides an efficient tool for computing ultrafast electronic spectra and that cellularization yields further acceleration [M. Šulc and J. Vaníček, Mol. Phys. 110, 945 (2012)]. Here we focus on increasing its accuracy by first implementing an exact Gaussian basis method (GBM) combining the accuracy of quantum dynamics and efficiency of classical dynamics. The DR is then derived together with ten other methods for computing time-resolved spectra with intermediate accuracy and efficiency. These include the Gaussian DR (GDR), an exact generalization of the DR, in which trajectories are replaced by communicating frozen Gaussians evolving classically with an average Hamiltonian. The methods are tested numerically on time correlation functions and time-resolved stimulated emission spectra in the harmonic potential, pyrazine S0 /S1 model, and quartic oscillator. Both the GBM and the GDR are shown to increase the accuracy of the DR. Surprisingly, in chaotic systems the GDR can outperform the presumably more accurate GBM, in which the two bases evolve separately. This research was supported by the Swiss NSF Grant No. 200021_124936/1 and NCCR Molecular Ultrafast Science & Technology (MUST), and by the EPFL.
Ozgur Arslan; Chrisostomos Florackis; Aydin Ozkan
2006-01-01
This paper investigates the relationship between financing constraints and investment-cash flow sensitivities by focusing on cash holdings of firms as the basic classification scheme to separate firms into financially constrained and unconstrained categories. The idea is that high cash reserves increase the ability of firms to undertake profitable investment opportunities. Our classification scheme is based on an optimal cash model, which helps us identify the firms that deviate significantly...
Binding energy and dephasing of biexcitons in In0.18Ga0.82As/GaAs single quantum wells
DEFF Research Database (Denmark)
Borri, Paola; Langbein, Wolfgang Werner; Hvam, Jørn Märcher
1999-01-01
Biexciton binding energies and biexciton dephasing in In0.18Ga0.82As/GaAs single quantum wells have been measured by time-integrated and spectrally resolved four-wave mixing. The biexciton binding energy increases from 1.5 to 2.6 meV for well widths increasing from 1 to 4 nm. The ratio between...... exciton and biexciton binding energy changes from 0.23 to 0.3 with increasing inhomogeneous broadening, corresponding to increasing well width. From the temperature dependence of the exciton and biexciton four-wave mixing signal decay, we have deduced the acoustic-phonon scattering of the exciton...
Shamim, Saquib; Mahapatra, S; Scappucci, G; Klesse, W M; Simmons, M Y; Ghosh, Arindam
2017-05-04
We report quantum transport measurements on two dimensional (2D) Si:P and Ge:P δ-layers and compare the inelastic scattering rates relevant for weak localization (WL) and universal conductance fluctuations (UCF) for devices of various doping densities (0.3-2.5 × 10 18 m -2 ) at low temperatures (0.3-4.2 K). The phase breaking rate extracted experimentally from measurements of WL correction to conductivity and UCF agree well with each other within the entire temperature range. This establishes that WL and UCF, being the outcome of quantum interference phenomena, are governed by the same dephasing rate.
Gallart, M.; Ziegler, M.; Crégut, O.; Feltin, E.; Carlin, J.-F.; Butté, R.; Grandjean, N.; Hönerlage, B.; Gilliot, P.
2017-07-01
Applying four-wave mixing spectroscopy to a high-quality GaN/AlGaN single quantum well, we report on the experimental determination of excitonic dephasing times at different temperatures and exciton densities in III-nitride heterostructures. By comparing the evolution with the temperature of the dephasing and the spin-relaxation rate, we conclude that both processes are related to the rate of excitonic collisions. When spin relaxation occurs in the motional-narrowing regime, it remains constant over a large temperature range as the spin-precession frequency increases linearly with temperature, hence compensating for the observed decrease in the dephasing time. From those measurements, a value of the electron-hole exchange interaction strength of 0.45 meV at T =10 K is inferred.
International Nuclear Information System (INIS)
Togami, Izumi; Sasai, Nobuya; Tsunoda, Masatoshi; Sei, Tetsurou; Sato, Shuhei; Yabuki, Takayuki; Hiraki, Yoshio
2002-01-01
The FAIR-HASTE method is a kind of noninvasive perfusion MR imaging obtained without the use of contrast media. By subtracting a flow-insensitive image from a flow-sensitive image, contrast enhancement of inflowing blood achieved. In the present study, we applied pulmonary perfusion FAIR-HASTE sequence for 23 patients with various pulmonary diseases, and compared the findings with those by pulmonary perfusion scintigraphy and Gadolinium perfusion MRI. Pulmonary perfusion imaging with the FAIR-HASTE method was possible in all clinical cases, and the findings corresponded well to those obtained by perfusion MRI using contrast media or pulmonary scintigraphy. The FAIR-HASTE method is a promising method for the evaluation of pulmonary perfusion. (author)
International Nuclear Information System (INIS)
Yamashita, Eijiro; Kanasaki, Yoshiko; Fujii, Shinya; Ogawa, Toshihide; Tanaka, Takuro; Hirata, Yoshiharu
2011-01-01
Background Increased venous contrast in ischemic stroke using susceptibility-weighted imaging has been widely reported, although few reports have compared increased venous contrast areas with perfusion change areas. Purpose To compare venous contrast on phase-sensitive MR images (PSI) with perfusion change on flow-sensitive alternating inversion recovery (FAIR) images, and to discuss the clinical use of PSI in ischemic stroke. Material and Methods Thirty patients with clinically suspected acute infarction of the middle cerebral artery (MCA) territory within 7 days of onset were evaluated. Phase-sensitive imaging (PSI), flow-sensitive alternating inversion recovery (FAIR), diffusion-weighted imaging (DWI) and magnetic resonance angiography (MRA) were obtained using 3 Tesla scanner. Two neuroradiologists independently reviewed the MR images, as well as the PSI, DWI, and FAIR images. They were blinded to the clinical data and to each other's findings. The abnormal area of each image was ultimately identified after both neuroradiologists reached consensus. We analyzed areas of increased venous contrast on PSI, perfusion changes on FAIR images and signal changes on DWI for each case. Results Venous contrast increased on PSI and hypoperfusion was evident on FAIR images from 22 of the 30 patients (73%). The distribution of the increased venous contrast was the same as that of the hypoperfused areas on FAIR images in 16 of these 22. The extent of these lesions was larger than that of lesions visualized by on DWI in 18 of the 22 patients. Hypointense signals reflecting hemorrhage and no increased venous contrast on PSI and hyperperfusion on FAIR images were found in six of the remaining eight patients (20%). Findings on PSI were normal and hypoperfusion areas were absent on FAIR images of two patients (7%). Conclusion Increased venous contrast on PSI might serve as an index of misery perfusion and provide useful information
Hirtler, Daniel; Garcia, Julio; Barker, Alex J; Geiger, Julia
2016-10-01
To comprehensively and quantitatively analyse flow and vorticity in the right heart of patients after repair of tetralogy of Fallot (rTOF) compared with healthy volunteers. Time-resolved flow-sensitive 4D MRI was acquired in 24 rTOF patients and 12 volunteers. Qualitative flow evaluation was based on consensus reading of two observers. Quantitative analysis included segmentation of the right atrium (RA) and ventricle (RV) in a four-chamber view to extract volumes and regional haemodynamic information for computation of regional mean and peak vorticity. Right heart intra-atrial, intraventricular and outflow tract flow patterns differed considerably between rTOF patients and volunteers. Peak RA and mean RV vorticity was significantly higher in patients (p = 0.02/0.05). Significant negative correlations were found between patients' maximum and mean RV and RA vorticity and ventricular volumes (p tetralogy of Fallot. • Regurgitant flow in the main pulmonary artery is associated with higher right heart vorticity.
Energy Technology Data Exchange (ETDEWEB)
Hirtler, Daniel [University Hospital Freiburg, Department of Congenital Heart Defects and Pediatric Cardiology (Heart Center, University of Freiburg), Freiburg (Germany); Garcia, Julio; Barker, Alex J. [Northwestern University Feinberg School of Medicine, Department of Radiology, Chicago, IL (United States); Geiger, Julia [University Childrens' Hospital Zurich, Department of Radiology, Zurich (Switzerland)
2016-10-15
To comprehensively and quantitatively analyse flow and vorticity in the right heart of patients after repair of tetralogy of Fallot (rTOF) compared with healthy volunteers. Time-resolved flow-sensitive 4D MRI was acquired in 24 rTOF patients and 12 volunteers. Qualitative flow evaluation was based on consensus reading of two observers. Quantitative analysis included segmentation of the right atrium (RA) and ventricle (RV) in a four-chamber view to extract volumes and regional haemodynamic information for computation of regional mean and peak vorticity. Right heart intra-atrial, intraventricular and outflow tract flow patterns differed considerably between rTOF patients and volunteers. Peak RA and mean RV vorticity was significantly higher in patients (p = 0.02/0.05). Significant negative correlations were found between patients' maximum and mean RV and RA vorticity and ventricular volumes (p < 0.05). The main pulmonary artery (MPA) regurgitant flow was associated with higher RA and RV vorticity, which was significant for RA maximum and RV mean vorticity (p = 0.01/0.03). The calculation of vorticity based on 4D flow data is an alternative approach to assess intracardiac flow changes in rTOF patients compared with qualitative flow visualization. Alterations in intracardiac vorticity could be relevant with regard to the development of RV dilation and impaired function. (orig.)
International Nuclear Information System (INIS)
Hirtler, Daniel; Garcia, Julio; Barker, Alex J.; Geiger, Julia
2016-01-01
To comprehensively and quantitatively analyse flow and vorticity in the right heart of patients after repair of tetralogy of Fallot (rTOF) compared with healthy volunteers. Time-resolved flow-sensitive 4D MRI was acquired in 24 rTOF patients and 12 volunteers. Qualitative flow evaluation was based on consensus reading of two observers. Quantitative analysis included segmentation of the right atrium (RA) and ventricle (RV) in a four-chamber view to extract volumes and regional haemodynamic information for computation of regional mean and peak vorticity. Right heart intra-atrial, intraventricular and outflow tract flow patterns differed considerably between rTOF patients and volunteers. Peak RA and mean RV vorticity was significantly higher in patients (p = 0.02/0.05). Significant negative correlations were found between patients' maximum and mean RV and RA vorticity and ventricular volumes (p < 0.05). The main pulmonary artery (MPA) regurgitant flow was associated with higher RA and RV vorticity, which was significant for RA maximum and RV mean vorticity (p = 0.01/0.03). The calculation of vorticity based on 4D flow data is an alternative approach to assess intracardiac flow changes in rTOF patients compared with qualitative flow visualization. Alterations in intracardiac vorticity could be relevant with regard to the development of RV dilation and impaired function. (orig.)
Sadat Hashemi, Somayeh; Ghavami Sabouri, Saeed; Khorsandi, Alireza
2018-04-01
We present a theoretical model in order to study the effect of a thermally loaded crystal on the quality of a second-harmonic (SH) beam generated in a high-power pumping regime. The model is provided based on using a particular structure of oven considered for MgO:PPsLT nonlinear crystal to compensate for the thermal de-phasing effect that as the pumping power reaches up to 50 W degrades the conversion efficiency and beam quality of the interacting beams. Hereupon, the quality of fundamental beam is involved in the modeling to investigate the final effect on the beam quality of generated SH beam. Beam quality evaluation is subsequently simulated using Hermite-Gaussian modal decomposition approach for a range of fundamental beam qualities varied from 1 to 3 and for different levels of input powers. To provide a meaningful comparison numerical simulation is correlated with real data deduced from a high-power SH generation (SHG) experimental device. It is found that when using the open-top oven scheme and fixing the fundamental M 2-factor at nearly 1, for a range of input powers changing from 15 to 30 W, the M 2-factor of SHG beam is degraded from 9% to 24%, respectively, confirming very good consistency with the reported experimental results.
International Nuclear Information System (INIS)
Yin Jun; Yu Ling-Yao; Liu Xing; Wan Hui; Lin Zi-Yang; Niu Han-Ben
2011-01-01
In broadband coherent anti-Stokes Raman scattering (CARS) spectroscopy with supercontinuum (SC), the simultaneously detectable spectral coverage is limited by the spectral continuity and the simultaneity of various spectral components of SC in an enough bandwidth. By numerical simulations, the optimal experimental conditions for improving the SC are obtained. The broadband time-resolved CARS spectrography based on the SC with required temporal and spectral distributions is realised. The global molecular vibrational spectrum with well suppressed nonresonant background noise can be obtained in a single measurement. At the same time, the measurements of dephasing times of various molecular vibrational modes can be conveniently achieved from intensities of a sequence of time-resolved CARS signals. It will be more helpful to provide a complete picture of molecular vibrations, and to exhibit a potential to understand not only both the solvent dynamics and the solute-solvent interactions, but also the mechanisms of chemical reactions in the fields of biology, chemistry and material science. (electromagnetism, optics, acoustics, heat transfer, classical mechanics, and fluid dynamics)
Agathos, Catherine P; Bernardin, Delphine; Baranton, Konogan; Assaiante, Christine; Isableu, Brice
2017-04-07
Optic flow provides visual self-motion information and is shown to modulate gait and provoke postural reactions. We have previously reported an increased reliance on the visual, as opposed to the somatosensory-based egocentric, frame of reference (FoR) for spatial orientation with age. In this study, we evaluated FoR reliance for self-motion perception with respect to the ground surface. We examined how effects of ground optic flow direction on posture may be enhanced by an intermittent podal contact with the ground, and reliance on the visual FoR and aging. Young, middle-aged and old adults stood quietly (QS) or stepped in place (SIP) for 30s under static stimulation, approaching and receding optic flow on the ground and a control condition. We calculated center of pressure (COP) translation and optic flow sensitivity was defined as the ratio of COP translation velocity over absolute optic flow velocity: the visual self-motion quotient (VSQ). COP translation was more influenced by receding flow during QS and by approaching flow during SIP. In addition, old adults drifted forward while SIP without any imposed visual stimulation. Approaching flow limited this natural drift and receding flow enhanced it, as indicated by the VSQ. The VSQ appears to be a motor index of reliance on the visual FoR during SIP and is associated with greater reliance on the visual and reduced reliance on the egocentric FoR. Exploitation of the egocentric FoR for self-motion perception with respect to the ground surface is compromised by age and associated with greater sensitivity to optic flow. Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.
Guérin, Bastien; Stockmann, Jason P; Baboli, Mehran; Torrado-Carvajal, Angel; Stenger, Andrew V; Wald, Lawrence L
2016-08-01
To design parallel transmission spokes pulses with time-shifted profiles for joint mitigation of intensity variations due to B1+ effects, signal loss due to through-plane dephasing, and the specific absorption rate (SAR) at 7T. We derived a slice-averaged small tip angle (SA-STA) approximation of the magnetization signal at echo time that depends on the B1+ transmit profiles, the through-slice B0 gradient and the amplitude and time-shifts of the spoke waveforms. We minimize a magnitude least-squares objective based on this signal equation using a fast interior-point approach with analytical expressions of the Jacobian and Hessian. Our algorithm runs in less than three minutes for the design of two-spoke pulses subject to hundreds of local SAR constraints. On a B0/B1+ head phantom, joint optimization of the channel-dependent time-shifts and spoke amplitudes allowed signal recovery in high-B0 regions at no increase of SAR. Although the method creates uniform magnetization profiles (ie, uniform intensity), the flip angle varies across the image, which makes it ill-suited to T1-weighted applications. The SA-STA approach presented in this study is best suited to T2*-weighted applications with long echo times that require signal recovery around high B0 regions. Magn Reson Med 76:540-554, 2016. © 2015 Wiley Periodicals, Inc. © 2015 Wiley Periodicals, Inc.
The Neopuff's PEEP valve is flow sensitive.
LENUS (Irish Health Repository)
Hawkes, Colin Patrick
2012-01-31
AIM: The current recommendation in setting up the Neopuff is to use a gas flow of 5-15 L\\/min. We investigated if the sensitivity of the positive end expiratory pressure (PEEP) valve varies at different flow rates within this range. METHODS: Five Neopuffs were set up to provide a PEEP of 5 cm H(2) O. The number of clockwise revolutions to complete occlusion of the PEEP valve and the mean and range of pressures at each quarter clockwise revolution were recorded at gas flow rates between 5 and 15 L\\/min. Results: At 5, 10 and 15 L\\/min, 0.5, 1.7 and 3.4 full clockwise rotations were required to completely occlude the PEEP valve, and pressures rose from 5 to 11.4, 18.4 and 21.5 cm H(2) O, respectively. At a flow rate of 5 L\\/min, half a rotation of the PEEP dial resulted in a rise in PEEP from 5 to 11.4cm H(2) O. At 10 L\\/min, half a rotation resulted in a rise from 5 to 7.7cm H(2) O, and at 15 L\\/min PEEP rose from 5 to 6.8cm H(2) O. CONCLUSION: Users of the Neopuff should be aware that the PEEP valve is more sensitive at lower flow rates and that half a rotation of the dial at 5 L\\/min gas flow can more than double the PEEP.
The Neopuff's PEEP valve is flow sensitive.
LENUS (Irish Health Repository)
Hawkes, Colin Patrick
2011-03-01
The current recommendation in setting up the Neopuff is to use a gas flow of 5-15 L\\/min. We investigated if the sensitivity of the positive end expiratory pressure (PEEP) valve varies at different flow rates within this range.
Biexciton dephasing in a semiconductor microcavity
DEFF Research Database (Denmark)
Borri, P.; Langbein, W.; Woggon, U.
2001-01-01
the heavy-hole (HH) vacuum Rabi splitting is 3.6 meV, more than three times larger than the biexciton binding energy in the bare QW (1.1 meV). Due to the narrow linewidth of the polariton resonances, a well-resolved pump-induced optical absorption associated with biexcitons was observed. In this work we...
CASH-FLOW SENSITIVITY TO PAYMENTS FOR MATERIAL RESSOURCES
Directory of Open Access Journals (Sweden)
Lavinia Elena BRÎNDESCU OLARIU
2014-12-01
Full Text Available The financing decision is taken based on the expectations concerning the future cash-flows generated in the operating activity, which should provide coverage for the debt service and allow for an increase of the shareholders’ wealth. Still, the future cash-flows are affected by risk, which makes the sensitivity analysis a very important part of the decision process. The current research sets to evaluate the sensitivity of the payment capacity to variations of the payments for raw materials and consumables. The study employs 391 forecasted yearly cash-flow statements collected from 50 companies together with detailed information concerning the hypotheses of the forecasts. The results of the study allow for the establishment of benchmarks for the payment capacity’s sensitivity, the determination of the mechanisms through which the variation of payments for raw materials and consumables impacts the payment capacity, as well as the identification of the possible causes of such a variation.
Increased flow sensitivity from gradient recalled echoes and short TRs
International Nuclear Information System (INIS)
Hearshen, D.O.; Froelich, J.W.; Wehrli, F.W.; Haggar, A.M.; Shimakawa, A.
1986-01-01
Time-of-flight effects from flow have been characterized in spin-echo images. ''Paradoxical'' enhancement and flow void are observed. Similar enhancement is seen on GRASS images. With no flow void and gradients existing throughout the volume, spins experiencing radio-frequency pulses will give rise to signals even for fast flow, providing a greater velocity sensitivity. GRASS images were obtained from a volunteer with a blood pressure cuff placed over the right thigh. With the cuff inflated, flow in the popliteal vein results in signal saturation. Increasing TR increases intensity in the popliteal vein relative to other vessels. This suggests a clinical role for the technique in assessment of slow flow
A Flow-Sensitive Analysis of Privacy Properties
DEFF Research Database (Denmark)
Nielson, Hanne Riis; Nielson, Flemming
2007-01-01
that information I send to some service never is leaked to another service? - unless I give my permission? We shall develop a static program analysis for the pi- calculus and show how it can be used to give privacy guarantees like the ones requested above. The analysis records the explicit information flow...
Flow-sensitive type recovery in linear-log time
DEFF Research Database (Denmark)
Adams, Michael D.; Keep, Andrew W.; Midtgaard, Jan
2011-01-01
The flexibility of dynamically typed languages such as JavaScript, Python, Ruby, and Scheme comes at the cost of run-time type checks. Some of these checks can be eliminated via control-flow analysis. However, traditional control-flow analysis (CFA) is not ideal for this task as it ignores flow...
Nonequilibrium dephasing in two-dimensional indium oxide films
International Nuclear Information System (INIS)
Ovadyahu, Z.
2001-01-01
We report on results of resistance R and magnetoresistance in diffusive indium oxide films measured down to T=0.28K. Analyzing the data using weak-localization theory shows that the phase-coherent time τ v ar-phi increases without bound as T->0. However, this result is obtained only when the voltage applied to the sample V is sufficiently small. When V is not small, τ v ar-phi may appear to 'saturate' while R continues to increase as T->0. Possible reasons for this intriguing behavior are discussed. It is argued that in out-of-equilibrium situations R(T) and τ v ar-phi(T) need not behave similarly. We suggest a heuristic picture, involving two-level systems, which might be consistent with our observations
Wave attenuation model for dephasing and measurement of ...
Indian Academy of Sciences (India)
An analysis of previous models to simulate inelastic scattering in such systems is presented and a relatively new model based on wave attenuation is introduced. The problem of Aharonov–Bohm (AB) oscillations in conductance of a mesoscopic ring is studied. We show that the conductance is symmetric under ﬂux reversal ...
Entanglement dephasing dynamics driven by a bath of spins
International Nuclear Information System (INIS)
Xu Jie; Jing Jun; Yu Ting
2011-01-01
We have studied the entanglement dynamics for a two-qubit system coupled to a spin environment of different configurations by a z-x-type interaction. Quantum dynamics of the models considered in this paper is solved analytically. Moreover, we show that simple and concise results may be obtained when certain approximations are properly made. Our purpose is to find out how the entanglement of a central spin system is affected by the pre-designed factors of the system and its environment, such as their initial states and the coupling constants between the system and its environment. Clearly, how the system is coupled to its environment will inevitably change the feature of entanglement evolution of the central spin system. Our major findings include the following: (i) the entanglement of the system of interest is sensitive to the number of spins in the environment, (ii) the initial states of the environment can profoundly affect the dynamics of the entanglement of the central spin system and (iii) the entangled environment can speed up the decay and revival of the entanglement of the central spin system. Our results exhibit some interesting features that have not been found for a bosonic environment.
Dephasing of a qubit due to quantum and classical noise
Indian Academy of Sciences (India)
... a telegraph process, enebles us to set limits on the pplicability of this process à i s ... Indian Institute of Science Education and Research-Kolkata, Mohanpur 741 ... Manuscript received: 27 January 2012; Manuscript revised: 22 March 2012 ...
Zeno and anti-Zeno effects for photon polarization dephasing
Kofman, A. G.; Kurizki, G.; Opatrny, T.
2000-01-01
We discuss a simple, experimentally feasible scheme, which elucidates the principles of controlling ("engineering") the reservoir spectrum and the spectral broadening incurred by repeated measurements. This control can yield either the inhibition (Zeno effect) or the acceleration (anti-Zeno effect) of the quasi-exponential decay of the observed state by means of frequent measurements. In the discussed scheme, a photon is bouncing back and forth between two perfect mirrors, each time passing a...
Nonlocal non-Markovian effects in dephasing environments
International Nuclear Information System (INIS)
Xie Dong; Wang An-Min
2014-01-01
We study the nonlocal non-Markovian effects through local interactions between two subsystems and the corresponding two environments. It has been found that the initial correlations between two environments can turn a Markovian to a non-Markovian regime with extra control on the local interaction time. We further research the nonlocal non-Markovian effects from two situations: without extra control, the nonlocal non-Markovian effects only appear under the condition that two local dynamics are non-Markovian–non-Markovian (both of the two local dynamics are non-Markovian) or Markovian–non-Markovian, but not under the condition of Markovian–Markovian; with extra control, the nonlocal non-Markovian effects can occur under the condition of Markovian–Markovian. It shows that the function of correlations between two environments has an upper bound, which makes a flow of information from the environment back to the global system beginning finitely earlier than that back to one of the two local systems, not infinitely. Then, we proposed two special ways to distribute classical correlations between two environments without initial correlations. Finally, from numerical solutions in the spin star configuration, we found that the self-correlation (internal correlation) of each environment promotes the nonlocal non-Markovian effects. (general)
Directory of Open Access Journals (Sweden)
Dimitrios I. Maditinos
2015-10-01
Full Text Available Purpose - The existence of optimism as a personal psychological characteristic of managers is a necessity in contemporary economy and decision making, although the phenomenon of over-optimism may lead to unfavourable outcomes. The purpose of this study is to examine the optimism bias and its impact on the firms' future performance. Especially regarding the recent years where Greece faces increased economic depression, high percentages of unemployment and lack of budgetary discipline, the goal is therefore, to find whether managerial optimism has an impact on corporate investment of Greek firms. Design/methodology/approach - The investment of firms with optimistic managers is more sensitive to cash flow than the investment of firms with managers who are not optimistic. To test the research question a number of fixed effect panel regressions of capital expenditures (capital expenditures divided by lagged assets is the dependent variable is run. In all regressions we analyse cash flow divided by lagged assets and lagged Tobin's Q as the independent variables, for firms whose managers are classified as optimistic and not optimistic. This classification is based on the optimism "dummy" variable, which is equal to 1 when members of the Executive Board and the Supervisory Board (ALL, only the Executive Board (EB, and only CEO are classified as optimistic. The concept of this study is tested for firms which are listed in the Athens Stock Exchange. A total of 243 firms are recorded, for the time period between 2007 and 2012, including firms from 11 different industries; basic materials, chemicals, consumer goods, consumer services, health care, industrials, financials, oil and gas, technology, telecommunications and utilities. Based on the literature and on related methodology aspects, financial firms are excluded. Findings - It was revealed that managerial optimism affects corporate investment in firms with high degree of closely held shares. Moreover, managerial optimism is never linked to corporate investment regarding firms which belong to middle degree of closely held shares. Additionally it is proved that decisions for acquisitions are not affected by the manager's optimism regarding the prospects of his / her firm. This result it is not consistent with results of previous literature like Malmendier and Tate (2008 and Glaser et al. (2008 who have found that cash flow, Tobin's Q and firm size mainly drive the probability of an acquisition. Finally, it is confirmed that investment of firms with optimistic managers was found to be more sensitive to cash flow than the investment of firms with managers who are not optimistic. Optimism was proved to be extremely effective concerning investment. Research limitations/implications - A possible proposal for further research could be the testing of each year separately. In this study we have run the regressions for the whole of the 6-year period of 2007 to 2012. However, testing each year individually could provide researchers with the ability to compare different results, to find out whether there was anything special statistically for each specific year and maybe test the period after the year 2010 when the Greek crisis had started to come up on the horizon. The impact of the Greek financial crisis on managerial behaviour and on the personal characteristics of managers like optimism could constitute a field for further research. Originality/value - Since research on this specific field of finance is quite limited; this study aims to add value on the existing knowledge on the Greek case. The investigation of managerial optimism as a personal, psychological and mental characteristic encloses the effort of Greek managers to come out of the economic crisis and consequently achieve greater outcomes for their firms.
The marginal value of cash, cash flow sensitivities, and bank-finance shocks in nonlisted firms
Ostergaard, Charlotte; Sasson, Amir; Sørensen, Bent E
2011-01-01
We study how nonlisted firms trade off financial, real, and distributive uses of cash. We show that firms' marginal value of cash (MVC) affects the mix of external and internal finance used to absorb fluctuations in cash flows; in particular, high-MVC firms employ substantially more external finance on the margin. Linking firms to their main bank, we find that shocks to bank finance affect firms' trade-offs and have real effects in high-MVC firms, making investment more sensitiv...
Artificial sensory hairs based on the flow sensitive receptor hairs of crickets
Dijkstra, Marcel; van Baar, J.J.J.; Wiegerink, Remco J.; Lammerink, Theodorus S.J.; de Boer, J.H.; Krijnen, Gijsbertus J.M.
2005-01-01
This paper presents the modelling, design, fabrication and characterization of flow sensors based on the wind-receptor hairs of crickets. Cricket sensory hairs are highly sensitive to drag-forces exerted on the hair shaft. Artificial sensory hairs have been realized in SU-8 on suspended SixNy
Non-Markovian phonon dephasing of a quantum dot in a photonic-crystal nanocavity
DEFF Research Database (Denmark)
Madsen, Kristian Høeg; Nielsen, Per Kær; Kreiner-Møller, Asger
2012-01-01
this model, we are able to explain the broadband enhancement in an L3 cavity, and the quantitative difference compared to the AL-cavity arises from a larger background decay rate in the AL-cavity due to the presence of leaky radiation modes. The concept of the effective phonon density of states (DOS...
Room-temperature dephasing in InAs/GaAs quantum dots
DEFF Research Database (Denmark)
Borri, Paola; Langbein, Wolfgang; Hvam, Jørn Märcher
1999-01-01
Summary form only given. Semiconductor quantum dots (QDs) are receiving increasing attention for fundamental studies on zero-dimensional confinement and for device applications. Quantum-dot lasers are expected to show superior performances, like high material gain, low and temperature...... stacked layers of InAs-InGaAs-GaAs quantum dots....
International Nuclear Information System (INIS)
Zhang Ming; Dai Hongyi; Xi Zairong; Xie Hongwei; Hu Dewen
2007-01-01
We propose a scheme to overcome phase damping decoherence by periodically performing open loop tracking control and projective measurement. Although it is impossible to stabilize a qubit subject to Markovian dynamics only by open loop coherent control, one can attain a 'softened' control goal with the help of periodical projective measurement. The 'softened' control objective in our scheme is to keep the state of the controlled qubit to stay near a reference pure state with a high probability for a sufficiently long time. Two suboptimal control problems are given in the sense of trace distance and fidelity, respectively, and they are eventually reduced to the design of a period T. In our scheme, one can choose the period T as long as possible if the 'softened' control goal is attained. This is in contrast to the observation that quantum Zeno effect takes place only if measurements are performed in a very frequent manner, i.e., the period T must be extremely small
Interaction of an electron with coherent dipole radiation: Role of convergence and anti-dephasing
Robinson, A. P. L.; Arefiev, A. V.
2018-05-01
The impact of longitudinal electric fields that are present in intense focusing and defocusing electromagnetic pulses on electron acceleration is investigated. These fields are typically much weaker than the transverse fields, but it is shown that they can have a profound effect on electron energy gain. It is shown that the longitudinal electric field of a defocusing pulse is directed backward along the trajectory of an accelerated electron, which leads to a continuous net energy gain. At the same time, the effect of the transverse oscillating electric field in a defocusing pulse is to reduce the electron energy over multiple oscillations. In contrast to a well-known interaction with a plane wave, the electron is able to retain a substantial amount of energy following its interaction with a defocusing pulse. The roles of the transverse and longitudinal electric fields are reversed in a focusing pulse, which leads to a reduction in the energy retention. The present analysis underscores the importance of relatively weak oscillating electric fields in focusing and defocusing pulses.
Optimal pulse spacing for dynamical decoupling in the presence of a purely dephasing spin bath
International Nuclear Information System (INIS)
Ajoy, Ashok; Alvarez, Gonzalo A.; Suter, Dieter
2011-01-01
Maintaining quantum coherence is a crucial requirement for quantum computation; hence protecting quantum systems against their irreversible corruption due to environmental noise is an important open problem. Dynamical decoupling (DD) is an effective method for reducing decoherence with a low control overhead. It also plays an important role in quantum metrology, where, for instance, it is employed in multiparameter estimation. While a sequence of equidistant control pulses [the Carr-Purcell-Meiboom-Gill (CPMG) sequence] has been ubiquitously used for decoupling, Uhrig recently proposed that a nonequidistant pulse sequence [the Uhrig dynamic decoupling (UDD) sequence] may enhance DD performance, especially for systems where the spectral density of the environment has a sharp frequency cutoff. On the other hand, equidistant sequences outperform UDD for soft cutoffs. The relative advantage provided by UDD for intermediate regimes is not clear. In this paper, we analyze the relative DD performance in this regime experimentally, using solid-state nuclear magnetic resonance. Our system qubits are 13 C nuclear spins and the environment consists of a 1 H nuclear spin bath whose spectral density is close to a normal (Gaussian) distribution. We find that in the presence of such a bath, the CPMG sequence outperforms the UDD sequence. An analogy between dynamical decoupling and interference effects in optics provides an intuitive explanation as to why the CPMG sequence performs better than any nonequidistant DD sequence in the presence of this kind of environmental noise.
Interplay between Dephasing and Geometry and Directed Heat Flow in Exciton Transfer Complexes
Dubi, Yonatan
2015-01-01
The striking efficiency of energy transfer in natural photosynthetic systems and the recent evidence of long-lived quantum coherence in biological light harvesting complexes has triggered much excitement, due to the evocative possibility that these systems - essential to practically all life on earth -- use quantum mechanical effects to achieve optimal functionality. A large body of theoretical work has addressed the role of local environments in determining the transport properties of excito...
Interaction and Dephasing of Excitons in ZnSe Quantum Wires
DEFF Research Database (Denmark)
Wagner, Hans Peter; Langbein, Wolfgang; Hvam, Jørn Märcher
1999-01-01
We study the coherent formation of biexcitons in wet-etched ZnSe quantum wires of lateral sizes down to 23 nm by transient degenerate four-wave mixing. We observe an increase of the biexciton binding energy with decreasing wire width reaching 30% energy enhancement in the smallest wire structure...
DEFF Research Database (Denmark)
Unsleber, Sebastian; McCutcheon, Dara; Dambach, Michael
2015-01-01
We demonstrate the emission of highly indistinguishable photons from a quasi-resonantly pumped coupledquantum dot–microcavity system operating in the regime of cavity quantum electrodynamics. Changing thesample temperature allows us to vary the quantum dot–cavity detuning and, on spectral resonance...
DEFF Research Database (Denmark)
Unsleber, S.; McCutcheon, Dara; Dambach, M.
We demonstrate the emission of highly indistinguishable photons from a quasiresonantly pumped coupled quantum dot–microcavity system operating in the regime of cavity quantum electrodynamics. Changing the sample temperature allows us to vary the quantum dot–cavity detuning, and on spectral...
Rivas, Eric; McEntire, Serina J; Herndon, David N; Mlcak, Ronald P; Suman, Oscar E
2017-05-01
We tested the hypothesis that propranolol, a drug given to burn patients to reduce hypermetabolism/cardiac stress, may inhibit heat dissipation by changing the sensitivity of skin blood flow (SkBF) to local heating under neutral and hot conditions. In a randomized double-blind study, a placebo was given to eight burned children, while propranolol was given to 13 burned children with similar characteristics (mean±SD: 11.9±3 years, 147±20 cm, 45±23 kg, 56±12% Total body surface area burned). Nonburned children (n=13, 11.4±3 years, 152±15 cm, 52±13 kg) served as healthy controls. A progressive local heating protocol characterized SkBF responses in burned and unburned skin and nonburned control skin under the two environmental conditions (23 and 34°C) via laser Doppler flowmetry. Resting SkBF was greater in burned and unburned skin compared to the nonburned control (main effect: skin, Pburned; 38±36 unburned vs 9±8 control %SkBF max ). No difference was found for maximal SkBF capacity to local heating between groups. Additionally, dose-response curves for the sensitivity of SkBF to local heating were not different among burned or unburned skin, and nonburned control skin (EC 50 , P>.05) under either condition. Therapeutic propranolol does not negatively affect SkBF under neutral or hot environmental conditions and further compromise temperature regulation in burned children. © 2017 John Wiley & Sons Ltd.
DEFF Research Database (Denmark)
Nielsen, Per Kær; Nielsen, Torben Roland; Lodahl, Peter
2010-01-01
treatments. A pronounced consequence is the emergence of a phonon induced spectral asymmetry when detuning the cavity from the quantum-dot resonance. The asymmetry can only be explained when considering the polaritonic quasiparticle nature of the quantum-dot-cavity system. Furthermore, a temperature induced...
Czech Academy of Sciences Publication Activity Database
Menšík, Miroslav; Král, Karel
2009-01-01
Roč. 27, č. 3 (2009), s. 671-684 ISSN 0137-1339. [International Conference on Electrical and Related Properties of Organic Solids /11./. Piechowice, 13.07.2008-17.07.2008] R&D Projects: GA AV ČR KAN401770651; GA ČR GA202/07/0643 Institutional research plan: CEZ:AV0Z40500505; CEZ:AV0Z10100520 Keywords : electron-vibrational interaction * non-adiabatic coupling * resonant energy transfer Subject RIV: CD - Macromolecular Chemistry Impact factor: 0.384, year: 2009
Rivas, Eric; McEntire, Serina J.; Herndon, David N.; Mlcak, Ronald P.; Suman, Oscar E.
2017-01-01
Objective Tested the hypothesis that propranolol, a drug given to burn patients to reduce hypermetabolism/cardiac stress, may inhibit heat dissipation by changing the sensitivity of skin blood flow (SkBF) to local heating under neutral and hot conditions. Methods In a randomized double-blind study, a placebo was given to 8 burned children while propranolol was given to 13 burned children with similar characteristics (mean ± SD: 11.9±3y, 147±20cm, 45±23kg, 56±12% TBSA). Non-burned children (n=13, 11.4±3y, 152±15cm, 52±13kg) served as healthy controls. A progressive local heating protocol characterized SkBF responses in burned and unburned skin and non-burned control skin under the two environmental conditions (23°C and 34°C) via laser-Doppler flowmetry. Results Resting SkBF was greater in burned and unburned skin compared to the non-burned control (main effect: skin, Pburned; 38±36 unburned vs 9±8 control %SkBFmax). No difference was found for maximal SkBF capacity to local heating between groups. Additionally, dose response curves for the sensitivity of SkBF to local heating were not different among burned or unburned skin, and non-burned control skin (EC50, P>0.05) under either condition. Conclusion Therapeutic propranolol does not negatively affect SkBF under neutral or hot environmental conditions and further compromise temperature regulation in burned children. PMID:28071840
International Nuclear Information System (INIS)
Babbitt, W.R.; Lezama, A.; Mossberg, T.W.
1989-01-01
We have employed spectral-hole-burning, coherent-transient, and optical-rf double-resonance techniques to measure various parameters associated with the 580.8-nm 7 F 0 - 5 D 0 transition of Eu/sup 3+/ doped into Y 2 O 3 . In particular, we have measured the hyperfine splittings of the terminal levels (for both /sup 151/Eu and /sup 153/Eu), an effective thermalization rate of the ground-state ( 7 F 0 ) hyperfine manifold over the temperature range of ≅4--15 K, and the homogeneous linewidth of the optical transition over the range of ≅14--35 K. Large ratios of inhomogeneous to homogeneous linewidth at elevated temperatures (10 3 at 25 K) and long ground-state hyperfine thermalization times (>30 h at 4 K) make this an interesting crystal in the context of spectrally addressable optical memories
Well-width dependence of exciton-phonon scattering in InxGa1 - xAs/GaAs single quantum wells
DEFF Research Database (Denmark)
Borri, Paola; Langbein, Wolfgang Werner; Hvam, Jørn Märcher
1999-01-01
The temperature and density dependencies of the exciton dephasing time in In0.18Ga0.82As/GaAs single quantum wells with different thicknesses have been measured by degenerate four-wave mixing; The exciton-phonon scattering contribution to the dephasing is isolated by extrapolating the dephasing r...
Enhanced quantum coherence in graphene caused by Pd cluster deposition
International Nuclear Information System (INIS)
Qin, Yuyuan; Han, Junhao; Du, Yongping; Li, Zhaoguo; Wan, Xiangang; Han, Min; Song, Fengqi; Guo, Guoping; Song, You; Pi, Li; Wang, Xuefeng
2015-01-01
We report on the unexpected increase in the dephasing lengths of a graphene sheet caused by the deposition of Pd nanoclusters, as demonstrated by weak localization measurements. The dephasing lengths reached saturated values at low temperatures. Theoretical calculations indicate the p-type charge transfer from the Pd clusters, which contributes more carriers. The saturated values of dephasing lengths often depend on both the carrier concentration and mean free path. Although some impurities are increased as revealed by decreased mobilities, the intense charge transfer leads to the improved saturated values and subsequent improved dephasing lengths
Timescales of Coherent Dynamics in the Light Harvesting Complex 2 (LH2) of Rhodobacter sphaeroides.
Fidler, Andrew F; Singh, Ved P; Long, Phillip D; Dahlberg, Peter D; Engel, Gregory S
2013-05-02
The initial dynamics of energy transfer in the light harvesting complex 2 from Rhodobacter sphaeroides were investigated with polarization controlled two-dimensional spectroscopy. This method allows only the coherent electronic motions to be observed revealing the timescale of dephasing among the excited states. We observe persistent coherence among all states and assign ensemble dephasing rates for the various coherences. A simple model is utilized to connect the spectroscopic transitions to the molecular structure, allowing us to distinguish coherences between the two rings of chromophores and coherences within the rings. We also compare dephasing rates between excited states to dephasing rates between the ground and excited states, revealing that the coherences between excited states dephase on a slower timescale than coherences between the ground and excited states.
Coherence properties and quantum state transportation in an optical conveyor belt.
Kuhr, S; Alt, W; Schrader, D; Dotsenko, I; Miroshnychenko, Y; Rosenfeld, W; Khudaverdyan, M; Gomer, V; Rauschenbeutel, A; Meschede, D
2003-11-21
We have prepared and detected quantum coherences of trapped cesium atoms with long dephasing times. Controlled transport by an "optical conveyor belt" over macroscopic distances preserves the atomic coherence with slight reduction of coherence time. The limiting dephasing effects are experimentally identified, and we present an analytical model of the reversible and irreversible dephasing mechanisms. Our experimental methods are applicable at the single-atom level. Coherent quantum bit operations along with quantum state transport open the route towards a "quantum shift register" of individual neutral atoms.
Hole spin coherence in a Ge/Si heterostructure nanowire
DEFF Research Database (Denmark)
Higginbotham, Andrew P; Larsen, Thorvald Wadum; Yao, Jun
2014-01-01
Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si nanowire double quantum dot using a fast pulsed-gate method and dispersive readout. An inhomogeneous dephasing time T2(*)≈ 0.18 μs exceeds corresponding measurements in III-V semiconductors by more than an order of magnit......Relaxation and dephasing of hole spins are measured in a gate-defined Ge/Si nanowire double quantum dot using a fast pulsed-gate method and dispersive readout. An inhomogeneous dephasing time T2(*)≈ 0.18 μs exceeds corresponding measurements in III-V semiconductors by more than an order...
Thermalization as an Invisibility Cloak for Fragile Quantum Superpositions
Hahn, Walter; Fine, Boris V.
2017-01-01
We propose a method for protecting fragile quantum superpositions in many-particle systems from dephasing by external classical noise. We call superpositions "fragile" if dephasing occurs particularly fast, because the noise couples very differently to the superposed states. The method consists of letting a quantum superposition evolve under the internal thermalization dynamics of the system, followed by a time reversal manipulation known as Loschmidt echo. The thermalization dynamics makes t...
Coherent Exciton and Biexciton Nonlinearities in Semiconductor Nanostructures: Effects of Disorder
DEFF Research Database (Denmark)
Langbein, Wolfgang; Borri, Paola; Hvam, Jørn Märcher
1999-01-01
-space filling nonlinearity, excitation-induced dephasing (EID) and biexciton formation (BIF) are important. EID leads to a strong dependence of the signal on the angle between the linear input polarizations. We find that EID persists in inhomogeneous systems, showing that the mutual density-dependent dephasing...... and non-exponential signal decay in delay time. For inhomogenous broadenings larger than the biexciton binding energy, we find an enhanced biexciton binding energy, and a quenching of the oscillator strength of the unbound biexciton....
Spin noise spectroscopy of ZnO
Horn, H.; Berski, F.; Balocchi, A.; Marie, X.; Mansur-Al-Suleiman, M.; Bakin, A.; Waag, A.; Hübner, J.; Oestreich, M.
2013-12-01
We investigate the thermal equilibrium dynamics of electron spins bound to donors in nanoporous ZnO by optical spin noise spectroscopy. The spin noise spectra reveal two noise contributions: A weak spin noise signal from undisturbed localized donor electrons with a dephasing time of 24 ns due to hyperfine interaction and a strong spin noise signal with a spin dephasing time of 5 ns which we attribute to localized donor electrons which interact with lattice defects.
Spin noise spectroscopy of ZnO
Energy Technology Data Exchange (ETDEWEB)
Horn, H.; Berski, F.; Hübner, J.; Oestreich, M. [Institute for Solid State Physics, Leibniz Universität Hannover, Appelstr. 2, 30167 Hannover (Germany); Balocchi, A.; Marie, X. [INSA-CNRS-UPS, LPCNO, Université de Toulouse, 135 Av. de Rangueil, 31077 Toulouse (France); Mansur-Al-Suleiman, M.; Bakin, A.; Waag, A. [Institute of Semiconductor Technology, Technische Universität Braunschweig, Hans-Sommer-Straße 66, 38106 Braunschweig (Germany)
2013-12-04
We investigate the thermal equilibrium dynamics of electron spins bound to donors in nanoporous ZnO by optical spin noise spectroscopy. The spin noise spectra reveal two noise contributions: A weak spin noise signal from undisturbed localized donor electrons with a dephasing time of 24 ns due to hyperfine interaction and a strong spin noise signal with a spin dephasing time of 5 ns which we attribute to localized donor electrons which interact with lattice defects.
International Nuclear Information System (INIS)
Seiderer, M.
1989-01-01
Three categories of MRI techniques for vascular imaging are discussed: 2d-angiography using rephasing and dephasing pulse sequences and slice selective imaging; 3d-angiography using rehpasing and dephasing pulse sequences and fas 3d-imaging techniques; 3d-angiography using signal intensity modulation caused by pre- and post-contrast data acquisition (e.g. Gadolinium-DTPA) in combination with fast 3d-imaging (only one type of pulse sequence). (H.W.). 6 figs
Electric Dipole Echoes and Noise-Induced Coherence
International Nuclear Information System (INIS)
Mestayer, J.J.; Zhao, W.; Lancaster, J.C.; Dunning, F.B.; Yoshida, S.; Reinhold, Carlos O.; Burgdorfer, J.
2007-01-01
The generation of echoes in the electric dipole moment of a Rydberg wavepacket precessing in an external electric field by reversal of the field is described. When the wavepacket experiences reversible dephasing, large echoes are observed pointing to strong refocusing of the wavepacket. The presence of irreversible dephasing leads to a reduction in the size of the echoes. The effect of irreversible dynamics on echoes is investigated using artificially synthesized noise. Methods to determine the decoherence rate are discussed
DRAMAtic transforms in magic angle spinning recoupling NMR: The Bessel function pathway.
Goodman, Russell; Hancock, Jason; Siemens, Mark; Jarrell, Harold; Siminovitch, David
2005-07-01
In magic angle spinning (MAS) NMR recoupling experiments, the extraction of multiple couplings or a coupling distribution from the observed dephasing signals remains a challenging problem. At least for REDOR experiments, the REDOR transform solves this problem, enabling the simultaneous measurement of multiple dipolar couplings. Focusing on the quadrupolar dephasing observed in QUADRAMA experiments as a representative example, we demonstrate that the same analytical form used for the mathematical description of REDOR dephasing also describes the dephasing observed in a wide variety of MAS NMR recoupling experiments. This fact immediately extends REDOR transform techniques to a much broader suite of recoupling experiments than had previously been realized, including those of DRAMA, MELODRAMA and QUADRAMA. As an illustration, we use the DRAMAtic transform to provide the first inversion of a QUADRAMA dephasing signal to extract the quadrupole coupling distribution. Using a complete elliptic integral of the first kind, we further develop a novel expression for the Pake-spun powder patterns of the corresponding recoupled lineshapes. Our methods and results reinforce the central role that Bessel functions can play in simplifying the integrals that define both the dephasing signals in the time domain, and their Fourier transforms in the frequency domain.
Birman, Joseph L.; Kuklov, A. B.
2001-05-01
The concept of the orthogonality catastrophe (OC), which has been introduced previously for one component condensate ( A.B. Kuklov, J.L. Birman, PRA 63), 013609 (2001), is applied to the two-component condensate. The evolution of the global relative phase, which is created by the rf-pulse, is studied under the condition of no exchange of bosons between the components after the pulse. It is shown that the normal component does not induce the OC. Instead, it produces a reversible thermal dephasing, which competes with the quantum phase diffusion (QPD) effect (E.M.Wright, et al, PRL 77), 2158(1996). The thermal dephasing results from the thermal ensemble averaging, and the corresponding dephasing rate is controlled by the two-body interaction and temperature as well as by the closeness to the intrinsic su(2) symmetry, so that no dephasing exists in the case of the exact symmetry (A.B. Kuklov, J.L. Birman, PRL 85), 5488 (2000). The reversible nature of the thermal dephasing as well as of the QPD can be revealed in the atomic echo effect. The role of external noise in erasing the phase memory is discussed as well.
Spin coherence in phosphorescent triplet states
International Nuclear Information System (INIS)
Hof, C.A. van 't
1977-01-01
The electron spin echo is studied on the dephasing mechanism in the photo-excited triplet state of quinoline in a durene host. First, a comparative investigation of the merits of the different spin echo techniques is presented. It turns out that the rotary echo generally yields a longer phase memory time than the two-pulse echo, whereas in the Carr-Purcell experiment, the dephasing can even be largely suppressed. Secondly, it is shown that the dephasing mechanism is determined by the nuclear spins of the guest molecules as well as those in the host material. A theoretical basis for interpreting the effect of vibronic relaxation on the decay rate of the rotary echo, as observed in parabenzoquinone, is given. Similar experiments in aniline reveal also that in this molecule, two close-lying triplet states exist, which is attributed to an inversion vibration analogous to the well-known example in ammonia
Correlation effect of Rabi oscillations of excitons in quantum dots
International Nuclear Information System (INIS)
Ishi-Hayase, J.; Akahane, K.; Yamamoto, Y.; Kujiraoka, M.; Ema, K.; Sasaki, M.
2008-01-01
We performed a transient four-wave mixing experiment on a strain-compensated InAs quantum dot (QD) ensemble over a wide range of excitation intensities. Under the resonant excitation of an exciton ground state, an extremely long dephasing time of 1 ns was found. By increasing the areas of the excitation pulses, Rabi oscillations of excitonic polarizations were clearly observed. The corresponding Rabi frequency is three orders of magnitude higher than the measured dephasing rate. For larger pulse areas, we found that the deviation of experimental data from two-level predictions became significant. The deviations cannot be explained by taking into account, as has been suggested in other research, excitation density-dependent dephasing or Hartree-Fock-type Coulomb interactions between excitons
Directory of Open Access Journals (Sweden)
Isidoro Martinez
2015-11-01
Full Text Available We investigate the influence of an external magnetic field on the magnitude and dephasing of the transient lateral photovoltaic effect (T-LPE in lithographically patterned Co lines of widths of a few microns grown over naturally passivated p-type Si(100. The T-LPE peak-to-peak magnitude and dephasing, measured by lock-in or through the characteristic time of laser OFF exponential relaxation, exhibit a notable influence of the magnetization direction of the ferromagnetic overlayer. We show experimentally and by numerical simulations that the T-LPE magnitude is determined by the Co anisotropic magnetoresistance. On the other hand, the magnetic field dependence of the dephasing could be described by the influence of the Lorentz force acting perpendiculary to both the Co magnetization and the photocarrier drift directions. Our findings could stimulate the development of fast position sensitive detectors with magnetically tuned magnitude and phase responses.
de Haan, Hendrick W; Paquet, Chantal
2011-12-01
The effects of including a hydrophilic coating around the particles are studied across a wide range of particle sizes by performing Monte Carlo simulations of protons diffusing through a system of magnetic particles. A physically realistic methodology of implementing the coating by cross boundary jump scaling and transition probabilities at the coating surface is developed. Using this formulation, the coating has three distinct impacts on the relaxation rate: an enhancement at small particle sizes, a degradation at intermediate particle sizes, and no effect at large particles sizes. These varied effects are reconciled with the underlying dephasing mechanisms by using the concept of a full dephasing zone to present a physical picture of the dephasing process with and without the coating for all sizes. The enhancement at small particle sizes is studied systemically to demonstrate the existence of an optimal ratio of diffusion coefficients inside/outside the coating to achieve maximal increase in the relaxation rate. Copyright © 2011 Wiley Periodicals, Inc.
Spin dynamics in bulk CdTe at room temperature
International Nuclear Information System (INIS)
Nahalkova, P.; Nemec, P.; Sprinzl, D.; Belas, E.; Horodysky, P.; Franc, J.; Hlidek, P.; Maly, P.
2006-01-01
In this paper, we report on the room temperature dynamics of spin-polarized carriers in undoped bulk CdTe. Platelets of CdTe with different concentration of preparation-induced dislocations were prepared by combining the mechanical polishing and chemical etching. Using the polarization-resolved pump-probe experiment in transmission geometry, we have observed a systematic decrease of both the signal polarization and the electron spin dephasing time (from 52 to 36 ps) with the increased concentration of defects. We have suggested that the Elliot-Yafet mechanism might be the dominant spin dephasing mechanism in platelets of CdTe at room temperature
Thermalization as an invisibility cloak for fragile quantum superpositions
Hahn, Walter; Fine, Boris V.
2017-07-01
We propose a method for protecting fragile quantum superpositions in many-particle systems from dephasing by external classical noise. We call superpositions "fragile" if dephasing occurs particularly fast, because the noise couples very differently to the superposed states. The method consists of letting a quantum superposition evolve under the internal thermalization dynamics of the system, followed by a time-reversal manipulation known as Loschmidt echo. The thermalization dynamics makes the superposed states almost indistinguishable during most of the above procedure. We validate the method by applying it to a cluster of spins ½.
Entanglement fidelity of quantum memories
International Nuclear Information System (INIS)
Surmacz, K.; Nunn, J.; Waldermann, F. C.; Wang, Z.; Walmsley, I. A.; Jaksch, D.
2006-01-01
We introduce a figure of merit for a quantum memory which measures the preservation of entanglement between a qubit stored in and retrieved from the memory and an auxiliary qubit. We consider a general quantum memory system consisting of a medium of two level absorbers, with the qubit to be stored encoded in a single photon. We derive an analytic expression for our figure of merit taking into account Gaussian fluctuations in the Hamiltonian parameters, which, for example, model inhomogeneous broadening and storage time dephasing. Finally we specialize to the case of an atomic quantum memory where fluctuations arise predominantly from Doppler broadening and motional dephasing
Robustness of multiparty nonlocality to local decoherence
International Nuclear Information System (INIS)
Jang, Sung Soon; Cheong, Yong Wook; Kim, Jaewan; Lee, Hai-Woong
2006-01-01
We investigate the robustness of multiparty nonlocality under local decoherence, acting independently and equally on each subsystem. To be specific, we consider an N-qubit Greenberger-Horne-Zeilinger (GHZ) state under a depolarization, dephasing, or dissipation channel, and examine nonlocality by testing violation of the Mermin-Klyshko inequality, which is one of Bell's inequalities for multiqubit systems. The results show that the robustness of nonlocality increases with the number of qubits, and that the nonlocality of an N-qubit GHZ state with even N is extremely persistent against dephasing
Measuring the effective phonon density of states of a quantum dot in cavity quantum electrodynamics
DEFF Research Database (Denmark)
Madsen, Kristian Høeg; Nielsen, Per Kær; Kreiner-Møller, Asger
2013-01-01
We employ detuning-dependent decay-rate measurements of a quantum dot in a photonic-crystal cavity to study the influence of phonon dephasing in a solid-state quantum-electrodynamics experiment. The experimental data agree with a microscopic non-Markovian model accounting for dephasing from...... longitudinal acoustic phonons, and the analysis explains the difference between nonresonant cavity feeding in different nanocavities. From the comparison between experiment and theory we extract the effective phonon density of states experienced by the quantum dot in the nanocavity. This quantity determines...
Mode locking of electron spin coherences in singly charged quantum dots.
Greilich, A; Yakovlev, D R; Shabaev, A; Efros, Al L; Yugova, I A; Oulton, R; Stavarache, V; Reuter, D; Wieck, A; Bayer, M
2006-07-21
The fast dephasing of electron spins in an ensemble of quantum dots is detrimental for applications in quantum information processing. We show here that dephasing can be overcome by using a periodic train of light pulses to synchronize the phases of the precessing spins, and we demonstrate this effect in an ensemble of singly charged (In,Ga)As/GaAs quantum dots. This mode locking leads to constructive interference of contributions to Faraday rotation and presents potential applications based on robust quantum coherence within an ensemble of dots.
Quantum coherence in photo-ionisation with tailored XUV pulses
Carlström, Stefanos; Mauritsson, Johan; Schafer, Kenneth J.; L'Huillier, Anne; Gisselbrecht, Mathieu
2018-01-01
Ionisation with ultrashort pulses in the extreme ultraviolet (XUV) regime can be used to prepare an ion in a superposition of spin-orbit substates. In this work, we study the coherence properties of such a superposition, created by ionising xenon atoms using two phase-locked XUV pulses at different frequencies. In general, if the duration of the driving pulse exceeds the quantum beat period, dephasing will occur. If however, the frequency difference of the two pulses matches the spin-orbit splitting, the coherence can be efficiently increased and dephasing does not occur.
Controlling the net charge on a nanoparticle optically levitated in vacuum
Frimmer, Martin; Luszcz, Karol; Ferreiro, Sandra; Jain, Vijay; Hebestreit, Erik; Novotny, Lukas
2017-06-01
Optically levitated nanoparticles in vacuum are a promising model system to test physics beyond our current understanding of quantum mechanics. Such experimental tests require extreme control over the dephasing of the levitated particle's motion. If the nanoparticle carries a finite net charge, it experiences a random Coulomb force due to fluctuating electric fields. This dephasing mechanism can be fully excluded by discharging the levitated particle. Here, we present a simple and reliable technique to control the charge on an optically levitated nanoparticle in vacuum. Our method is based on the generation of charges in an electric discharge and does not require additional optics or mechanics close to the optical trap.
Coherent or hopping like energy transfer in the chlorosome ?
Nalbach, Peter
2014-08-01
Chlorosomes, as part of the light-harvesting system of green bacteria, are the largest and most efficient antennae systems in nature. We have studied energy transfer dynamics in the chlorosome in a simplified toy model employing a master equation. Dephasing and relaxation due to environmental fluctuations are included by Lindblad dephasing and Redfield thermalization rates. We find at room temperature three separate time scales, i.e. 25 fs, 250 fs and 2.5 ps and determine the according energy pathways through the hierarchical structure in the chlorosome. Quantum coherence lives up to 150 fs at which time the energy is spread over roughly 12 pigments in our model.
A short TE gradient-echo sequence using asymmetric sampling
International Nuclear Information System (INIS)
Fujita, Norihiko; Harada, Kohshi; Sakurai, Kosuke; Nakanishi, Katsuyuki; Kim, Shyogen; Kozuka, Takahiro
1990-01-01
We have developed a gradient-echo pulse sequence with a short TE less than 4 msec using a data set of asymmetric off-center sampling with a broad bandwidth. The use of such a short TE significantly reduces T 2 * dephasing effect even in a two-dimensional mode, and by collecting an off-center echo, motion-induced phase dispersion is also considerably decreased. High immunity of this sequence to these dephasing effects permits clear visualization of anatomical details near the skull base where large local field inhomogeneities and rapid blood flow such as in the internal carotid artery are present. (author)
Error Distributions on Large Entangled States with Non-Markovian Dynamics
DEFF Research Database (Denmark)
McCutcheon, Dara; Lindner, Netanel H.; Rudolph, Terry
2014-01-01
We investigate the distribution of errors on a computationally useful entangled state generated via the repeated emission from an emitter undergoing strongly non-Markovian evolution. For emitter-environment coupling of pure-dephasing form, we show that the probability that a particular patten...... of errors occurs has a bound of Markovian form, and thus, accuracy threshold theorems based on Markovian models should be just as effective. Beyond the pure-dephasing assumption, though complicated error structures can arise, they can still be qualitatively bounded by a Markovian error model....
International Nuclear Information System (INIS)
George, S.M.; Harris, C.B.
1982-01-01
The dependence of inhomogeneous vibrational linewidth broadening on attractive forces form slowly varying local liquid number densities is examined. The recently developed Schweizer--Chandler theory of vibrational dephasing is used to compute absolute inhomogeneous broadening linewidths. The computed linewidths are compared to measured inhomogeneous broadening linewidths determined using picosecond vibrational dephasing experiments. There is a similarity between correlations of the Schweizer--Chandler and George--Auweter--Harris predicted inhomogeneous broadening linewidths and the measured inhomogeneous broadening linewidths. For the methyl stretches under investigation, this correspondence suggests that the width of the number density distribution in the liquid determines the relative inhomogeneous broadening magnitudes
Energy Technology Data Exchange (ETDEWEB)
Xie Li; Ghosh, Ujjayini; Schmick, Scott D.; Weliky, David P., E-mail: weliky@chemistry.msu.edu [Michigan State University, Department of Chemistry (United States)
2013-01-15
Residue-specific location of peptides in the hydrophobic core of membranes was examined using {sup 13}C-{sup 2}H REDOR and samples in which the lipids were selectively deuterated. The transmembrane topology of the KALP peptide was validated with this approach with substantial dephasing observed for deuteration in the bilayer center and reduced or no dephasing for deuteration closer to the headgroups. Insertion of {beta} sheet HIV and helical and {beta} sheet influenza virus fusion peptides into the hydrophobic core of the membrane was validated in samples with extensively deuterated lipids.
Pramana – Journal of Physics | Indian Academy of Sciences
Indian Academy of Sciences (India)
The partial density of states play a prominent role in measurements with a scanning tunneling microscope on multiprobe conductors in the presence of current ﬂow. The partial density of states determine the degree of dephasing generated by a weakly coupled voltage probe. In addition the partial density of states determine ...
DEFF Research Database (Denmark)
Birkedal, Dan; Vadim, Lyssenko; Pantke, Karl-Heinz
1995-01-01
The interface roughness on a nanometer scale plays a decisive role in dephasing of excitons in GaAs multiple quantum wells. The excitonic four-wave mixing signal shows a free polarization decay and a corresponding homogeneously broadened line from areas with interface roughness on a scale larger...
Absence of hyperfine effects in 13C-graphene spin-valve devices
Wojtaszek, M.; Vera-Marun, I.J.; Whiteway, E.; Hilke, M.; Wees, B.J. van
2014-01-01
The carbon isotope 13C, in contrast to 12C, possesses a nuclear magnetic moment and can induce electron spin dephasing in graphene. This effect is usually neglected due to the low abundance of 13C in natural carbon allotropes (~1%). Chemical vapor deposition (CVD) allows for artificial synthesis of
DEFF Research Database (Denmark)
Madsen, Kristian Høeg; Ates, Serkan; Reitzenstein, S.
2010-01-01
The coupling between a quantum dot (QD) and a micropillar cavity is experimentally investigated by performing time-resolved, correlation, and two-photon interference measurements. The Jaynes-Cummings model including dissipative Lindblad terms and dephasing is analyzed, and all the parameters...
Femtosecond Non-Markovian Optical Dynamics in Solution
Nibbering, Erik T.J.; Wiersma, Douwe A.; Duppen, Koos
1991-01-01
Femtosecond photon-echo experiments on sodium resorufin in dimethylsulfoxide at room temperature show that optical dephasing in solution is of non-Markovian character. A single Gauss-Markov stochastic modulation process is used to interpret both the femtosecond light-scattering results and the
Femtosecond two-dimensional spectroscopy of molecular motion in liquids
Steffen, T; Duppen, K.
1996-01-01
Intermolecular motion in CS2 and benzene is investigated by femtosecond nonresonant four- and six-wave mixing. Impulsive stimulated six-wave mixing yields new information on dephasing of coherent nuclear motion, not accessible from four-wave mixing experiments. The results cannot be modeled by two
Localized excitons in quantum wells show spin relaxation without coherence loss
DEFF Research Database (Denmark)
Zimmermann, R.; Langbein, W.; Runge, E.
2001-01-01
The coherence in the secondary emission from quantum well excitons is studied using the speckle method. Analysing the different polarization channels allows to conclude that (i) no coherence loss occurs in the cross-polarized emission, favouring spin beating instead of spin dephasing, and that (i...
Non-linear wave packet dynamics of coherent states
Indian Academy of Sciences (India)
In recent years, the non-linear quantum dynamics of these states have revealed some striking features. It was found that under the action of a Hamil- tonian which is a non-linear function of the photon operator(s) only, an initial coherent state loses its coherent structure quickly due to quantum dephasing induced by the non-.
Timeresolved Speckle Analysis: Probing the Coherence of Excitonic Secondary Emission
DEFF Research Database (Denmark)
Langbein, Wolfgang; Hvam, Jørn Märcher; Zimmermann, R.
1998-01-01
in semiconductor quantum wells is investigated. Here, a partial coherence results from an interplay between scattering due to static disorder and inelastic relaxation, without any influence of the radiative decay. The temperature dependence is well explained by dephasing due to phonon scattering....
Maintaining quantum coherence in the presence of noise through state monitoring
CSIR Research Space (South Africa)
Konrad, T
2012-01-01
Full Text Available in the presence of classical dephasing and amplitude noise, by simulating such measurements on a two-level system undergoing Rabi oscillations. Finite estimation fidelity is found to persist indefinitely after the decoherence times set by the noise fields...
Modelling exciton–phonon interactions in optically driven quantum dots
DEFF Research Database (Denmark)
Nazir, Ahsan; McCutcheon, Dara
2016-01-01
We provide a self-contained review of master equation approaches to modelling phonon effects in optically driven self-assembled quantum dots. Coupling of the (quasi) two-level excitonic system to phonons leads to dissipation and dephasing, the rates of which depend on the excitation conditions...
Long lived coherence in self-assembled quantum dots
DEFF Research Database (Denmark)
Birkedal, Dan; Leosson, Kristjan; Hvam, Jørn Märcher
2001-01-01
We report measurements of ultralong coherence in self-assembled quantum dots. Transient four-wave mixing experiments at 5 K show an average dephasing time of 372 ps, corresponding to a homogeneous linewidth of 3.5 mu eV, which is significantly smaller than the linewidth observed in single...
Toroidal drift magnetic pumping
International Nuclear Information System (INIS)
Canobbio, E.
1977-01-01
A set of azimuthal coils which carry properly dephased rf-currents in the KHz frequency range can be used to heat toroidal plasmas by perpendicular Landau damping of subsonic Alfven waves. The heating mechanism and the rf-field structure are discussed in some detail
Pramana – Journal of Physics | Indian Academy of Sciences
Indian Academy of Sciences (India)
... and quantum tunneling are presented. Simple analysis of sharp phase jumps observed in double-slit Aharonov–Bohm experiments is given. Some consequences of parity violation are elaborated. Finally, we brieﬂy describe the dephasing of Aharonov–Bohm oscillations in Aharonov–Bohm ring geometry due to spin-ﬂip ...
International Nuclear Information System (INIS)
2006-01-01
This conference was organized around 9 sessions: -) single molecule, -) quantum optics, -) hole-burning materials and mechanisms, -) single nano-particle spectroscopy, -) dephasing and spectral diffusion, -) microwave photonics, -) biological systems, -) rare earth doped materials, -) novel laser sources. This document gathers only the slides of the presentations
DEFF Research Database (Denmark)
Hvam, Jørn Märcher; Langbein, Wolfgang; Borri, Paola
1999-01-01
Coherent optical spectroscopy in the form of nonlinear transient four-wave mixing (TFWM) and linear resonant Rayleigh scattering (RRS) has been applied to investigate the exciton dynamics of low-dimensional semiconductor heterostructures. The dephasing times of excitons are determined from...
Boulesbaa, Abdelaziz; Borguet, Eric
2014-02-06
The dephasing dynamics of a vibrational coherence may reveal the interactions of chemical functional groups with their environment. To investigate this process at a surface, we employ free induction decay sum frequency generation (FID-SFG) to measure the time that it takes for free OH stretch oscillators at the charged (pH ≈ 13, KOH) interface of alumina/water (Al2O3/H2O) to lose their collective coherence. By employing noncollinear optical parametric amplification (NOPA) technology and nonlinear vibrational spectroscopy, we showed that the single free OH peak actually corresponds to two distinct oscillators oriented opposite to each other and measured the total dephasing time, T2, of the free OH stretch modes at the Al2O3/H2O interface with a sub-40 fs temporal resolution. Our results suggested that the free OH oscillators associated with interfacial water dephase on the time scale of 89.4 ± 6.9 fs, whereas the homogeneous dephasing of interfacial alumina hydroxyls is an order of magnitude slower.
DEFF Research Database (Denmark)
Wagner, Hans Peter; Schätz, A.; Maier, R.
1997-01-01
We investigate the dephasing of heavy-hole excitons in different free-standing ZnSxSe1-x/ZnSe layer structures by spectrally resolved transient four-wave mixing. ZnSe layers of 80, 8, and 4 nm thickness with ternary barriers are studied, representing the crossover from quasi-three-dimensional to ...
Transient four-wave mixing in T-shaped GaAs quantum wires
DEFF Research Database (Denmark)
Langbein, Wolfgang Werner; Gislason, Hannes; Hvam, Jørn Märcher
1999-01-01
The binding energy of excitons and biexcitons and the exciton dephasing in T-shaped GaAs quantum wires is investigated by transient four-wave mixing. The T-shaped structure is fabricated by cleaved-edge overgrowth, and its geometry is engineered to optimize the one-dimensional confinement. In thi...
Energy Technology Data Exchange (ETDEWEB)
NONE
2006-07-01
This conference was organized around 9 sessions: -) single molecule, -) quantum optics, -) hole-burning materials and mechanisms, -) single nano-particle spectroscopy, -) dephasing and spectral diffusion, -) microwave photonics, -) biological systems, -) rare earth doped materials, -) novel laser sources. This document gathers only the slides of the presentations.
Physics at the FMQT’08 conference
Špička, V.; Nieuwenhuizen, T.M.; Keefe, P.D.
2010-01-01
This paper summarizes the recent state of the art of the following topics presented at the FQMT’08 conference: Foundations of quantum physics, Quantum measurement; Quantum noise, decoherence and dephasing; Cold atoms and Bose-Einstein condensation; Physics of quantum computing and information;
New Applications of Ultrafast Spectroscopy
DEFF Research Database (Denmark)
Hvam, Jørn Märcher
1999-01-01
Dephasing processes in the optical transitions in low-dimensional semiconductor nanostructures are studied by a novel technique involving a speckle analysis of the secondary emission after a short-pulse resonant excitation. The results are compared with more conventional transient four-wave mixin...
Towards a coherent picture of excitonic coherence in the Fenna–Matthews–Olson complex
International Nuclear Information System (INIS)
Fidler, Andrew F; Caram, Justin R; Hayes, Dugan; Engel, Gregory S
2012-01-01
Observations of long-lived coherence between excited states in several photosynthetic antenna complexes has motivated interest in developing a more detailed understanding of the role of the protein matrix in guiding the underlying dynamics of the system. These experiments suggest that classical rate laws may not provide an adequate description of the energy transfer process and that quantum effects must be taken into account to describe the near unity transfer efficiency in these systems. Recently, it has been shown that coherences between different pairs of excitons dephase at different rates. These details should provide some insight about the underlying electronic structure of the complex and its coupling to the protein bath. Here we show that a simple model can account for the different dephasing rates as well as the most current available experimental evidence of excitonic coherences in the Fenna–Matthews–Olson complex. The differences in dephasing rates can be understood as arising largely from differences in the delocalization and shared character between the underlying electronic states. We also suggest that the anomalously low dephasing rate of the exciton 1–2 coherence is enhanced by non-secular effects. (paper)
Genuinely Multipartite Concurrence of N-qubit X Matrices (Author’s Final Manuscript)
2012-12-05
Horne- Zeilinger (GHZ) states. We study the case when each qubit interacts with a local amplitude damping channel. It is shown that only one type of GHZ...multipartite entanglement that is simple to calculate. Only for Greenberger-Horne- Zeilinger (GHZ) states that undergo pure dephasing, has there been a
Spectral signatures of x((5)) processes in four-wave mixing of homogeneously broadened excitons
DEFF Research Database (Denmark)
Langbein, W.; Meier, T.; Koch, S.W.
2001-01-01
-biexciton beating at the exciton resonance is observed that is vanishing for long negative delays owing to the faster dephasing in the two-exciton continuum compared with the bound biexciton state. These results are in qualitative agreement with microscopic model calculations that include the coherent dynamics...... of one- and two-exciton resonances up to the fifth order in the optical field....
International Nuclear Information System (INIS)
Barwick, Brett; Gronniger, Glen; Yuan, Lu; Liou, Sy-Hwang; Batelaan, Herman
2006-01-01
Electron diffraction from metal coated freestanding nanofabricated gratings is presented, with a quantitative path integral analysis of the electron-grating interactions. Electron diffraction out to the 20th order was observed indicating the high quality of our nanofabricated gratings. The electron beam is collimated to its diffraction limit with ion-milled material slits. Our path integral analysis is first tested against single slit electron diffraction, and then further expanded with the same theoretical approach to describe grating diffraction. Rotation of the grating with respect to the incident electron beam varies the effective distance between the electron and grating bars. This allows the measurement of the image charge potential between the electron and the grating bars. Image charge potentials that were about 15% of the value for that of a pure electron-metal wall interaction were found. We varied the electron energy from 50 to 900 eV. The interaction time is of the order of typical metal image charge response times and in principle allows the investigation of image charge formation. In addition to the image charge interaction there is a dephasing process reducing the transverse coherence length of the electron wave. The dephasing process causes broadening of the diffraction peaks and is consistent with a model that ascribes the dephasing process to microscopic contact potentials. Surface structures with length scales of about 200 nm observed with a scanning tunneling microscope, and dephasing interaction strength typical of contact potentials of 0.35 eV support this claim. Such a dephasing model motivated the investigation of different metallic coatings, in particular Ni, Ti, Al, and different thickness Au-Pd coatings. Improved quality of diffraction patterns was found for Ni. This coating made electron diffraction possible at energies as low as 50 eV. This energy was limited by our electron gun design. These results are particularly relevant for the
Energy Technology Data Exchange (ETDEWEB)
Baker, Lewis A.; Habershon, Scott, E-mail: S.Habershon@warwick.ac.uk [Department of Chemistry and Centre for Scientific Computing, University of Warwick, Coventry CV4 7AL (United Kingdom)
2015-09-14
Pigment-protein complexes (PPCs) play a central role in facilitating excitation energy transfer (EET) from light-harvesting antenna complexes to reaction centres in photosynthetic systems; understanding molecular organisation in these biological networks is key to developing better artificial light-harvesting systems. In this article, we combine quantum-mechanical simulations and a network-based picture of transport to investigate how chromophore organization and protein environment in PPCs impacts on EET efficiency and robustness. In a prototypical PPC model, the Fenna-Matthews-Olson (FMO) complex, we consider the impact on EET efficiency of both disrupting the chromophore network and changing the influence of (local and global) environmental dephasing. Surprisingly, we find a large degree of resilience to changes in both chromophore network and protein environmental dephasing, the extent of which is greater than previously observed; for example, FMO maintains EET when 50% of the constituent chromophores are removed, or when environmental dephasing fluctuations vary over two orders-of-magnitude relative to the in vivo system. We also highlight the fact that the influence of local dephasing can be strongly dependent on the characteristics of the EET network and the initial excitation; for example, initial excitations resulting in rapid coherent decay are generally insensitive to the environment, whereas the incoherent population decay observed following excitation at weakly coupled chromophores demonstrates a more pronounced dependence on dephasing rate as a result of the greater possibility of local exciton trapping. Finally, we show that the FMO electronic Hamiltonian is not particularly optimised for EET; instead, it is just one of many possible chromophore organisations which demonstrate a good level of EET transport efficiency following excitation at different chromophores. Overall, these robustness and efficiency characteristics are attributed to the highly
International Nuclear Information System (INIS)
McGuire, John Andrew
2004-01-01
The high temporal resolution and broad bandwidth of a femtosecond laser system are exploited in a pair of nonlinear optical studies of surfaces. The dephasing dynamics of resonances associated with the adatom dangling bonds of the Si(111)7 x 7 surface are explored by transient second-harmonic hole burning, a process that can be described as a fourth-order nonlinear optical process. Spectral holes produced by a 100 fs pump pulse at about 800 nm are probed by the second harmonic signal of a 100 fs pulse tunable around 800 nm. The measured spectral holes yield homogeneous dephasing times of a few tens of femtoseconds. Fits with a Lorentzian spectral hole centered at zero probe detuning show a linear dependence of the hole width on pump fluence, which suggests that charge carrier-carrier scattering dominates the dephasing dynamics at the measured excitation densities. Extrapolation of the deduced homogeneous dephasing times to zero excitation density yields an intrinsic dephasing time of ∼ 70 fs. The presence of a secondary spectral hole indicates that scattering of the surface electrons with surface optical phonons at 570 cm -1 occurs within the first 200 fs after excitation. The broad bandwidth of femtosecond IR pulses is used to perform IR-visible sum frequency vibrational spectroscopy. By implementing a Fourier-transform technique, we demonstrate the ability to obtain sub-laser-bandwidth spectral resolution. FT-SFG yields a greater signal when implemented with a stretched visible pulse than with a femtosecond visible pulse. However, when compared with multichannel spectroscopy using a femtosecond IR pulse but a narrowband visible pulse, Fourier-transform SFG is found to have an inferior signal-to-noise ratio. A mathematical analysis of the signal-to-noise ratio illustrates the constraints on the Fourier-transform approach
International Nuclear Information System (INIS)
Baker, Lewis A.; Habershon, Scott
2015-01-01
Pigment-protein complexes (PPCs) play a central role in facilitating excitation energy transfer (EET) from light-harvesting antenna complexes to reaction centres in photosynthetic systems; understanding molecular organisation in these biological networks is key to developing better artificial light-harvesting systems. In this article, we combine quantum-mechanical simulations and a network-based picture of transport to investigate how chromophore organization and protein environment in PPCs impacts on EET efficiency and robustness. In a prototypical PPC model, the Fenna-Matthews-Olson (FMO) complex, we consider the impact on EET efficiency of both disrupting the chromophore network and changing the influence of (local and global) environmental dephasing. Surprisingly, we find a large degree of resilience to changes in both chromophore network and protein environmental dephasing, the extent of which is greater than previously observed; for example, FMO maintains EET when 50% of the constituent chromophores are removed, or when environmental dephasing fluctuations vary over two orders-of-magnitude relative to the in vivo system. We also highlight the fact that the influence of local dephasing can be strongly dependent on the characteristics of the EET network and the initial excitation; for example, initial excitations resulting in rapid coherent decay are generally insensitive to the environment, whereas the incoherent population decay observed following excitation at weakly coupled chromophores demonstrates a more pronounced dependence on dephasing rate as a result of the greater possibility of local exciton trapping. Finally, we show that the FMO electronic Hamiltonian is not particularly optimised for EET; instead, it is just one of many possible chromophore organisations which demonstrate a good level of EET transport efficiency following excitation at different chromophores. Overall, these robustness and efficiency characteristics are attributed to the highly
Energy Technology Data Exchange (ETDEWEB)
McGuire, John Andrew [Univ. of California, Berkeley, CA (United States)
2004-11-24
The high temporal resolution and broad bandwidth of a femtosecond laser system are exploited in a pair of nonlinear optical studies of surfaces. The dephasing dynamics of resonances associated with the adatom dangling bonds of the Si(111)7 x 7 surface are explored by transient second-harmonic hole burning, a process that can be described as a fourth-order nonlinear optical process. Spectral holes produced by a 100 fs pump pulse at about 800 nm are probed by the second harmonic signal of a 100 fs pulse tunable around 800 nm. The measured spectral holes yield homogeneous dephasing times of a few tens of femtoseconds. Fits with a Lorentzian spectral hole centered at zero probe detuning show a linear dependence of the hole width on pump fluence, which suggests that charge carrier-carrier scattering dominates the dephasing dynamics at the measured excitation densities. Extrapolation of the deduced homogeneous dephasing times to zero excitation density yields an intrinsic dephasing time of {approx} 70 fs. The presence of a secondary spectral hole indicates that scattering of the surface electrons with surface optical phonons at 570 cm^{-1} occurs within the first 200 fs after excitation. The broad bandwidth of femtosecond IR pulses is used to perform IR-visible sum frequency vibrational spectroscopy. By implementing a Fourier-transform technique, we demonstrate the ability to obtain sub-laser-bandwidth spectral resolution. FT-SFG yields a greater signal when implemented with a stretched visible pulse than with a femtosecond visible pulse. However, when compared with multichannel spectroscopy using a femtosecond IR pulse but a narrowband visible pulse, Fourier-transform SFG is found to have an inferior signal-to-noise ratio. A mathematical analysis of the signal-to-noise ratio illustrates the constraints on the Fourier-transform approach.
Random unitary operations and quantum Darwinism
International Nuclear Information System (INIS)
Balaneskovic, Nenad
2016-01-01
We study the behavior of Quantum Darwinism (Zurek, Nature Physics 5, 181-188 (2009)) within the iterative, random unitary operations qubit-model of pure decoherence (Novotn'y et al, New Jour. Phys. 13, 053052 (2011)). We conclude that Quantum Darwinism, which describes the quantum mechanical evolution of an open system from the point of view of its environment, is not a generic phenomenon, but depends on the specific form of initial states and on the type of system-environment interactions. Furthermore, we show that within the random unitary model the concept of Quantum Darwinism enables one to explicitly construct and specify artificial initial states of environment that allow to store information about an open system of interest and its pointer-basis with maximal efficiency. Furthermore, we investigate the behavior of Quantum Darwinism after introducing dissipation into the iterative random unitary qubit model with pure decoherence in accord with V. Scarani et al (Phys. Rev. Lett. 88, 097905 (2002)) and reconstruct the corresponding dissipative attractor space. We conclude that in Zurek's qubit model Quantum Darwinism depends on the order in which pure decoherence and dissipation act upon an initial state of the entire system. We show explicitly that introducing dissipation into the random unitary evolution model in general suppresses Quantum Darwinism (regardless of the order in which decoherence and dissipation are applied) for all positive non-zero values of the dissipation strength parameter, even for those initial state configurations which, in Zurek's qubit model and in the random unitary model with pure decoherence, would lead to Quantum Darwinism. Finally, we discuss what happens with Quantum Darwinism after introducing into the iterative random unitary qubit model with pure decoherence (asymmetric) dissipation and dephasing, again in accord with V. Scarani et al (Phys. Rev. Lett. 88, 097905 (2002)), and reconstruct the corresponding
Joo, Taiha
Ultrafast molecular processes in the condensed phase at room temperature are studied in the time domain by four wave mixing spectroscopy. The structure/dynamics of various quantum states can be studied by varying the time ordering of the incident fields, their polarization, their colors, etc. In one, time-resolved coherent Stokes Raman spectroscopy of benzene is investigated at room temperature. The reorientational correlation time of benzene as well as the T_2 time of the nu _1 ring-breathing mode have been measured by using two different polarization geometries. Bohr frequency difference beats have also been resolved between the nu_1 modes of ^ {12}C_6H_6 and ^{12}C_5^{13 }CH_6.. The dephasing dynamics of the nu _1 ring-breathing mode of neat benzene is studied by time-resolved coherent anti-Stokes Raman scattering. Ultrafast time resolution reveals deviation from the conventional exponential decay. The correlation time, tau _{rm c}, and the rms magnitude, Delta, of the Bohr frequency modulation are determined for the process responsible for the vibrational dephasing by Kubo dephasing function analysis. The electronic dephasing of two oxazine dyes in ethylene glycol at room temperature is investigated by photon echo experiments. It was found that at least two stochastic processes are responsible for the observed electronic dephasing. Both fast (homogeneous) and slow (inhomogeneous) dynamics are recovered using Kubo line shape analysis. Moreover, the slow dynamics is found to spectrally diffuse over the inhomogeneous distribution on the time scale around a picosecond. Time-resolved degenerate four wave mixing signal of dyes in a population measurement geometry is reported. The vibrational coherences both in the ground and excited electronic states produced strong oscillations in the signal together with the usual population decay from the excited electronic state. Absolute frequencies and their dephasing times of the vibrational modes at ~590 cm^{-1} are obtained
High-order noise filtering in nontrivial quantum logic gates.
Green, Todd; Uys, Hermann; Biercuk, Michael J
2012-07-13
Treating the effects of a time-dependent classical dephasing environment during quantum logic operations poses a theoretical challenge, as the application of noncommuting control operations gives rise to both dephasing and depolarization errors that must be accounted for in order to understand total average error rates. We develop a treatment based on effective Hamiltonian theory that allows us to efficiently model the effect of classical noise on nontrivial single-bit quantum logic operations composed of arbitrary control sequences. We present a general method to calculate the ensemble-averaged entanglement fidelity to arbitrary order in terms of noise filter functions, and provide explicit expressions to fourth order in the noise strength. In the weak noise limit we derive explicit filter functions for a broad class of piecewise-constant control sequences, and use them to study the performance of dynamically corrected gates, yielding good agreement with brute-force numerics.
Time-domain vibrational study on defects in ion-irradiated crystal
International Nuclear Information System (INIS)
Kitajima, M.
2003-01-01
We have studied the effects of point defects on coherent phonons in ion-implanted bismuth and graphite. Ultrafast dynamics of coherent phonons and photo-generated carriers in the femtosecond time-domain have been investigated by means of pump-probe reflectivity measurements. Point defects are introduced by irradiating graphite with 5 keV He + ions. For Bi the dephasing rate of the A 1g phonon increases linearly with increasing ion dose, which is explained by the additional dephasing process of the coherent phonon originated from scattering of phonons by the defects. For graphite, introduction of the defects enhances the carrier relaxation by opening a decay channel via vacancy-states, which competes efficiently with carrier-phonon scattering. The coherent acoustic phonon relaxation is also accelerated due to an additional scattering by defects. The linear fluence-dependence of the decay rate is understood as scattering of propagating acoustic phonon by single vacancies. (author)
Contrast-enhanced MR angiography
International Nuclear Information System (INIS)
Bosmans, H.; Marchal, G.
1996-01-01
Despite many optimizations, the current limitations of plain MR angiography include: Saturation that impairs the visualization of veins and arteries with slow flow and spin-dephasing signal voids in locations with turbulent flow. Recently, the use of contrast agents has been proposed to cope with these remaining problems. Because of induced shortening of the T1 of the blood, saturation in the blood vessels is overcome. As a result, arteries and veins are visualized with the same signal intensity, which makes the technique less flow-dependent. In combination with short T1-weighted acquisitions, today CE MRA can be obtained while the patient is holding his breath. This last approach is most promising for abdominal applications since the respiratory motion can be frozen. As these acquisitions also use very short echo times, spin dephasing can be reduced. In conclusion, the use of contrast agents has greatly increased the clinical usefulness of MR angiography. (orig.) [de
Spin noise spectroscopy of donor-bound electrons in ZnO
Horn, H.; Balocchi, A.; Marie, X.; Bakin, A.; Waag, A.; Oestreich, M.; Hübner, J.
2013-01-01
We investigate the intrinsic spin dynamics of electrons bound to Al impurities in bulk ZnO by optical spin noise spectroscopy. Spin noise spectroscopy enables us to investigate the longitudinal and transverse spin relaxation time with respect to nuclear and external magnetic fields in a single spectrum. On one hand, the spin dynamic is dominated by the intrinsic hyperfine interaction with the nuclear spins of the naturally occurring 67Zn isotope. We measure a typical spin dephasing time of 23 ns, in agreement with the expected theoretical values. On the other hand, we measure a third, very high spin dephasing rate which is attributed to a high defect density of the investigated ZnO material. Measurements of the spin dynamics under the influence of transverse as well as longitudinal external magnetic fields unambiguously reveal the intriguing connections of the electron spin with its nuclear and structural environment.
Tightness Entropic Uncertainty Relation in Quantum Markovian-Davies Environment
Zhang, Jun; Liu, Liang; Han, Yan
2018-05-01
In this paper, we investigate the tightness of entropic uncertainty relation in the absence (presence) of the quantum memory which the memory particle being weakly coupled to a decohering Davies-type Markovian environment. The results show that the tightness of the quantum uncertainty relation can be controlled by the energy relaxation time F, the dephasing time G and the rescaled temperature p, the perfect tightness can be arrived by dephasing and energy relaxation satisfying F = 2G and p = 1/2. In addition, the tightness of the memory-assisted entropic uncertainty relation and the entropic uncertainty relation can be influenced mainly by the purity. While in memory-assisted model, the purity and quantum correlation can also influence the tightness actively while the quantum entanglement can influence the tightness slightly.
Low-field magnetotransport in graphene cavity devices
Zhang, G. Q.; Kang, N.; Li, J. Y.; Lin, Li; Peng, Hailin; Liu, Zhongfan; Xu, H. Q.
2018-05-01
Confinement and edge structures are known to play significant roles in the electronic and transport properties of two-dimensional materials. Here, we report on low-temperature magnetotransport measurements of lithographically patterned graphene cavity nanodevices. It is found that the evolution of the low-field magnetoconductance characteristics with varying carrier density exhibits different behaviors in graphene cavity and bulk graphene devices. In the graphene cavity devices, we observed that intravalley scattering becomes dominant as the Fermi level gets close to the Dirac point. We associate this enhanced intravalley scattering to the effect of charge inhomogeneities and edge disorder in the confined graphene nanostructures. We also observed that the dephasing rate of carriers in the cavity devices follows a parabolic temperature dependence, indicating that the direct Coulomb interaction scattering mechanism governs the dephasing at low temperatures. Our results demonstrate the importance of confinement in carrier transport in graphene nanostructure devices.
Coherence in a transmon qubit with epitaxial tunnel junctions
Energy Technology Data Exchange (ETDEWEB)
Weides, Martin [National Institute of Standards and Technology, Boulder, Colorado 80305 (United States); Karlsruhe Institute of Technology (Germany); Kline, Jeffrey; Vissers, Michael; Sandberg, Martin; Pappas, David [National Institute of Standards and Technology, Boulder, Colorado 80305 (United States); Wisbey, David [National Institute of Standards and Technology, Boulder, Colorado 80305 (United States); Saint Louis University, St. Louis, Missouri 63103 (United States); Johnson, Blake; Ohki, Thomas [Raytheon BBN Technologies, Cambridge, Massachusetts 02138 (United States)
2012-07-01
Transmon qubits based on epitaxial tunnel junctions and interdigitated capacitors were developed. This multileveled qubit, patterned by use of all-optical lithography, is a step towards scalable qubits with a high integration density. The relaxation time T{sub 1} is.72-.86 {mu} sec and the ensemble dephasing time T{sub 2}{sup *} is slightly larger than T{sub 1}. The dephasing time T{sub 2} (1.36 {mu} sec) is nearly energy-relaxation-limited. Qubit spectroscopy yields weaker level splitting than observed in qubits with amorphous barriers in equivalent-size junctions. The qubit's inferred microwave loss closely matches the weighted losses of the individual elements (junction, wiring dielectric, and interdigitated capacitor), determined by independent resonator measurements.
System–environment correlations and non-Markovian dynamics
International Nuclear Information System (INIS)
Pernice, A; Helm, J; Strunz, W T
2012-01-01
We determine the total state dynamics of a dephasing open quantum system using the standard environment of harmonic oscillators. Of particular interest are random unitary approaches to the same reduced dynamics and system–environment correlations in the full model. Concentrating on a model with an at times negative dephasing rate, the issue of ‘non-Markovianity’ will also be addressed. Crucially, given the quantum environment, the appearance of non-Markovian dynamics turns out to be accompanied by a loss of system–environment correlations. Depending on the initial purity of the qubit state, these system–environment correlations may be purely classical over the whole relevant time scale, or there may be intervals of genuine system–environment entanglement. In the latter case, we see no obvious relation between the build-up or decay of these quantum correlations and ‘non-Markovianity’. (paper)
A diffusive thermal phase shifter; Dephaseur thermique diffusif
Energy Technology Data Exchange (ETDEWEB)
Lachal, B; Hollmuller, P; Zgraggen, J -M [Universite de Geneve, Centre universitaire d' etude des problemes de l' energie(CUEPE), Geneva (Switzerland)
2004-07-01
The investigations carried out in this project show that dephasing a thermal oscillation carried by an air flow by utilizing the heat exchange with a diffusive heat store made of thin layers, is possible without any significant damping of the oscillation. The practical application of this phenomenon, with a time shift of 8 to 12 hours, looks particularly attractive for space cooling of buildings during summertime or in hot climates. The possibilities of dephasing completely a thermal wave (i.e. by a half period) carried by a stream of air have been investigated both theoretically by model calculations and experimentally by building two prototypes. Promising results have been obtained for the case of a daily phase shift. In the case of a summer-winter shift the required volumes and lengths seem too large to enable such a storage system becoming cost effective.
Dynamics of a Landau-Zener transitions in a two-level system driven by a dissipative environment
Ateuafack, M. E.; Diffo, J. T.; Fai, L. C.
2016-02-01
The paper investigates the effects of a two-level quantum system coupled to transversal and longitudinal dissipative environment. The time-dependent phase accumulation, LZ transition probability and entropy in the presence of fast-ohmic, sub-ohmic and super-ohmic quantum noise are derived. Analytical results are obtained in terms of temperature, dissipation strength, LZ parameter and bath cutoff frequency. The bath is observed to modify the standard occupation difference by a decaying random phase factor and also produces dephasing during the transfer of population. The dephasing characteristics or the initial non-zero decoherence rate are observed to increase in time with the bath temperature and depend on the system-bath coupling strength and cutoff frequency. These parameters are found to strongly affect the memory and thus tailor the coherence process of the system.
Dynamics of a Landau–Zener transitions in a two-level system driven by a dissipative environment
Energy Technology Data Exchange (ETDEWEB)
Ateuafack, M.E., E-mail: esouamath@yahoo.fr [Mesoscopic and Multilayer Structures Laboratory, Department of Physics, Faculty of Science, University of Dschang (Cameroon); Diffo, J.T., E-mail: diffojaures@yahoo.com [Mesoscopic and Multilayer Structures Laboratory, Department of Physics, Faculty of Science, University of Dschang (Cameroon); Department of Physics, Higher Teachers' Training College, The University of Maroua, PO Box 55 Maroua (Cameroon); Fai, L.C., E-mail: corneliusfai@yahoo.fr [Mesoscopic and Multilayer Structures Laboratory, Department of Physics, Faculty of Science, University of Dschang (Cameroon)
2016-02-15
The paper investigates the effects of a two-level quantum system coupled to transversal and longitudinal dissipative environment. The time-dependent phase accumulation, LZ transition probability and entropy in the presence of fast-ohmic, sub-ohmic and super-ohmic quantum noise are derived. Analytical results are obtained in terms of temperature, dissipation strength, LZ parameter and bath cutoff frequency. The bath is observed to modify the standard occupation difference by a decaying random phase factor and also produces dephasing during the transfer of population. The dephasing characteristics or the initial non-zero decoherence rate are observed to increase in time with the bath temperature and depend on the system-bath coupling strength and cutoff frequency. These parameters are found to strongly affect the memory and thus tailor the coherence process of the system.
Progress and Perspectives of Plasmon-Enhanced Solar Energy Conversion.
Cushing, Scott K; Wu, Nianqiang
2016-02-18
Plasmonics allows extraordinary control of light, making it attractive for application in solar energy harvesting. In metal-semiconductor heterojunctions, plasmons can enhance photoconversion in the semiconductor via three mechanisms, including light trapping, hot electron/hole transfer, and plasmon-induced resonance energy transfer (PIRET). To understand the plasmonic enhancement, the metal's geometry, constituent metal, and interface must be viewed in terms of the effects on the plasmon's dephasing and decay route. To simplify design of plasmonic metal-semiconductor heterojunctions for high-efficiency solar energy conversion, the parameters controlling the plasmonic enhancement can be distilled to the dephasing time. The plasmonic geometry can then be further refined to optimize hot carrier transfer, PIRET, or light trapping.
Decoherence of coupled Josephson charge qubits due to partially correlated low-frequency noise
International Nuclear Information System (INIS)
Hu, Yong; Zhou, Zheng-Wei; Cai, Jian-Ming; Guo, Guang-Can
2007-01-01
Josephson charge qubits are promising candidates for scalable quantum computing. However, their performances are strongly degraded by decoherence due to low-frequency background noise, typically with a 1/f spectrum. In this paper, we investigate the decoherence process of two Cooper pair boxes (CPBs) coupled via a capacitor. Going beyond the common and uncorrelated noise models and the Bloch-Redfield formalism of previous works, we study the coupled system's quadratic dephasing under the condition of partially correlated noise sources. Based on reported experiments and generally accepted noise mechanisms, we introduce a reasonable assumption for the noise correlation, with which the calculation of multiqubit decoherence can be simplified to a problem on the single-qubit level. For the conventional Gaussian 1/f noise case, our results demonstrate that the quadratic dephasing rates are not very sensitive to the spatial correlation of the noises. Furthermore, we discuss the feasibility and efficiency of dynamical decoupling in the coupled CPBs
Synchronization of diffusively coupled oscillators near the homoclinic bifurcation
International Nuclear Information System (INIS)
Postnov, D.; Han, Seung Kee; Kook, Hyungtae
1998-09-01
It has been known that a diffusive coupling between two limit cycle oscillations typically leads to the inphase synchronization and also that it is the only stable state in the weak coupling limit. Recently, however, it has been shown that the coupling of the same nature can result in the distinctive dephased synchronization when the limit cycles are close to the homoclinic bifurcation, which often occurs especially for the neuronal oscillators. In this paper we propose a simple physical model using the modified van der Pol equation, which unfolds the generic synchronization behaviors of the latter kind and in which one may readily observe changes in the synchronization behaviors between the distinctive regimes as well. The dephasing mechanism is analyzed both qualitatively and quantitatively in the weak coupling limit. A general form of coupling is introduced and the synchronization behaviors over a wide range of the coupling parameters are explored to construct the phase diagram using the bifurcation analysis. (author)
International Nuclear Information System (INIS)
Xiang Shaohua; Deng Xiaopeng; Song Kehui; Wen Wei; Shi Zhengang
2011-01-01
We investigate the entanglement dynamics of two electron-spin qubits in the quantum-dot (QD)-microcavity system in the large-detuning limit and subjected to two different noise sources: electron-spin dephasing and relaxation. We show that when one of the two dots is prepared initially in the excited state, the created entanglement exhibits oscillatory behavior at the beginning of evolution and then completely disappears over time. For two QDs that are initially in either the Einstein-Podolsky-Rosen-Bell states or the Werner states, their entanglement evolution exhibits the same behavior in the presence of pure dephasing, but is completely different under the relaxation process. We also show that the interdot interaction induced by a single-mode cavity field does not contribute to the dynamics of entanglement for these Bell states and Werner states.
Quantum interference in the system of Lorentzian and Fano magnetoexciton resonances in GaAs
International Nuclear Information System (INIS)
Siegner, U.; Mycek, M.; Glutsch, S.; Chemla, D.S.
1995-01-01
Using femtosecond four-wave mixing (FWM), we study the coherent dynamics of Lorentzian and Fano magnetoexciton resonances in GaAs. For unperturbed Lorentzian magnetoexcitons, we find that the time-integrated FWM signal decays due to dephasing processes as expected for Lorentzian resonances. The time-integrated FWM signal from a single Fano magnetoexciton resonance, however, decays quasi-instantaneously although the dephasing time of the Fano resonance is much longer than the time resolution of the experiment. This fast decay is the manifestation of destructive quantum interference. Although destructive quantum interference in our system is closely related to the dynamics of Fano resonances, for the simultaneous excitation of Lorentzian and Fano magnetoexciton resonances destructive quantum interference also strongly affects the dynamics of Lorentzian magnetoexcitons due to quantum-mechanical coupling between the two types of resonances
Zhang, Xu; Chen, Ye-Hong; Shi, Zhi-Cheng; Shan, Wu-Jiang; Song, Jie; Xia, Yan
2017-12-01
Combining the advantages of the dressed states and superconducting quantum interference device (SQUID) qubits, we propose an efficient scheme to generate Greenberger-Horne-Zeilinger (GHZ) states for three SQUID qubits. Firstly, we elaborate how to generate GHZ states of three SQUID qubits by choosing a set of dressed states suitably. Then, we compare the scheme by using dressed states with that via the adiabatic passage. Lastly, the influence of various decoherence factors, such as cavity decay, spontaneous emission and dephasing, is analyzed numerically. All of the results show that the GHZ state can be obtained fast and with high fidelity and that the present scheme is robust against the cavity decay and spontaneous emission. In addition, our scheme is more stable against the dephasing than the adiabatic scheme.
International Nuclear Information System (INIS)
Chang Yan; Zhang Shi-Bin; Yan Li-Li; Han Gui-Hua
2015-01-01
Higher channel capacity and security are difficult to reach in a noisy channel. The loss of photons and the distortion of the qubit state are caused by noise. To solve these problems, in our study, a hyperentangled Bell state is used to design faithful deterministic secure quantum communication and authentication protocol over collective-rotation and collective-dephasing noisy channel, which doubles the channel capacity compared with using an ordinary Bell state as a carrier; a logical hyperentangled Bell state immune to collective-rotation and collective-dephasing noise is constructed. The secret message is divided into several parts to transmit, however the identity strings of Alice and Bob are reused. Unitary operations are not used. (paper)
MRI Artifacts of a Metallic Stent Derived From a Human Aorta Specimen
International Nuclear Information System (INIS)
Soto, M. E.; Flores, P.; Marrufo, O.; Hidalgo, S. S.; Rodriguez, A. O.
2010-01-01
Magnetic resonance imaging has proved to be a useful technique to get images of the whole body. However, the presence of ferromagnetic material can cause susceptibility artifacts, which result from microscopic gradients that occur near the boundaries between areas displaying different magnetic susceptibility. These gradients cause dephasing of spins and frequency shifts in the surrounding tissues. Intravoxel dephasing and spatial mis-registration can degrade image quality. An aorta with a metallic stent was preserved in formaldehyde at 10% inside acrylic cylinders and used to obtain MR images. We tested pulsed spin echo and gradient echo sequences to improve image quality. All experiments were performed on a 7T/21 cm Varian system (Varian, Inc, Palo Alto, CA) equipped with Direct Drive technology and a 16-rung birdcage coil transceiver. The presence of metallic stents produces a lack of signal that might give falsely reassuring appearances within the vessel lumen.
Individual magnetization reversal of a square dot matrix by common current excitation
International Nuclear Information System (INIS)
Elyasi, Mehrdad; Bhatia, Charanjit S; Yang, Hyunsoo
2015-01-01
We have proposed a method for magnetization reversal of individual sites of a 2 by 2 matrix of perpendicularly magnetized dots by common current excitation. The spin-polarized current signal consists of a dc-biased ac part followed by a pure dc one. The amplitude of the dc and ac parts of the current, as well as the phase and duration of the ac current, determine the reversal sites through the magnetostatic interaction among the dots. We show that the individual selectivity in magnetization reversal occurs through two consecutive steps, dephasing of the matrix dyadic pairs dynamics followed by nonlinear dephasing of the individual elements. This method can be utilized to increase the storage density of magnetic random access memory by enabling common access for four or more bits. (paper)
Surface Loving and Surface Avoiding modes
Combe, Nicolas; Huntzinger, Jean Roch; Morillo, Joseph
2008-01-01
International audience; We theoretically study the propagation of sound waves in GaAs/AlAs superlattices focussing on periodic modes in the vicinity of the band gaps. Based on analytical and numerical calculations, we show that these modes are the product of a quickly oscillating function times a slowly varying envelope function. We carefully study the phase of the envelope function compared to the surface of a semi-infinite superlattice. Especially, the dephasing of the superlattice compared...
Fast ultrasonic visualisation under sodium. Application to the fast neutron reactors
International Nuclear Information System (INIS)
Imbert, Ch.
1997-01-01
The fast ultrasonic visualization under sodium is in the programme of research and development on the inspection inside the fast neutron reactors. This work is about the development of a such system of fast ultrasonic imaging under sodium, in order to improve the existing visualization systems. This system is based on the principle of orthogonal imaging, it uses two linear antennas with an important dephasing having 128 piezo-composite elements of central frequency equal to 1.6 MHz. (N.C.)
Energy Technology Data Exchange (ETDEWEB)
Sfihi, H.; Tougne, P.; Legrand, A.P.; Couderc, P.; Saint-Romain, J.L.
1988-12-01
The objective of this paper is to determine structural parameters (aromaticity factor, fractions of protonated and non-protonated aromatic carbons) of some pitches, and to follow their evolution as a function of the heat treatment duration. For such a determination, /sup 13/C-/sup 1/H cross polarization combined with magic angle spinning and dipolar dephasing (CP/MAS/DD) NMR was used. 15 refs., 4 figs., 1 tab.
Annual report of the Applied Optics Laboratory, 1985
International Nuclear Information System (INIS)
1986-01-01
Research on optical fiber coupling by evanescent fields; fiber optics resonators; infrared lasers; remote measurement by laser; dephasing time in GaAs; heat transfer in thin silicon films; quantum wells; a picosecond electron source; modeling of III-V semiconductors; nonlinear optics properties of materials; femtosecond spectroscopy of the internal dynamics of proteins; computer simulation of protein dynamics; electron solvation; reactions of radicals in micella phase; sarcoma; and medical applications of pulsed lasers is presented [fr
Static harmonization of dynamically harmonized Fourier transform ion cyclotron resonance cell.
Zhdanova, Ekaterina; Kostyukevich, Yury; Nikolaev, Eugene
2017-08-01
Static harmonization in the Fourier transform ion cyclotron resonance cell improves the resolving power of the cell and prevents dephasing of the ion cloud in the case of any trajectory of the charged particle, not necessarily axisymmetric cyclotron (as opposed to dynamic harmonization). We reveal that the Fourier transform ion cyclotron resonance cell with dynamic harmonization (paracell) is proved to be statically harmonized. The volume of the statically harmonized potential distribution increases with an increase in the number of trap segments.
Energy Technology Data Exchange (ETDEWEB)
Imbert, Ch
1997-05-30
The fast ultrasonic visualization under sodium is in the programme of research and development on the inspection inside the fast neutron reactors. This work is about the development of a such system of fast ultrasonic imaging under sodium, in order to improve the existing visualization systems. This system is based on the principle of orthogonal imaging, it uses two linear antennas with an important dephasing having 128 piezo-composite elements of central frequency equal to 1.6 MHz. (N.C.)
Energy Technology Data Exchange (ETDEWEB)
Wilson, M A; Hatcher, P G
1988-01-01
Bark samples isolated from brown coal deposits in Victoria, Australia, and buried wood from Rhizophora mangle have been studied by high-resolution solid-state nuclear magnetic resonance (NMR) techniques. Dipolar dephasing /sup 13/C NMR appears to be a useful method of detecting the presence of tannins in geochemical samples including barks, buried woods, peats and leaf litter. It is shown that tannins are selectively preserved in bark during coalification to the brown coal stage. 28 refs., 9 figs., 1 tab.
Wilson, M.A.; Hatcher, P.G.
1988-01-01
Bark samples isolated from brown coal deposits in Victoria, Australia, and buried wood from Rhizophora mangle have been studies by high-resolution solid-state nuclear magnetic resonance (NMR) techniques. Dipolar dephasing 13C NMR appears to be a useful method of detecting the presence of tannins in geochemical samples including barks, buried woods, peats and leaf litter. It is shown that tannins are selectively preserved in bark during coalification to the brown coal stage. ?? 1988.
Random resistor network model of minimal conductivity in graphene.
Cheianov, Vadim V; Fal'ko, Vladimir I; Altshuler, Boris L; Aleiner, Igor L
2007-10-26
Transport in undoped graphene is related to percolating current patterns in the networks of n- and p-type regions reflecting the strong bipolar charge density fluctuations. Finite transparency of the p-n junctions is vital in establishing the macroscopic conductivity. We propose a random resistor network model to analyze scaling dependencies of the conductance on the doping and disorder, the quantum magnetoresistance and the corresponding dephasing rate.
Wüst, Gunter Johannes
2015-01-01
Self-assembled semiconductor quantum dots (QD) are excellent single photon sources and possible hosts for electron spin qubits, which can be initialized, manipulated and read-out optically. The nuclear spins in nano-structured semiconductors play a central role in quantum applications. The nuclear spins represent a useful resource for generating local magnetic fields but nuclear spin noise represents a major source of dephasing for spin qubits. Controlling the nuclear spins enhances the resou...
Pramanik, S.; bandyopadhyay, S.; Cahay, M.
2003-01-01
We study high-field spin transport of electrons in a quasi one-dimensional channel of a $GaAs$ gate controlled spin interferometer (SPINFET) using a semiclassical formalism (spin density matrix evolution coupled with Boltzmann transport equation). Spin dephasing (or depolarization) is predominantly caused by D'yakonov-Perel' relaxation associated with momentum dependent spin orbit coupling effects that arise due to bulk inversion asymmetry (Dresselhaus spin orbit coupling) and structural inve...
Chirp effects on impulsive vibrational spectroscopy: a multimode perspective.
Wand, Amir; Kallush, Shimshon; Shoshanim, Ofir; Bismuth, Oshrat; Kosloff, Ronnie; Ruhman, Sanford
2010-03-07
The well-documented propensity of negatively-chirped pulses to enhance resonant impulsive Raman scattering has been rationalized in terms of a one pulse pump-dump sequence which "follows" the evolution of the excited molecules and dumps them back at highly displaced configurations. The aim of this study was to extend the understanding of this effect to molecules with many displaced vibrational modes in the presence of condensed surroundings. In particular, to define an optimally chirped pulse, to investigate what exactly it "follows" and to discover how this depends on the molecule under study. To this end, linear chirp effects on vibrational coherences in poly-atomics are investigated experimentally and theoretically. Chirped pump-impulsive probe experiments are reported for Sulforhodamine-B ("Kiton Red"), Betaine-30 and Oxazine-1 in ethanol solutions with <10 fs resolution. Numerical simulations, including numerous displaced modes and electronic dephasing, are conducted to reproduce experimental results. Through semi-quantitative reproduction of experimental results in all three systems we show that the effect of group velocity dispersion (GVD) on the buildup of ground state wave-packets depends on the pulse spectrum, on the displacements of vibrational modes upon excitation, on the detuning of the excitation pulses from resonance, and on electronic dephasing rates. Akin to scenarios described for frequency-domain resonance Raman, within the small-displacement regime each mode responds to excitation chirp independently and the optimal GVD is mode-specific. Highly-displaced modes entangle the dynamics of excitation in different modes, requiring a multi-dimensional description of the response. Rapid photochemistry and ultrafast electronic dephasing narrow the window of opportunity for coherent manipulations, leading to a reduced and similar optimal chirp for different modes. Finally, non-intuitive coherent aspects of chirp "following" are predicted in the small
A graphical simulator for teaching basic and advanced MR imaging techniques
DEFF Research Database (Denmark)
Hanson, Lars G
2007-01-01
Teaching of magnetic resonance (MR) imaging techniques typically involves considerable handwaving, literally, to explain concepts such as resonance, rotating frames, dephasing, refocusing, sequences, and imaging. A proper understanding of MR contrast and imaging techniques is crucial for radiolog...... be visualized in an intuitive way. The cross-platform software is primarily designed for use in lectures, but is also useful for self studies and student assignments. Movies available at http://radiographics.rsnajnls.org/cgi/content/full/e27/DC1 ....
Full counting statistics of level renormalization in electron transport through double quantum dots
International Nuclear Information System (INIS)
Luo Junyan; Shen Yu; Cen Gang; He Xiaoling; Wang Changrong; Jiao Hujun
2011-01-01
We examine the full counting statistics of electron transport through double quantum dots coupled in series, with particular attention being paid to the unique features originating from level renormalization. It is clearly illustrated that the energy renormalization gives rise to a dynamic charge blockade mechanism, which eventually results in super-Poissonian noise. Coupling of the double dots to an external heat bath leads to dephasing and relaxation mechanisms, which are demonstrated to suppress the noise in a unique way.
Decoherence and quantum measurements
Namiki, Mikio; Pascazio, Saverio
1997-01-01
The quantum measurement problem is one of the most fascinating and challenging topics in physics both theoretically and experimentally. It involves deep questions and the use of very sophisticated and elegant techniques. After analyzing the fundamental principles of quantum mechanics and of the Copenhagen interpretation, this book reviews the most important approaches to the measurement problem and rigorously reformulates the "collapse of the wave function" by measurement, as a dephasing process quantitatively characterized by an order parameter (called the decoherence parameter), according to
Annual report of the Applied Optics Laboratory, 1986
International Nuclear Information System (INIS)
1987-01-01
Research on optical fiber coupling by evanescent fields; fiber optics resonators; infrared lasers; remote measurement by laser; dephasing time in GaAs; heat transfer in thin silicon films; quantum wells; a picosecond electron source; modeling of III-V semiconductors; nonlinear optics properties of materials; femtosecond spectroscopy of the internal dynamics of proteins; computer simulation of protein dynamics; electron solvation; reactions of radicals in micella phase; sarcoma; and medical applications of pulsed lasers is presented [fr
Robustness of Greenberger-Horne-Zeilinger and W states for teleportation in external environments
Energy Technology Data Exchange (ETDEWEB)
Hu Mingliang, E-mail: mingliang0301@163.co [School of Science, Xi' an University of Posts and Telecommunications, Xi' an 710061 (China)
2011-01-31
By solving analytically a master equation in the Lindblad form, we study quantum teleportation of the one-qubit state under the influence of different surrounding environments, and compared the robustness between Greenberger-Horne-Zeilinger (GHZ) and W states in terms of their teleportation capacity. The results revealed that when subject to zero temperature environment, the GHZ state is always more robust than the W state, while the reverse situation occurs when the channel is subject to infinite temperature or dephasing environment.
Optimal detection of entanglement in Greenberger-Horne-Zeilinger states
International Nuclear Information System (INIS)
Kay, Alastair
2011-01-01
We present a broad class of N-qubit Greenberger-Horne-Zeilinger (GHZ)-diagonal states such that nonpositivity under the partial transpose operation is necessary and sufficient for the presence of entanglement, including many naturally arising instances such as dephased GHZ states. Furthermore, our proof directly leads to an entanglement witness which saturates this bound. The witness is applied to thermal GHZ states to prove that the entanglement can be extremely robust to system imperfections.
Robustness of Greenberger-Horne-Zeilinger and W states for teleportation in external environments
International Nuclear Information System (INIS)
Hu Mingliang
2011-01-01
By solving analytically a master equation in the Lindblad form, we study quantum teleportation of the one-qubit state under the influence of different surrounding environments, and compared the robustness between Greenberger-Horne-Zeilinger (GHZ) and W states in terms of their teleportation capacity. The results revealed that when subject to zero temperature environment, the GHZ state is always more robust than the W state, while the reverse situation occurs when the channel is subject to infinite temperature or dephasing environment.
Electric Dipole Echoes in Rydberg Atoms
International Nuclear Information System (INIS)
Yoshida, S.; Reinhold, C. O.; Burgdoerfer, J.; Zhao, W.; Mestayer, J. J.; Lancaster, J. C.; Dunning, F. B.
2007-01-01
We report the first observation of echoes in the electric dipole moment of an ensemble of Rydberg atoms precessing in an external electric field F. Rapid reversal of the field direction is shown to play a role similar to that of a π pulse in NMR in rephasing a dephased ensemble of electric dipoles resulting in the buildup of an echo. The mechanisms responsible for this are discussed with the aid of classical trajectory Monte Carlo simulations
Young Investigator Program: Modular Paradigm for Scalable Quantum Information
2016-03-04
actuator When both direct driving and a quantum controller are available, one can take advantage of both to achieve faster driving of the qubit. In...pointing to advantages to be found in particular geometries for larger quantum information architectures. • We investigated the effect of dephasing and...Montangero, T. Calarco, F. Nori, and M. B. Plenio, “Scal- able quantum computation via local control of only two qubits,” Phys. Rev. A, vol. 81, no. 4, p
Rotational-echo Double-resonance in Complex Biopolymers: a Study of Nephila Clavipes Dragline Silk
International Nuclear Information System (INIS)
Michal, Carl A.; Jelinski, Lynn W.
1998-01-01
Rotational-Echo Double-Resonance (REDOR) NMR on strategically 13C and 15N labeled samples is used to study the conformation of the LGXQ (X = S, G, or N) motif in the major ampullate gland dragline silk from the spider Nephila clavipes. A method is described for calculating REDOR dephasing curves suitable for background subtractions, using probability distributions of nitrogen atoms surrounding a given carbon site, which are developed from coordinates in the Brookhaven Protein Data Bank. The validity of the method is established by comparison to dephasings observed from natural abundance 13C peaks for G and A. Straightforward fitting of universal REDOR dephasing curves to the background corrected peaks of interest provide results which are not self-consistent, and a more sophisticated analysis is developed which better accounts for 15N labels which have scrambled from the intended positions. While there is likely some heterogeneity in the structures formed by the LGXQ sequences, the data indicate that they all form compact turn-like structures
Coherent chemical kinetics as quantum walks. II. Radical-pair reactions in Arabidopsis thaliana
Chia, A.; Górecka, A.; Kurzyński, P.; Paterek, T.; Kaszlikowski, D.
2016-03-01
We apply the quantum-walk approach proposed in the preceding paper [A. Chia et al., preceding paper, Phys. Rev. E 93, 032407 (2016), 10.1103/PhysRevE.93.032407] to a radical-pair reaction where realistic estimates for the intermediate transition rates are available. The well-known average hitting time from quantum walks can be adopted as a measure of how quickly the reaction occurs and we calculate this for varying degrees of dephasing in the radical pair. The time for the radical pair to react to a product is found to be independent of the amount of dephasing introduced, even in the limit of no dephasing where the transient population dynamics exhibits strong coherent oscillations. This can be seen to arise from the existence of a rate-limiting step in the reaction and we argue that in such examples, a purely classical model based on rate equations can be used for estimating the time scale of the reaction but not necessarily its population dynamics.
Mapping protein–protein interactions by double-REDOR-filtered magic angle spinning NMR spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Guo, Changmiao; Hou, Guangjin, E-mail: hou@udel.edu; Lu, Xingyu; Polenova, Tatyana, E-mail: tpolenov@udel.edu [University of Delaware, Department of Chemistry and Biochemistry (United States)
2017-02-15
REDOR-based experiments with simultaneous {sup 1}H–{sup 13}C and {sup 1}H−{sup 15}N dipolar dephasing are explored for investigating intermolecular protein–protein interfaces in complexes formed by a U–{sup 13}C,{sup 15}N-labeled protein and its natural abundance binding partner. The application of a double-REDOR filter (dREDOR) results in a complete dephasing of proton magnetization in the U–{sup 13}C,{sup 15}N-enriched molecule while the proton magnetization of the unlabeled binding partner is not dephased. This retained proton magnetization is then transferred across the intermolecular interface by {sup 1}H–{sup 13}C or {sup 1}H–{sup 15}N cross polarization, permitting to establish the residues of the U–{sup 13}C,{sup 15}N-labeled protein, which constitute the binding interface. To assign the interface residues, this dREDOR-CPMAS element is incorporated as a building block into {sup 13}C–{sup 13}C correlation experiments. We established the validity of this approach on U–{sup 13}C,{sup 15}N-histidine and on a structurally characterized complex of dynactin’s U–{sup 13}C,{sup 15}N-CAP-Gly domain with end-binding protein 1 (EB1). The approach introduced here is broadly applicable to the analysis of intermolecular interfaces when one of the binding partners in a complex cannot be isotopically labeled.
Recombination yield of geminate radical pairs in low magnetic fields - A Green's function method
International Nuclear Information System (INIS)
Doktorov, A.B.; Hansen, M.J.; Pedersen, J. Boiden
2006-01-01
An analytic expression for the recombination yield of a geminate radical pair with a single spin one half nuclei is derived. The expression is valid for any field strength of the static magnetic field. It is assumed that the spin mixing is caused solely by the hyperfine interaction of the nuclear spin and the difference in Zeeman energies of the two radical partners, that the recombination occurs at the distance of closest approach, and that there is a locally strong dephasing at contact. This is a special result of a new general approach where a Green's function technique is used to recast the stochastic Liouville equation into a low dimensional matrix equation that is particularly convenient for locally strong dephasing systems. The equation is expressed in terms of special values (determined by the magnetic parameters) of the Green's function for the relative motion of the radicals and it is therefore valid for any motional model, e.g. diffusion, one and two site models. The applicability of the strong dephasing approximation is illustrated by comparison with numerical exact results
Effects of electron-electron interactions on electronic transport in disordered systems
International Nuclear Information System (INIS)
Foley, Simon Timothy
2002-01-01
This thesis is concerned with the role of electron-electron interactions on electronic transport in disordered systems. We first consider a novel non-linear sigma model in order to microscopically treat the effects of disorder and electronic interaction. We successfully reproduce the perturbative results for the zero-bias anomaly and the interaction correction to the conductivity in a weakly disordered system, and discuss possible directions for future work. Secondly we consider the fluctuations of the dephasing rate for a closed diffusive and quantum dot system. Using the Keldysh technique we derive an expression for the inelastic scattering rate with which we self-consistently obtain the fluctuations in the dephasing rate. For the diffusive regime we find the relative fluctuations is given by F ∼ (L φ /L) 2 /g 2 , where g is the dimensionless conductance, L φ is the dephasing length and L is the sample size. For the quantum dot regime we find a perturbative divergence due to the presence of the zero mode. By mapping divergent diagrams to those for the two-level correlation function, we conjecture the existence of an exact relation between the two. Finally we discuss the consequences of this relation. (author)
Dynamics of many-body localization in the presence of particle loss
van Nieuwenburg, EPL; Yago Malo, J.; Daley, AJ; Fischer, MH
2018-01-01
At long times, residual couplings to the environment become relevant even in the most isolated experiments, a crucial difficulty for the study of fundamental aspects of many-body dynamics. A particular example is many-body localization in a cold-atom setting, where incoherent photon scattering introduces both dephasing and particle loss. Whereas dephasing has been studied in detail and is known to destroy localization already on the level of non-interacting particles, the effect of particle loss is less well understood. A difficulty arises due to the ‘non-local’ nature of the loss process, complicating standard numerical tools using matrix product decomposition. Utilizing symmetries of the Lindbladian dynamics, we investigate the particle loss on both the dynamics of observables, as well as the structure of the density matrix and the individual states. We find that particle loss in the presence of interactions leads to dissipation and a strong suppression of the (operator space) entanglement entropy. Our approach allows for the study of the interplay of dephasing and loss for pure and mixed initial states to long times, which is important for future experiments using controlled coupling of the environment.
Roche, Julien; Ying, Jinfa; Shen, Yang; Torchia, Dennis A.; Bax, Ad
2016-07-01
A new and convenient method, named ARTSY-J, is introduced that permits extraction of the 3JHNHα couplings in proteins from the relative intensities in a pair of 15N-1H TROSY-HSQC spectra. The pulse scheme includes 3JHNHα dephasing of the narrower TROSY 1HN-{15N} doublet component during a delay, integrated into the regular two-dimensional TROSY-HSQC pulse scheme, and compares the obtained intensity with a reference spectrum where 3JHNHα dephasing is suppressed. The effect of passive 1Hα spin flips downscales the apparent 3JHNHα coupling by a uniform factor that depends approximately linearly on both the duration of the 3JHNHα dephasing delay and the 1H-1H cross relaxation rate. Using such a correction factor, which accounts for the effects of both inhomogeneity of the radiofrequency field and 1Hα spin flips, agreement between prior and newly measured values for the small model protein GB3 is better than 0.3 Hz. Measurement for the HIV-1 protease homodimer (22 kDa) yields 3JHNHα values that agree to better than 0.7 Hz with predictions made on the basis of a previously parameterized Karplus equation. Although for Gly residues the two individual 3JHNHα couplings cannot be extracted from a single set of ARTSY-J spectra, the measurement provides valuable ϕ angle information.
Novelli, Anna; Belzig, Wolfgang; Nitzan, Abraham
2015-01-01
The time evolution and the asymptotic outcome of a Landau-Zener-Stueckelberg-Majorana (LZ) process under continuous weak non-selective measurement is analyzed. We compare two measurement protocols in which the populations of either the adiabatic or the non-adiabatic levels are (continuously and weakly) monitored. The weak measurement formalism, described using a Gaussian Kraus operator, leads to a time evolution characterized by a Markovian dephasing process, which, in the non-adiabatic measurement protocol is similar to earlier studies of LZ dynamics in a dephasing environment. Casting the problem in the language of measurement theory makes it possible for us to compare diabatic and adiabatic measurement scenarios, to consider engineered dephasing as a control device and to examine the manifestation of the Zeno effect under the different measurement protocols. In particular, under measurement of the non-adiabatic populations, the Zeno effect is manifested not as a freezing of the measured system in its initial state, but rather as an approach to equal asymptotic populations of the two diabatic states. This behavior can be traced to the way by which the weak measurement formalism behaves in the strong measurement limit, with a built-in relationship between measurement time and strength.
International Nuclear Information System (INIS)
Novelli, Anna; Belzig, Wolfgang; Nitzan, Abraham
2015-01-01
The time evolution and the asymptotic outcome of a Landau–Zener–Stueckelberg–Majorana (LZ) process under continuous weak non-selective measurement is analyzed. We compare two measurement protocols in which the populations of either the adiabatic or the non-adiabatic levels are (continuously and weakly) monitored. The weak measurement formalism, described using a Gaussian Kraus operator, leads to a time evolution characterized by a Markovian dephasing process, which, in the non-adiabatic measurement protocol is similar to earlier studies of LZ dynamics in a dephasing environment. Casting the problem in the language of measurement theory makes it possible for us to compare diabatic and adiabatic measurement scenarios, to consider engineered dephasing as a control device and to examine the manifestation of the Zeno effect under the different measurement protocols. In particular, under measurement of the non-adiabatic populations, the Zeno effect is manifested not as a freezing of the measured system in its initial state, but rather as an approach to equal asymptotic populations of the two diabatic states. This behavior can be traced to the way by which the weak measurement formalism behaves in the strong measurement limit, with a built-in relationship between measurement time and strength. (paper)
Femtosecond time-resolved vibrational SFG spectroscopy of CO/Ru( 0 0 1 )
Hess, Ch.; Wolf, M.; Roke, S.; Bonn, M.
2002-04-01
Vibrational sum-frequency generation (SFG) employing femtosecond infrared (IR) laser pulses is used to study the dynamics of the C-O stretch vibration on Ru(0 0 1). Time-resolved measurements of the free induction decay (FID) of the IR-polarization for 0.33 ML CO/Ru(0 0 1) exhibit single exponential decays over three decades corresponding to dephasing times of T2=1.94 ps at 95 K and T2=1.16 ps at 340 K. This is consistent with pure homogeneous broadening due to anharmonic coupling with the thermally activated low-frequency dephasing mode together with a contribution from saturation of the IR transition. In pump-probe SFG experiments using a strong visible (VIS) pump pulse the perturbation of the FID leads to transient line shifts even at negative delay times, i.e. when the IR-VIS SFG probe pair precedes the pump pulse. Based on an analysis of the time-dependent polarization we discuss the influence of the perturbed FID on time-resolved SFG spectra. We investigate how coherent effects affect the SFG spectra and we examine the time resolution in these experiments, in particular in dependence of the dephasing time.
Luthra, Suman A; Utz, Marcel; Gorman, Eric M; Pikal, Michael J; Munson, Eric J; Lubach, Joseph W
2012-01-01
In this study, changes in the local conformation of aspartame were observed in annealed lyophilized glasses by monitoring changes in the distance between two labeled sites using C-(2)H rotational-echo double-resonance (REDOR) nuclear magnetic resonance (NMR) spectroscopy. Confirmation that the REDOR experiments were producing accurate distance measurement was ensured by measuring the (13)C-(15)N distance in glycine. The experiment was further verified by measuring the REDOR dephasing curve on (13)C-(2)H methionine. (13)C-(2)H REDOR dephasing curves were then measured on lyophilized aspartame-disaccharide formulations. In aspartame-sucrose formulation, the internuclear distances increased upon annealing, which correlated with decreased chemical reactivity. By contrast, annealing had only a minimal effect on the dephasing curve in aspartame-trehalose formulation. The results show that stability is a function of both mobility and local structure (conformation), even in a small molecule system such as lyophilized aspartame-sucrose. Copyright © 2011 Wiley-Liss, Inc.
Exciton coherence in semiconductor quantum dots
International Nuclear Information System (INIS)
Ishi-Hayase, Junko; Akahane, Kouichi; Yamamoto, Naokatsu; Sasaki, Masahide; Kujiraoka, Mamiko; Ema, Kazuhiro
2009-01-01
The coherent dynamics of excitons in InAs quantum dots (QDs) was investigated in the telecommunication wavelength range using a transient four-wave mixing technique. The sample was fabricated on an InP(311)B substrate using strain compensation to control the emission wavelength. This technique also enabled us to fabricate a 150-layer stacked QD structure for obtaining a high S/N in the four-wave mixing measurements, although no high-sensitive heterodyne detection was carried out. The dephasing time and transition dipole moment were precisely estimated from the polarization dependence of signals, taking into account their anisotropic properties. The population lifetimes of the excitons were also measured by using a polarization-dependent pumpprobe technique. A quantitative comparison of these anisotropies demonstrates that in our QDs, non-radiative population relaxation, polarization relaxation and pure dephasing are considerably smaller than the radiative relaxation. A comparison of the results of the four-wave mixing and pump-probe measurements revealed that the pure dephasing could be directly estimated with an accuracy of greater than 0.1 meV by comparing the results of four-wave mixing and pump-probe measurements. (copyright 2009 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)
Vanicek, Jiri
2014-03-01
Rigorous quantum-mechanical calculations of coherent ultrafast electronic spectra remain difficult. I will present several approaches developed in our group that increase the efficiency and accuracy of such calculations: First, we justified the feasibility of evaluating time-resolved spectra of large systems by proving that the number of trajectories needed for convergence of the semiclassical dephasing representation/phase averaging is independent of dimensionality. Recently, we further accelerated this approximation with a cellular scheme employing inverse Weierstrass transform and optimal scaling of the cell size. The accuracy of potential energy surfaces was increased by combining the dephasing representation with accurate on-the-fly ab initio electronic structure calculations, including nonadiabatic and spin-orbit couplings. Finally, the inherent semiclassical approximation was removed in the exact quantum Gaussian dephasing representation, in which semiclassical trajectories are replaced by communicating frozen Gaussian basis functions evolving classically with an average Hamiltonian. Among other examples I will present an on-the-fly ab initio semiclassical dynamics calculation of the dispersed time-resolved stimulated emission spectrum of the 54-dimensional azulene. This research was supported by EPFL and by the Swiss National Science Foundation NCCR MUST (Molecular Ultrafast Science and Technology) and Grant No. 200021124936/1.
Johnson, Robert L.; Anderson, Jason M.; Shanks, Brent H.; Fang, Xiaowen; Hong, Mei; Schmidt-Rohr, Klaus
2013-09-01
Two robust combinations of spectral editing techniques with 2D 13Csbnd 13C NMR have been developed for characterizing the aromatic components of 13C-enriched low-temperature carbon materials. One method (exchange with protonated and nonprotonated spectral editing, EXPANSE) selects cross peaks of protonated and nearby nonprotonated carbons, while the other technique, dipolar-dephased double-quantum/single-quantum (DQ/SQ) NMR, selects signals of bonded nonprotonated carbons. Both spectra are free of a diagonal ridge, which has many advantages: Cross peaks on the diagonal or of small intensity can be detected, and residual spinning sidebands or truncation artifacts associated with the diagonal ridge are avoided. In the DQ/SQ experiment, dipolar dephasing of the double-quantum coherence removes protonated-carbon signals; this approach also eliminates the need for high-power proton decoupling. The initial magnetization is generated with minimal fluctuation by combining direct polarization, cross polarization, and equilibration by 13C spin diffusion. The dipolar dephased DQ/SQ spectrum shows signals from all linkages between aromatic rings, including a distinctive peak from polycondensed aromatics. In EXPANSE NMR, signals of protonated carbons are selected in the first spectral dimension by short cross polarization combined with dipolar dephasing difference. This removes ambiguities of peak assignment to overlapping signals of nonprotonated and protonated aromatic carbons, e.g. near 125 ppm. Spin diffusion is enhanced by dipolar-assisted rotational resonance. Before detection, Csbnd H dipolar dephasing by gated decoupling is applied, which selects signals of nonprotonated carbons. Thus, only cross peaks due to magnetization originating from protonated C and ending on nearby nonprotonated C are retained. Combined with the chemical shifts deduced from the cross-peak position, this double spectral editing defines the bonding environment of aromatic, COO, and Cdbnd O carbons
Quantum computation: algorithms and implementation in quantum dot devices
Gamble, John King
In this thesis, we explore several aspects of both the software and hardware of quantum computation. First, we examine the computational power of multi-particle quantum random walks in terms of distinguishing mathematical graphs. We study both interacting and non-interacting multi-particle walks on strongly regular graphs, proving some limitations on distinguishing powers and presenting extensive numerical evidence indicative of interactions providing more distinguishing power. We then study the recently proposed adiabatic quantum algorithm for Google PageRank, and show that it exhibits power-law scaling for realistic WWW-like graphs. Turning to hardware, we next analyze the thermal physics of two nearby 2D electron gas (2DEG), and show that an analogue of the Coulomb drag effect exists for heat transfer. In some distance and temperature, this heat transfer is more significant than phonon dissipation channels. After that, we study the dephasing of two-electron states in a single silicon quantum dot. Specifically, we consider dephasing due to the electron-phonon coupling and charge noise, separately treating orbital and valley excitations. In an ideal system, dephasing due to charge noise is strongly suppressed due to a vanishing dipole moment. However, introduction of disorder or anharmonicity leads to large effective dipole moments, and hence possibly strong dephasing. Building on this work, we next consider more realistic systems, including structural disorder systems. We present experiment and theory, which demonstrate energy levels that vary with quantum dot translation, implying a structurally disordered system. Finally, we turn to the issues of valley mixing and valley-orbit hybridization, which occurs due to atomic-scale disorder at quantum well interfaces. We develop a new theoretical approach to study these effects, which we name the disorder-expansion technique. We demonstrate that this method successfully reproduces atomistic tight-binding techniques
Possibility of superradiance by magnetic nanoclusters
International Nuclear Information System (INIS)
Yukalov, V I; Yukalova, E P
2011-01-01
The possibility of realizing spin superradiance by an assembly of magnetic nanoclusters is analyzed. The known obstacles for realizing such a coherent radiation by magnetic nanoclusters are their large magnetic anisotropy, strong dephasing dipole interactions, and an essential nonuniformity of their sizes. In order to give a persuasive conclusion, a microscopic theory is developed, providing an accurate description of nanocluster spin dynamics. It is shown that, despite the obstacles, it is feasible to organize such a setup that magnetic nanoclusters would produce strong superradiant emission
One-Step Generation of Multi-Qubit GHZ and W States in Superconducting Transmon Qubit System
International Nuclear Information System (INIS)
Gao Guilong; Huang Shousheng; Wang Mingfeng; Jiang Nianquan; Cai Genchang
2012-01-01
We propose a one-step method to prepare multi-qubit GHZ and W states with transmon qubits capacitively coupled to a superconducting transmission line resonator (TLR). Compared with the scheme firstly introduced by Wang et al. [Phys. Rev. B 81 (2010) 104524], our schemes have longer dephasing time and much shorter operation time because the transmon qubits we used are not only more robust to the decoherence and the unavoidable parameter variations, but also have much stronger coupling constant with TLR. Based on the favourable properties of transmons and TLR, our method is more feasible in experiment. (general)
Stimulated Raman adiabatic passage from an atomic to a molecular Bose-Einstein condensate
International Nuclear Information System (INIS)
Drummond, P.D.; Kheruntsyan, K.V.; Heinzen, D.J.; Wynar, R.H.
2002-01-01
The process of stimulated Raman adiabatic passage (STIRAP) provides a possible route for the generation of a coherent molecular Bose-Einstein condensate (BEC) from an atomic BEC. We analyze this process in a three-dimensional mean-field theory, including atom-atom interactions and nonresonant intermediate levels. We find that the process is feasible, but at larger Rabi frequencies than anticipated from a crude single-mode lossless analysis, due to two-photon dephasing caused by the atomic interactions. We then identify optimal strategies in STIRAP allowing one to maintain high conversion efficiencies with smaller Rabi frequencies and under experimentally less demanding conditions
Multi-server blind quantum computation over collective-noise channels
Xiao, Min; Liu, Lin; Song, Xiuli
2018-03-01
Blind quantum computation (BQC) enables ordinary clients to securely outsource their computation task to costly quantum servers. Besides two essential properties, namely correctness and blindness, practical BQC protocols also should make clients as classical as possible and tolerate faults from nonideal quantum channel. In this paper, using logical Bell states as quantum resource, we propose multi-server BQC protocols over collective-dephasing noise channel and collective-rotation noise channel, respectively. The proposed protocols permit completely or almost classical client, meet the correctness and blindness requirements of BQC protocol, and are typically practical BQC protocols.
International Nuclear Information System (INIS)
Scha''fer, W.; Lo''venich, R.; Fromer, N. A.; Chemla, D. S.
2001-01-01
Recent theories of highly excited semiconductors are based on two formalisms, referring to complementary experimental conditions, the real-time nonequilibrium Green's function techniques and the coherently controlled truncation of the many-particle problem. We present a novel many-particle theory containing both of these methods as limiting cases. As a first example of its application, we investigate four-particle correlations in a strong magnetic field including dephasing resulting from the growth of incoherent one-particle distribution functions. Our results are the first rigorous solution concerning formation and decay of four-particle correlations in semiconductors. They are in excellent agreement with experimental data
13C solid state NMR investigation of natural resins components
International Nuclear Information System (INIS)
Tavares, Maria I.B.; Bathista, Andre L.B.S.; Silva, Emerson O.; Priante Filho, Nicolau; Nogueira, Jose S.
2001-01-01
The objective of this work is to establish and analytical methodology as a routine using solid state nuclear magnetic resonance (NMR) techniques to investigate the mainly chemical components presented in natural resins in bulk. And also to evaluate the molecular behaviour of these resins. The routine solid state techniques allow us to assign the main compounds presented in the resins. Therefore, applying specialised techniques, like variable contact time, delayed contact time, dephasing time and proton spin lattice relaxation time in the rotating frame (T 1 H ρ), more information about chemical structure and molecular dynamic is available
Ultrafast electric phase control of a single exciton qubit
Widhalm, Alex; Mukherjee, Amlan; Krehs, Sebastian; Sharma, Nandlal; Kölling, Peter; Thiede, Andreas; Reuter, Dirk; Förstner, Jens; Zrenner, Artur
2018-03-01
We report on the coherent phase manipulation of quantum dot excitons by electric means. For our experiments, we use a low capacitance single quantum dot photodiode which is electrically controlled by a custom designed SiGe:C BiCMOS chip. The phase manipulation is performed and quantified in a Ramsey experiment, where ultrafast transient detuning of the exciton energy is performed synchronous to double pulse π/2 ps laser excitation. We are able to demonstrate electrically controlled phase manipulations with magnitudes up to 3π within 100 ps which is below the dephasing time of the quantum dot exciton.
Energy Technology Data Exchange (ETDEWEB)
Ziener, Christian Herbert
2008-07-01
The properties of dephasing and the resulting relaxation of the magnetization are the basic principle on which all magnetic resonance imaging methods are based. The signal obtained from the gyrating spins is essentially determined by the properties of the considered tissue. Especially the susceptibility differences caused by magnetized materials (for example, deoxygenated blood, BOLD-effect) or magnetic nanoparticles are becoming more important for biomedical imaging. In the present work, the influence of such field inhomogeneities on the NMR-signal is analyzed. (orig.)
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.
Walker, Thad Gilbert; Lancor, Brian Robert; Wyllie, Robert
2016-05-03
Measurement of a precessional rate of a gas, such as an alkali gas, in a magnetic field is made by promoting a non-uniform precession of the gas in which substantially no net magnetic field affects the gas during a majority of the precession cycle. This allows sensitive gases that would be subject to spin-exchange collision de-phasing to be effectively used for extremely sensitive measurements in the presence of an environmental magnetic field such as the Earth's magnetic field.
DEFF Research Database (Denmark)
Fatnassi, Chemseddine; Boucenna, Rachid; Zaidi, Habib
2017-01-01
PURPOSE: In 3D gradient echo magnetic resonance imaging (MRI), strong field gradients B0macro are visually observed at air/tissue interfaces. At low spatial resolution in particular, the respective field gradients lead to an apparent increase in intravoxel dephasing, and subsequently, to signal...... loss or inaccurate R2* estimates. If the strong field gradients are measured, their influence can be removed by postprocessing. METHODS: Conventional corrections usually assume a linear phase evolution with time. For high macroscopic gradient inhomogeneities near the edge of the brain...
Control of photon storage time using phase locking.
Ham, Byoung S
2010-01-18
A photon echo storage-time extension protocol is presented by using a phase locking method in a three-level backward propagation scheme, where phase locking serves as a conditional stopper of the rephasing process in conventional two-pulse photon echoes. The backward propagation scheme solves the critical problems of extremely low retrieval efficiency and pi rephasing pulse-caused spontaneous emission noise in photon echo based quantum memories. The physics of the storage time extension lies in the imminent population transfer from the excited state to an auxiliary spin state by a phase locking control pulse. We numerically demonstrate that the storage time is lengthened by spin dephasing time.
DEFF Research Database (Denmark)
Gobron, Olivier; Jung, K.; Galland, N.
2017-01-01
Frequency-locking a laser to a spectral hole in rare-earth doped crystals at cryogenic temperature has been shown to be a promising alternative to the use of high finesse Fabry-Perot cavities when seeking a very high short term stability laser (M. J. Thorpe et al., Nature Photonics 5, 688 (2011......)). We demonstrate here a novel technique for achieving such stabilization, based on generating a heterodyne beat-note between a master laser and a slave laser whose dephasing caused by propagation near a spectral hole generate the error signal of the frequency lock. The master laser is far detuned from...
Energy Technology Data Exchange (ETDEWEB)
Gelin, Maxim F.; Domcke, Wolfgang [Department of Chemistry, Technische Universität München, D-85747 Garching (Germany); Rao, B. Jayachander [Departamento de Química and Centro de Química, Universidade de Coimbra, 3004-535 Coimbra (Portugal)
2016-05-14
We give a detailed theoretical analysis of the simplest variant of femtosecond stimulated Raman spectroscopy, where a picosecond Raman pump pulse and a femtosecond Raman probe pulse are applied resonantly to a chromophore in thermal equilibrium in the ground electronic state. We demonstrate that this technique is capable of the detection of dephasing-free Raman-like lines revealing vibrational modes not only in the electronic ground state but also in the excited electronic state of the chromophore. The analytical results obtained with simplifying assumptions for the shape of the laser pulses are substantiated by numerical simulations with realistic laser pulses, employing the equation-of-motion phase-matching approach.
Physics at the FMQT’08 conference
Špička, V.; Nieuwenhuizen, Th. M.; Keefe, P. D.
2010-01-01
This paper summarizes the recent state of the art of the following topics presented at the FQMT’08 conference: Foundations of quantum physics, Quantum measurement; Quantum noise, decoherence and dephasing; Cold atoms and Bose-Einstein condensation; Physics of quantum computing and information; Nonequilibrium quantum statistical mechanics; Quantum, mesoscopic and partly classical thermodynamics; Mesoscopic, nano-electro-mechanical systems and optomechanical systems; Spins systems and their dynamics, Brownian motion and molecular motors; Physics of biological systems, and Relevant experiments from the nanoscale to the macroscale. To all these subjects an introduction is given and the recent literature is overviewed. The paper contains some 680 references in total.
Optical Two Dimensional Fourier Transform Spectroscopy of Layered Metal Dichalcogenides
Dey, P.; Paul, J.; Stevens, C. E.; Kovalyuk, Z. D.; Kudrynskyi, Z. R.; Romero, A. H.; Cantarero, A.; Hilton, D. J.; Shan, J.; Karaiskaj, D.; Z. D. Kovalyuk; Z. R. Kudrynskyi Collaboration; A. H. Romero Collaboration; A. Cantarero Collaboration; D. J. Hilton Collaboration; J. Shan Collaboration
2015-03-01
Nonlinear two-dimensional Fourier transform (2DFT) measurements were used to study the mechanism of excitonic dephasing and probe the electronic structure of the excitonic ground state in layered metal dichalcogenides. Temperature-dependent 2DFT measurements were performed to probe exciton-phonon interactions. Excitation density dependent 2DFT measurements reveal exciton-exciton and exciton-carrier scattering, and the lower limit for the homogeneous linewidth of excitons on positively and negatively doped samples. U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Award DE-SC0012635.
Photonic Mach-Zehnder modulators driven by surface acoustic waves in AlGaAs technology
Crespo-Poveda, A.; Gargallo, B.; Artundo, I.; Doménech, J. D.; Muñoz, P.; Hey, R.; Biermann, K.; Tahraoui, A.; Santos, P. V.; Cantarero, A.; de Lima, M. M.
2014-03-01
In this paper, photonic devices driven by surface acoustic waves and operating in the GHz frequency range are presented. The devices were designed and fabricated in (Al,Ga)As technology. In contrast to previously realized modulators, where part of the light transmission is lost due to destructive interference, in the present devices light only switches paths, avoiding losses. One of the devices presents two output channels with 180°-dephasing synchronization. Odd multiples of the fundamental driving frequency are enabled by adjusting the applied acoustic power. A second and more complex photonic integrated device, based on the acoustic modulation of tunable Arrayed Waveguide Gratings, is also proposed.
Semiconductor quantum-dot lasers and amplifiers
DEFF Research Database (Denmark)
Hvam, Jørn Märcher; Borri, Paola; Ledentsov, N. N.
2002-01-01
-power surface emitting VCSELs. We investigated the ultrafast dynamics of quantum-dot semiconductor optical amplifiers. The dephasing time at room temperature of the ground-state transition in semiconductor quantum dots is around 250 fs in an unbiased amplifier, decreasing to below 50 fs when the amplifier...... is biased to positive net gain. We have further measured gain recovery times in quantum dot amplifiers that are significantly lower than in bulk and quantum-well semiconductor optical amplifiers. This is promising for future demonstration of quantum dot devices with high modulation bandwidth...
Theory of decoherence in Bose-Einstein condensate interferometry
Energy Technology Data Exchange (ETDEWEB)
Dalton, B J [ARC Centre for Quantum-Atom Optics and Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne, Victoria 3122 (Australia)
2007-05-15
A full treatment of decoherence and dephasing effects in BEC interferometry has been developed based on using quantum correlation functions for treating interferometric effects. The BEC is described via a phase space distribution functional of the Wigner type for the condensate modes and the positive P type for the non-condensate modes. Ito equations for stochastic condensate and non-condensate field functions replace the functional Fokker-Planck equation for the distribution functional and stochastic averages of field function products determine the quantum correlation functions.
International Nuclear Information System (INIS)
Agaisse, R.; Leguen, R.; Ombredane, D.
1960-01-01
The authors present a mechanical device and an electronic control circuit which have been designed to sinusoidally modulate the reactivity of the Proserpine atomic pile. The mechanical device comprises an oscillator and a mechanism assembly. The oscillator is made of cadmium blades which generate the reactivity oscillation. The mechanism assembly comprises a pulse generator for cycle splitting, a gearbox and an engine. The electronic device comprises or performs pulse detection, an on-off device, cycle pulse shaping, phase separation, a dephasing amplifier, electronic switches, counting scales, and control devices. All these elements are briefly presented
International Nuclear Information System (INIS)
Wang Zhangyin; Yuan Hao; Gao Gan; Shi Shouhua
2006-01-01
We present a robust (n,n)-threshold scheme for multiparty quantum secret sharing of key over two collective-noise channels (i.e., the collective dephasing channel and the collective rotating channel) via three-photon mixed states. In our scheme, only if all the sharers collaborate together can they establish a joint key with the message sender and extract the secret message from the sender's encrypted message. This scheme can be implemented using only a Bell singlet, a one-qubit state and polarization identification of single photon, so it is completely feasible according to the present-day technique.
Coherence and relaxation in energy transfer processes in condensed phases
International Nuclear Information System (INIS)
Shelby, R.M.
1978-03-01
Investigations of electronic triplet and vibrational energy transfer dynamics and relaxation processes are presented. Emphasis is placed on understanding the role of coherence and interactions which tend to destroy the coherence. In the case of triplet excitons at low temperatures, the importance of coherence in energy migration can be established, and the average coherence parameters can be experimentally determined. In the case of vibrational excitations, both picosecond spectroscopic studies of vibrational relaxation and spontaneous Raman spectroscopy are used to characterize the dynamics and give increased insight into the nature of the mechanisms responsible for vibrational dephasing. The design and operation of the picosecond apparatus used in these experiments is also described
Coherent response of a semiconductor microcavity in the strong coupling regime
Cassabois, G.; Triques, A. L. C.; Ferreira, R.; Delalande, C.; Roussignol, Ph; Bogani, F.
2000-05-01
We have studied the coherent dynamics of a semiconductor microcavity by means of interferometric correlation measurements with subpicosecond time resolution in a backscattering geometry. Evidence is brought of the resolution of a homogeneous polariton line in an inhomogeneously broadened exciton system. Surprisingly, photon-like polaritons exhibit an inhomogeneous dephasing. Moreover, we observe an unexpected stationary coherence up to 8 ps for the lower polariton branch close to resonance. All these experimental results are well reproduced within the framework of a linear dispersion theory assuming a coherent superposition of the reflectivity and resonant Rayleigh scattering signals with a well-defined relative phase.
Coherent Exciton Dynamics in GaAs-Based Semiconductor Structures
Colocci, M.; Bogani, F.; Ceccherini, S.; Gurioli, M.
We show that a very powerful tool in the investigation of the coherent exciton dynamics in semiconductors is provided by the study of the emitted light after resonant excitation from pairs of phase-locked femtosecond pulses. Under these conditions, not only the full dynamics of the coherent transients (dephasing times, quantum beat periods, etc.) can be obtained from linear experiments, but it can also be obtained a straightforward discrimination between the coherent or incoherent character of the emission by means of spectral filtering.
Exciton-polariton dynamics in a GaAs bulk microcavity
Ceccherini, S.; Gurioli, M.; Bogani, F.; Colocci, M.; Tredicucci, A.; Bassani, F.; Beltram, F.; Sorba, L.
1998-01-01
We present a full analysis of exciton dynamics in a GaAs λ/2 bulk microcavity following excitation by ultrafast laser pulses. Coherent dynamics was probed by means of an interferometric technique; beating and dephasing times were studied for various excitation intensities. At high incident power, population effects begin to show up reducing exciton oscillator strength and suppressing Rabi splitting. This feature produces marked non-linearities in the input-output characteristic of the optical functions, which were studied in view of reaching bistable operation. Theoretical calculations performed within the transfer-matrix framework show good agreement with experimental results.
Narayanaswamy, Arun; Feiner, L F; Meijerink, A; van der Zaag, P J
2009-09-22
Visual color changes between 300 and 510 K were observed in the photoluminescence (PL) of colloidal InP/ZnS core-shell nanocrystals. A subsequent study of PL spectra in the range 2-510 K and fitting the temperature dependent line shift and line width to theoretical models show that the dominant (dephasing) interaction is due to scattering by acoustic phonons of about 23 meV. Low temperature photoluminescence excitation measurements show that the excitonic band gap depends approximately inversely linearly on the quantum dot size d, which is distinctly weaker than the dependence predicted by current theories.
Efficient quantum state transfer in an engineered chain of quantum bits
Sandberg, Martin; Knill, Emanuel; Kapit, Eliot; Vissers, Michael R.; Pappas, David P.
2016-03-01
We present a method of performing quantum state transfer in a chain of superconducting quantum bits. Our protocol is based on engineering the energy levels of the qubits in the chain and tuning them all simultaneously with an external flux bias. The system is designed to allow sequential adiabatic state transfers, resulting in on-demand quantum state transfer from one end of the chain to the other. Numerical simulations of the master equation using realistic parameters for capacitive nearest-neighbor coupling, energy relaxation, and dephasing show that fast, high-fidelity state transfer should be feasible using this method.
International Nuclear Information System (INIS)
Requardt, H.; Deimling, M.; Weber, H.
1986-01-01
Sagittal and axial images obtained using a surface coil suffer from the extreme intensity profile caused by physical properties of the coil and the anatomic entity of subcutaneous fat. The authors present a measuring device that reduces these disadvantages by means of Helmholtz-type coils, and sequences that reduce the fat signal by dephasing its signal part. The extremely short repetition time (<30 msec) allows acquisition times shorter than 10 sec. Breath-holding for this short period to avoid movement artifacts is possible. Images are presented that illustrate the enhanced contrast of spinal tissue and surrounding structures. Comparisons are made with spin-echo and CHESS images
Self-consistent Maxwell-Bloch model of quantum-dot photonic-crystal-cavity lasers
DEFF Research Database (Denmark)
Cartar, William; Mørk, Jesper; Hughes, Stephen
2017-01-01
-level emitters are solved numerically. Phenomenological pure dephasing and incoherent pumping is added to the optical Bloch equations to allow for a dynamical lasing regime, but the cavity-mediated radiative dynamics and gain coupling of each QD dipole (artificial atom) is contained self-consistently within......-mode to multimode lasing is also observed, depending on the spectral peak frequency of the QD ensemble. Using a statistical modal analysis of the average decay rates, we also show how the average radiative decay rate decreases as a function of cavity size. In addition, we investigate the role of structural disorder...
Protected quantum computing: interleaving gate operations with dynamical decoupling sequences.
Zhang, Jingfu; Souza, Alexandre M; Brandao, Frederico Dias; Suter, Dieter
2014-02-07
Implementing precise operations on quantum systems is one of the biggest challenges for building quantum devices in a noisy environment. Dynamical decoupling attenuates the destructive effect of the environmental noise, but so far, it has been used primarily in the context of quantum memories. Here, we experimentally demonstrate a general scheme for combining dynamical decoupling with quantum logical gate operations using the example of an electron-spin qubit of a single nitrogen-vacancy center in diamond. We achieve process fidelities >98% for gate times that are 2 orders of magnitude longer than the unprotected dephasing time T2.
Simulation of noise-assisted transport via optical cavity networks
International Nuclear Information System (INIS)
Caruso, Filippo; Plenio, Martin B.; Spagnolo, Nicolo; Vitelli, Chiara; Sciarrino, Fabio
2011-01-01
Recently, the presence of noise has been found to play a key role in assisting the transport of energy and information in complex quantum networks and even in biomolecular systems. Here we propose an experimentally realizable optical network scheme for the demonstration of the basic mechanisms underlying noise-assisted transport. The proposed system consists of a network of coupled quantum-optical cavities, injected with a single photon, whose transmission efficiency can be measured. Introducing dephasing in the photon path, this system exhibits a characteristic enhancement of the transport efficiency that can be observed with presently available technology.
Observation of electron weak localization and correlation effects in disordered graphene
Institute of Scientific and Technical Information of China (English)
无
2009-01-01
We have studied the electron transport properties of a disordered graphene sample, where the disorder was intentionally strengthened by Ga+ ion irradiation. The magneto-conductance of the sample exhibits a typical two-dimensional electron weak localization behavior, with electron-electron interaction as the dominant dephasing mechanism. The absence of electron anti-weak localization in the sample implies strong intersublattice and/or intervalley scattering caused by the disorders. The temperature and bias-voltage dependencies of conductance clearly reveal the suppression of conductance at low energies, indicating opening of a Coulomb gap due to electron-electron interaction in the disordered graphene sample.
International Nuclear Information System (INIS)
Yang, Chun-Wei; Hwang, Tzonelih; Tsai, Chia-Wei
2014-01-01
This work proposes controlled quantum secure direct communication (CQSDC) over an ideal channel. Based on the proposed CQSDC, two fault-tolerant CQSDC protocols that are robust under two kinds of collective noises, collective-dephasing noise and collective-rotation noise, respectively, are constructed. Due to the use of quantum entanglement of the Bell state (or logical Bell state) as well as dense coding, the proposed protocols provide easier implementation as well as better qubit efficiency than other CQSDC protocols. Furthermore, the proposed protocols are also free from correlation-elicitation attack and other well-known attacks. (paper)
Dynamics of Dangling Od-Stretch at the Air/water Interface by Heterodyne-Detected Sfg Spectroscopy
Stiopkin, I. V.; Weeraman, C.; Shalhout, F.; Benderskii, A. V.
2009-06-01
SFG spectra of dangling OD-stretch at the air/water interface contain information on vibrational dephasing dynamics, ultrafast reorientational molecular motion, and vibrational energy transfer. To better separate these processes we conducted heterodyne-detected SFG experiments to measure real and imaginary contributions of the SFG spectrum of the dangling OD-stretch at the air/D_2O interface for SSP, PPP, and SPS polarizations. Variations in the temporal profiles of the SFG signals for these three polarizations will be also discussed.
Continuous-Wave Single-Photon Transistor Based on a Superconducting Circuit
DEFF Research Database (Denmark)
Kyriienko, Oleksandr; Sørensen, Anders Søndberg
2016-01-01
We propose a microwave frequency single-photon transistor which can operate under continuous wave probing and represents an efficient single microwave photon detector. It can be realized using an impedance matched system of a three level artificial ladder-type atom coupled to two microwave cavities...... and the appearance of a photon flux leaving the second cavity through a separate input-output port. The proposal does not require time variation of the probe signals, thus corresponding to a passive version of a single-photon transistor. The resulting device is robust to qubit dephasing processes, possesses low dark...
Coherent versus incoherent dynamics in InAs quantum-dot active wave guides
DEFF Research Database (Denmark)
Borri, Paola; Langbein, W.; Hvam, Jørn Märcher
2001-01-01
Coherent dynamics measured by time-resolved four-wave mixing is compared to incoherent population dynamics measured by differential transmission spectroscopy on the ground-state transition at room temperature of two types of InAs-based quantum dots with different confinement energies. The measure....... The measurements are performed with heterodyne detection on quantum-dot active wave guides to enhance the light-matter interaction length. An elastic nature of the measured dephasing is revealed which is independent of the dot energy level scheme....
Constraints on relaxation rates for N-level quantum systems
International Nuclear Information System (INIS)
Schirmer, S.G.; Solomon, A.I.
2004-01-01
We study the constraints imposed on the population and phase relaxation rates by the physical requirement of completely positive evolution for open N-level systems. The Lindblad operators that govern the evolution of the system are expressed in terms of observable relaxation rates, explicit formulas for the decoherence rates due to population relaxation are derived, and it is shown that there are additional, nontrivial constraints on the pure dephasing rates for N>2. Explicit, experimentally testable inequality constraints for the decoherence rates are derived for three- and four-level systems, and the implications of the results are discussed for generic ladder, Λ, and V systems and transitions between degenerate energy levels
Reducing quantum control for spin-spin entanglement distribution
International Nuclear Information System (INIS)
Ciccarello, F; Zarcone, M; Paternostro, M; Palma, G M
2009-01-01
We present a protocol that sets maximum stationary entanglement between remote spins through scattering of mobile mediators without initialization, post-selection or feedback of the mediators' state. No time-resolved tuning is needed and, counterintuitively, the protocol generates two-qubit singlet states even when classical mediators are used. The mechanism responsible for this effect is resilient against non-optimal coupling strengths and dephasing affecting the spins. The scheme uses itinerant particles and scattering centres and can be implemented in various settings. When quantum dots and photons are used a striking result is found: injection of classical mediators, rather than quantum ones, improves the scheme efficiency.
Twisting dirac fermions: circular dichroism in bilayer graphene
Suárez Morell, E.; Chico, Leonor; Brey, Luis
2017-09-01
Twisted bilayer graphene is a chiral system which has been recently shown to present circular dichroism. In this work we show that the origin of this optical activity is the rotation of the Dirac fermions’ helicities in the top and bottom layer. Starting from the Kubo formula, we obtain a compact expression for the Hall conductivity that takes into account the dephasing of the electromagnetic field between the top and bottom layers and gathers all the symmetries of the system. Our results are based in both a continuum and a tight-binding model, and they can be generalized to any two-dimensional Dirac material with a chiral stacking between layers.
Theory of the cancellation of 4-photon resonances by an off-resonance 3-photon cancellation
DEFF Research Database (Denmark)
Elk, M.; Lambropoulos, P.; Tang, X.
1992-01-01
We present a complete account of our recent work [Phys. Rev. A 44, 31 (1991)] in which we investigate the theory of cancellation by interference between the absorption of three fundamental laser photons and one third-harmonic photon. The theory is formulated in terms of the density matrix so...... as to take detunings, dephasing, and laser bandwidth into account. The result is a theory of cancellation for finite detuning that explains how four-photon resonances can be canceled by a three-photon mechanism if there is an atomic level at near-three-photon resonance. The treatment is extended to focused...
Susceptibility effects in nuclear magnetic resonance imaging
International Nuclear Information System (INIS)
Ziener, Christian Herbert
2008-01-01
The properties of dephasing and the resulting relaxation of the magnetization are the basic principle on which all magnetic resonance imaging methods are based. The signal obtained from the gyrating spins is essentially determined by the properties of the considered tissue. Especially the susceptibility differences caused by magnetized materials (for example, deoxygenated blood, BOLD-effect) or magnetic nanoparticles are becoming more important for biomedical imaging. In the present work, the influence of such field inhomogeneities on the NMR-signal is analyzed. (orig.)
International Nuclear Information System (INIS)
Marchenko, T; Carniato, S; Journel, L; Guillemin, R; Kawerk, E; Simon, M; Žitnik, M; Kavčič, M; Bučar, K; Bohinc, R; Petric, M; Da Cruz, V Vaz; Gel'mukhanov, F
2015-01-01
We present an experimental and theoretical study of resonant inelastic x-ray scattering (RIXS) in the CS 2 molecule near the S 1s edge. We show that localization of the S 1s core-hole occurs in CS 2 during the RIXS process due to the orientational dephasing of interference between the waves scattering on the two sulfur atoms. Strong evolution of the RIXS profile with the excitation energy far below the first absorption resonance reflects the onset of electron dynamics triggered by a coherent excitation of multiple electronic states. (paper)
Marchenko , T; Carniato , S; Journel , L; Guillemin , R; Kawerk , E; Žitnik , M; Kavčič , M; Bučar , K; Bohinc , R; Petric , M; da Cruz , V Vaz; Gel'mukhanov , F; Simon , Marielle
2015-01-01
International audience; We present an experimental and theoretical study of resonant inelastic x-ray scattering (RIXS) in the CS2 molecule near the S 1s edge. We show that localization of the S 1s core-hole occurs in CS2 during the RIXS process due to the orientational dephasing of interference between the waves scattering on the two sulfur atoms. Strong evolution of the RIXS profile with the excitation energy far below the first absorption resonance reflects the onset of electron dynamics tr...
Quantum discord of Bell cat states under amplitude damping
International Nuclear Information System (INIS)
Daoud, M; Laamara, R Ahl
2012-01-01
The evolution of pairwise quantum correlations of Bell cat states under amplitude damping is examined using the concept of quantum discord which goes beyond entanglement. A closed expression of the quantum discord is explicitly derived. We used the Koashi–Winter relation, a relation which facilitates the optimization process of the conditional entropy. We also discuss the temporal evolution of bipartite quantum correlations under a dephasing channel and compare the behaviors of quantum discord and entanglement whose properties are characterized through the concurrence. (paper)
Fast Ground State Manipulation of Neutral Atoms in Microscopic Optical Traps
International Nuclear Information System (INIS)
Yavuz, D.D.; Kulatunga, P.B.; Urban, E.; Johnson, T.A.; Proite, N.; Henage, T.; Walker, T.G.; Saffman, M.
2006-01-01
We demonstrate Rabi flopping at MHz rates between ground hyperfine states of neutral 87 Rb atoms that are trapped in two micron sized optical traps. Using tightly focused laser beams we demonstrate high fidelity, site specific Rabi rotations with cross talk on neighboring sites separated by 8 μm at the level of 10 -3 . Ramsey spectroscopy is used to measure a dephasing time of 870 μs, which is ≅5000 times longer than the time for a π/2 pulse
Recent developments in bio-inspired sensors fabricated by additive manufacturing technologies
Krijnen, Gijsbertus J.M.; Sanders, Remco G.P.
2017-01-01
In our work on micro-fabricated hair-sensors, inspired by the flow-sensitive sensors found on crickets, we have made great progress. Initially delivering mediocre performance compared to their natural counter parts they have evolved into capable sensors with thresholds roughly a factor of 30 larger
Supporting Development of Energy-Optimised Java Real-Time Systems using TetaSARTS
DEFF Research Database (Denmark)
Luckow, Kasper Søe; Bøgholm, Thomas; Thomsen, Bent
2013-01-01
This paper presents how the tool TetaSARTS can be used to support the development of embedded hard real-time systems written in Java using the emerging Safety Critical Java (SCJ) profile. TetaSARTS facilitates control-flow sensitive schedulability analysis of a set of real-time tasks, and features...
Hybrid Logical Analyses of the Ambient Calculus
DEFF Research Database (Denmark)
Bolander, Thomas; Hansen, René Rydhof
2007-01-01
In this paper, hybrid logic is used to formulate a rational reconstruction of a previously published control flow analysis for the mobile ambients calculus and we further show how a more precise flow-sensitive analysis, that takes the ordering of action sequences into account, can be formulated...
Biomimetic micromechanical adaptive flow-sensor arrays
Krijnen, Gijsbertus J.M.; Floris, J.; Dijkstra, Marcel; Lammerink, Theodorus S.J.; Wiegerink, Remco J.
2007-01-01
We report current developments in biomimetic flow-sensors based on flow sensitive mechano-sensors of crickets. Crickets have one form of acoustic sensing evolved in the form of mechanoreceptive sensory hairs. These filiform hairs are highly perceptive to low-frequency sound with energy sensitivities
Control system for an artificial heart
Gebben, V. D.; Webb, J. A., Jr.
1970-01-01
Inexpensive industrial pneumatic components are combined to produce control system to drive sac-type heart-assistance blood pump with controlled pulsatile pressure that makes pump rate of flow sensitive to venous /atrial/ pressure, while stroke is centered about set operating point and pump is synchronized with natural heart.
Biomimetic flow-sensor arrays based on the filiform hairs on the cerci of crickets
Wiegerink, Remco J.; Floris, J.; Jaganatharaja, R.K.; Izadi, N.; Lammerink, Theodorus S.J.; Krijnen, Gijsbertus J.M.
2007-01-01
In this paper we report on the latest developments in biomimetic flow-sensors based on the flow sensitive mechano-sensors of crickets. Crickets have one form of acoustic sensing evolved in the form of mechanoreceptive sensory hairs. These filiform hairs are highly perceptive to low-frequency sound
Learning from Crickets: Artificial Hair-Sensor Array Developments
Krijnen, Gijsbertus J.M.; Lammerink, Theodorus S.J.; Wiegerink, Remco J.
2010-01-01
We have successfully developed biomimetic flowsensitive hair-sensor arrays taking inspiration from mechanosensory hairs of crickets. Our current generation of sensors achieves sub mm/s threshold air-flow sensitivity for single hairs operating in a bandwidth of a few hundred Hz and is the result of a
Biomimetic flow sensors for environmental awareness
Krijnen, Gijsbertus J.M.; Dagamseh, A.M.K.
Crickets possess hairy organs attached to their abdomen, the so-called cerci. These cerci contain highly flow-sensitive mechanosensors that enable the crickets to monitor the flow-field around them and react to specific stimuli form the environment, e.g. air-movements generated by hunting spiders.
Trade-off capacities of the quantum Hadamard channels
International Nuclear Information System (INIS)
Bradler, Kamil; Hayden, Patrick; Touchette, Dave; Wilde, Mark M.
2010-01-01
Coding theorems in quantum Shannon theory express the ultimate rates at which a sender can transmit information over a noisy quantum channel. More often than not, the known formulas expressing these transmission rates are intractable, requiring an optimization over an infinite number of uses of the channel. Researchers have rarely found quantum channels with a tractable classical or quantum capacity, but when such a finding occurs, it demonstrates a complete understanding of that channel's capabilities for transmitting classical or quantum information. Here we show that the three-dimensional capacity region for entanglement-assisted transmission of classical and quantum information is tractable for the Hadamard class of channels. Examples of Hadamard channels include generalized dephasing channels, cloning channels, and the Unruh channel. The generalized dephasing channels and the cloning channels are natural processes that occur in quantum systems through the loss of quantum coherence or stimulated emission, respectively. The Unruh channel is a noisy process that occurs in relativistic quantum information theory as a result of the Unruh effect and bears a strong relationship to the cloning channels. We give exact formulas for the entanglement-assisted classical and quantum communication capacity regions of these channels. The coding strategy for each of these examples is superior to a naieve time-sharing strategy, and we introduce a measure to determine this improvement.
Two-pulse and stimulated nuclear-quadrupole-resonance echoes in YAlO3:Pr3+
International Nuclear Information System (INIS)
Erickson, L.E.
1991-01-01
The dephasing of trivalent praseodymium dilute in yttrium aluminum oxide (YAlO 3 ) in the ground electronic state 3 H 4 state is evaluated using an optically detected method, to measure two-rf-pulse- and three-rf-pulse-stimulated nuclear quadrupole echoes. The magnitude of the echo is obtained by detecting the weak Raman optical field generated by the interaction of the magnetic moment of the echo and a light beam resonant with the 3 H 4 (0 cm 1 ) to 1 D 2 (16 374 cm -1 ) optical transition. This same light beam is used as an optical pump (37-ms duration) prior the rf-pulse sequence to increase the population difference of the hyperfine energy levels, thereby improving the echo signal. The light is turned off 9 ms before the rf-pulse sequence and remains off until the echo to avoid optical-pumping effects on the measured nuclear-quadrupole-resonance (NQR) echo lifetime. The dephasing time T 2 from two-pulse nuclear-quadrupole-echo measurement is found to be 366±29 μs
Ultrahigh Error Threshold for Surface Codes with Biased Noise
Tuckett, David K.; Bartlett, Stephen D.; Flammia, Steven T.
2018-02-01
We show that a simple modification of the surface code can exhibit an enormous gain in the error correction threshold for a noise model in which Pauli Z errors occur more frequently than X or Y errors. Such biased noise, where dephasing dominates, is ubiquitous in many quantum architectures. In the limit of pure dephasing noise we find a threshold of 43.7(1)% using a tensor network decoder proposed by Bravyi, Suchara, and Vargo. The threshold remains surprisingly large in the regime of realistic noise bias ratios, for example 28.2(2)% at a bias of 10. The performance is, in fact, at or near the hashing bound for all values of the bias. The modified surface code still uses only weight-4 stabilizers on a square lattice, but merely requires measuring products of Y instead of Z around the faces, as this doubles the number of useful syndrome bits associated with the dominant Z errors. Our results demonstrate that large efficiency gains can be found by appropriately tailoring codes and decoders to realistic noise models, even under the locality constraints of topological codes.
International Nuclear Information System (INIS)
Durstberger, K.; Hasegawa, Y.; Klepp, J.; Sulyok, G.; Rauch, H.
2008-01-01
Full text: Fundamental quantum properties like quantum coherence and entanglement are among the most interesting features of quantum mechanics. The physical system of interest is the (massive) neutron subjected to interferometric and polarimetric measurements. Neutrons are proper objects for a study of quantum mechanical behavior: they allow for rather easy experimental control and the neutron spin is the simplest two-level system with easy manipulation by magnetic fields. In combination with interferometric measurements the system has enough intrinsic richness to show interesting quantum features such as entanglement. The coupling of the neutron to an external magnetic field allows for selective manipulations of the spinor quantum states. This can be used, on the one hand, to create entangled states where the entanglement occurs between different degrees of freedom (e.g. spin and path) and, on the other hand, one can introduce dephasing and decoherence by varying magnetic fields. We investigate different kinds of entanglement for the neutron system and mechanisms for decoherence and dephasing. We discuss weak measurements and their realization for neutrons where information about the system can be revealed without disturbing the system too much. Beyond the theoretical work we develop experimental strategies to check the results directly in suitably designed experiments. The experimental work is done at the Institute Laue-Langvine (ILL) in Grenoble, France. (author)
A fault-tolerant addressable spin qubit in a natural silicon quantum dot
Takeda, Kenta; Kamioka, Jun; Otsuka, Tomohiro; Yoneda, Jun; Nakajima, Takashi; Delbecq, Matthieu R.; Amaha, Shinichi; Allison, Giles; Kodera, Tetsuo; Oda, Shunri; Tarucha, Seigo
2016-01-01
Fault-tolerant quantum computing requires high-fidelity qubits. This has been achieved in various solid-state systems, including isotopically purified silicon, but is yet to be accomplished in industry-standard natural (unpurified) silicon, mainly as a result of the dephasing caused by residual nuclear spins. This high fidelity can be achieved by speeding up the qubit operation and/or prolonging the dephasing time, that is, increasing the Rabi oscillation quality factor Q (the Rabi oscillation decay time divided by the π rotation time). In isotopically purified silicon quantum dots, only the second approach has been used, leaving the qubit operation slow. We apply the first approach to demonstrate an addressable fault-tolerant qubit using a natural silicon double quantum dot with a micromagnet that is optimally designed for fast spin control. This optimized design allows access to Rabi frequencies up to 35 MHz, which is two orders of magnitude greater than that achieved in previous studies. We find the optimum Q = 140 in such high-frequency range at a Rabi frequency of 10 MHz. This leads to a qubit fidelity of 99.6% measured via randomized benchmarking, which is the highest reported for natural silicon qubits and comparable to that obtained in isotopically purified silicon quantum dot–based qubits. This result can inspire contributions to quantum computing from industrial communities. PMID:27536725
Piloting procedure for a pile running below critical level
International Nuclear Information System (INIS)
Lacour, J.; Raievski, V.
1957-01-01
The knowledge of the subcritical state of a reactor in the course of starting up makes it possible to avoid passing too quickly through the critical state. The problem arises every time the pile is put into action again following, for example, an appreciable modification in the fuel charge, or an accidental fall of the security rods during a run at high flux or at high temperature. The method described provides a mean of knowing at each moment the anti-reactivity value of the pile by means of a direct-reading instrument mounted on the control board. This result is obtained by superimposing a fixed frequency oscillation on the normal movement of a control rod, and reading on a phase-meter the dephasing of the neutron density. Theory shows, and experiments confirm, that for a given frequency the dephasing depends only on the lifetime of the fast neutrons, the characteristics of the slow neutrons and the anti-reactivity of the pile. The minimum time necessary for an anti-reactivity determination is equal to a modulation period (from 1 to 4 seconds). (authors) [fr
International Nuclear Information System (INIS)
St Pierre, T G; Clark, P R; Chua-anusorn, W; Fleming, A; Pardoe, H; Jeffrey, G P; Olynyk, J K; Pootrakul, P; Jones, S; Moroz, P
2005-01-01
Magnetic nanoparticles and microparticles can be found in biological tissues for a variety of reasons including pathological deposition of biogenic particles, administration of synthetic particles for scientific or clinical reasons, and the inclusion of biogenic magnetic particles for the sensing of the geomagnetic field. In applied magnetic fields, the magnetisation of tissue protons can be manipulated with radiofrequency radiation such that the macroscopic magnetisation of the protons precesses freely in the plane perpendicular to the applied static field. The presence of magnetic particles within tissue enhances the rate of dephasing of proton precession with higher concentrations of particles resulting in higher dephasing rates. Magnetic resonance imaging instruments can be used to measure and image the rate of decay of spin echo recoverable proton transverse magnetisation (R 2 ) within tissues enabling the measurement and imaging of magnetic particle concentrations with the aid of suitable calibration curves. Applications include the non-invasive measurement of liver iron concentrations in iron-overload disorders and measurement and imaging of magnetic particle concentrations used in magnetic hyperthermia therapy. Future applications may include the tracking of magnetically labelled drugs or biomolecules and the measurement of fibrotic liver damage
Detecting the BCS pairing amplitude via a sudden lattice ramp in a honeycomb lattice
Tiesinga, Eite; Nuske, Marlon; Mathey, Ludwig
2016-05-01
We determine the exact time evolution of an initial Bardeen-Cooper-Schrieffer (BCS) state of ultra-cold atoms in a hexagonal optical lattice. The dynamical evolution is triggered by ramping the lattice potential up, such that the interaction strength Uf is much larger than the hopping amplitude Jf. The quench initiates collective oscillations with frequency | Uf | /(2 π) in the momentum occupation numbers and imprints an oscillating phase with the same frequency on the order parameter Δ. The latter is not reproduced by treating the time evolution in mean-field theory. The momentum density-density or noise correlation functions oscillate at frequency | Uf | /(2 π) as well as its second harmonic. For a very deep lattice, with negligible tunneling energy, the oscillations of momentum occupation numbers are undamped. Non-zero tunneling after the quench leads to dephasing of the different momentum modes and a subsequent damping of the oscillations. This occurs even for a finite-temperature initial BCS state, but not for a non-interacting Fermi gas. We therefore propose to use this dephasing to detect a BCS state. Finally, we predict that the noise correlation functions in a honeycomb lattice will develop strong anti-correlations near the Dirac point. We acknowledge funding from the National Science Foundation.
Demonstration of Protection of a Superconducting Qubit from Energy Decay
Lin, Yen-Hsiang; Nguyen, Long B.; Grabon, Nicholas; San Miguel, Jonathan; Pankratova, Natalia; Manucharyan, Vladimir E.
2018-04-01
Long-lived transitions occur naturally in atomic systems due to the abundance of selection rules inhibiting spontaneous emission. By contrast, transitions of superconducting artificial atoms typically have large dipoles, and hence their lifetimes are determined by the dissipative environment of a macroscopic electrical circuit. We designed a multilevel fluxonium artificial atom such that the qubit's transition dipole can be exponentially suppressed by flux tuning, while it continues to dispersively interact with a cavity mode by virtual transitions to the noncomputational states. Remarkably, energy decay time T1 grew by 2 orders of magnitude, proportionally to the inverse square of the transition dipole, and exceeded the benchmark value of T1>2 ms (quality factor Q1>4 ×107) without showing signs of saturation. The dephasing time was limited by the first-order coupling to flux noise to about 4 μ s . Our circuit validated the general principle of hardware-level protection against bit-flip errors and can be upgraded to the 0 -π circuit [P. Brooks, A. Kitaev, and J. Preskill, Phys. Rev. A 87, 052306 (2013), 10.1103/PhysRevA.87.052306], adding protection against dephasing and certain gate errors.
Quantum transport in the FMO photosynthetic light-harvesting complex.
Karafyllidis, Ioannis G
2017-06-01
The very high light-harvesting efficiency of natural photosynthetic systems in conjunction with recent experiments, which showed quantum-coherent energy transfer in photosynthetic complexes, raised questions regarding the presence of non-trivial quantum effects in photosynthesis. Grover quantum search, quantum walks, and entanglement have been investigated as possible effects that lead to this efficiency. Here we explain the near-unit photosynthetic efficiency without invoking non-trivial quantum effects. Instead, we use non-equilibrium Green's functions, a mesoscopic method used to study transport in nano-conductors to compute the transmission function of the Fenna-Matthews-Olson (FMO) complex using an experimentally derived exciton Hamiltonian. The chlorosome antenna and the reaction center play the role of input and output contacts, connected to the FMO complex. We show that there are two channels for which the transmission is almost unity. Our analysis also revealed a dephasing-driven regulation mechanism that maintains the efficiency in the presence of varying dephasing potentials.
Quantum model for a periodically driven selectivity filter in a K+ ion channel
International Nuclear Information System (INIS)
Cifuentes, A A; Semião, F L
2014-01-01
In this work, we present a quantum transport model for the selectivity filter in the KcsA potassium ion channel. This model is fully consistent with the fact that two conduction pathways are involved in the translocation of ions through the filter, and we show that the presence of a second path may actually bring advantages for the filter as a result of quantum interference. To highlight interferences and resonances in the model, we consider the selectivity filter to be driven by a controlled time-dependent external field, which changes the free-energy scenario and consequently the conduction of the ions. In particular, we demonstrate that the two-pathway conduction mechanism is more advantageous for the filter when dephasing in the transient configurations is lower than in the main configurations. As a matter of fact, K + ions in the main configurations are highly coordinated by oxygen atoms of the filter backbone, and this increases noise. Moreover, we also show that for a wide range of dephasing rates and driving frequencies, the two-pathway conduction used by the filter leads to higher ionic currents than the single–path model. (paper)
Slow modes in spin hydrodynamics of 3He-B
International Nuclear Information System (INIS)
Golo, V.L.; Kats, E.I.
1986-01-01
We study nonlinear interaction between sound and spin modes with the view of finding a means for detecting second sound pumped in a sample of 3 He-B. We find that the interaction could be tangible for second sound and spin-textual waves which are long wavelength spatial modulations of the WP mode of magnetic ringing. We show that within a thin layer close to the loudspeaker second sound generates the dephasing delta psi of the spin precession. We suggest that the mode of the w-oscillations could be detected with the technique for the propagating magnetic disturbance. Our numerical estimates indicate that in te temperature and pressure region 1 - T/Tsub(c) approximately equal to 0.01 and p=21.7 bar, and the frequency and power of second sound of order 100 Hz and 10 -3 erg/s, the dephasing of the spin precession may amount to 0.1 rad, and result in a swinging of the precession axis w
Gong, Zhaoyuan; Walls, Jamie D.
2018-02-01
Delayed-acquisition, which is a common technique for improving spectral resolution in Fourier transform based spectroscopies, typically relies upon differences in T2 relaxation rates that are often due to underlying differences in dynamics and/or complexities of the spin systems being studied. After an acquisition delay, the broad signals from fast T2 -relaxing species are more suppressed relative to the sharp signals from slow T2 -relaxing species. In this paper, an alternative source of differential "dephasing" under delayed-acquisition is demonstrated that is based solely upon the mathematical properties of the line shape and is independent of the underlying spin dynamics and/or complexity. Signals associated with frequencies where the line shape either changes sharply and/or is non-differentiable at some finite order dephase at a much slower rate than those signals associated with frequencies where the line shape is smooth. Experiments employing delayed-acquisition to study interfaces in biphasic samples, to measure spatially-dependent longitudinal relaxation, and to highlight sharp features in NMR spectra are presented.
Constructing quantum dynamics from mixed quantum-classical descriptions
International Nuclear Information System (INIS)
Barsegov, V.; Rossky, P.J.
2004-01-01
The influence of quantum bath effects on the dynamics of a quantum two-level system linearly coupled to a harmonic bath is studied when the coupling is both diagonal and off-diagonal. It is shown that the pure dephasing kernel and the non-adiabatic quantum transition rate between Born-Oppenheimer states of the subsystem can be decomposed into a contribution from thermally excited bath modes plus a zero point energy contribution. This quantum rate can be modewise factorized exactly into a product of a mixed quantum subsystem-classical bath transition rate and a quantum correction factor. This factor determines dynamics of quantum bath correlations. Quantum bath corrections to both the transition rate and the pure dephasing kernel are shown to be readily evaluated via a mixed quantum-classical simulation. Hence, quantum dynamics can be recovered from a mixed quantum-classical counterpart by incorporating the missing quantum bath corrections. Within a mixed quantum-classical framework, a simple approach for evaluating quantum bath corrections in calculation of the non-adiabatic transition rate is presented
Temperature dependence of coherence in transmon qubits
Energy Technology Data Exchange (ETDEWEB)
Schloer, Steffen; Braumueller, Jochen; Lukashenko, Oleksandr; Rotzinger, Hannes; Weides, Martin; Ustinov, Alexey V. [Physikalisches Institut, KIT, Karlsruhe (Germany); Sandberg, Martin; Vissers, Michael R.; Pappas, David P. [NIST, Boulder, CO (United States)
2015-07-01
Superconducting qubits are a promising field of research, not only with respect to quantum computing but also as highly sensitive detectors and due to the possibility of using them to study fundamental implications of quantum mechanics. The requirements for qubits that can be used as building blocks in a potential quantum computer are challenging. Modern superconducting qubits like the transmon are strong candidates for achieving these goals. The main challenge here is to increase the coherence of prepared quantum states. Here, we experimentally investigate the influence of temperature variation on relaxation and dephasing of a transmon qubit. Our goal is to understand decoherence mechanisms in material optimized circuits. Aiming at longer coherence, in this case peaking over 50 μs for T{sub 1} and T{sub 2}, our samples are fabricated at NIST using two different materials. Low-loss TiN was used for the shunt capacitance as well as the resonator, combined with shadow evaporated ultra-small Al-AlO{sub x}-Al Josephson junctions. We will present temperature-dependent data on qubit relaxation and dephasing times as well as power spectra. Our data will be compared to previously obtained temperature dependent data for other types of qubits.
Coherence properties of the 0-π qubit
Groszkowski, Peter; Di Paolo, A.; Grimsmo, A. L.; Blais, A.; Schuster, D. I.; Houck, A. A.; Koch, Jens
2018-04-01
Superconducting circuits rank among some of the most interesting architectures for the implementation of quantum information processing devices. The recently proposed 0-π qubit (Brooks et al 2013 Phys. Rev. A 87 52306) promises increased protection from spontaneous relaxation and dephasing. In this paper we present a detailed theoretical study of the coherence properties of the 0-π device, investigate relevant decoherence channels, and show estimates for achievable coherence times in multiple parameter regimes. In our analysis, we include disorder in circuit parameters, which results in the coupling of the qubit to a low-energy, spurious harmonic mode. We analyze the effects of such coupling on decoherence, in particular dephasing due to photon shot noise, and outline how such a noise channel can be mitigated by appropriate parameter choices. In the end we find that the 0-π qubit performs well and may become an attractive candidate for the implementation of the next-generation superconducting devices for uses in quantum computing and information.
International Nuclear Information System (INIS)
Htoon, H.; Shih, C.K.; Takagahara, T.
2003-01-01
We performed extensive studies on quantum decoherence processes of excitons trapped in the various excited states of SAQDs. Energy level structure and dephasing times of excited states were first determined by conducting photoluminescence excitation spectroscopy and wave-packet interferometry on a large number of individual SAQDs. This large statistical basis allows us to extract the correlation between the energy level structure and dephasing times. The major decoherence mechanisms and their active regime were identified from this correlation. A significant suppression of decoherence was also observed in some of the energetically isolated excited states, providing an experimental evidence for the theoretical prediction, known as 'phonon bottleneck effect'. Furthermore, we observed the direct experimental evidence of Rabi oscillation in these excited states with long decoherence times. In addition, a new type of quantum interference (QI) phenomenon was discovered in the wave-packet interferometry experiments performed in the strong excitation regime where the non-linear effects of Rabi oscillation become important. Detailed theoretical investigations attribute this phenomenon to the coherent dynamics resulting from the interplay of Rabi oscillation and QI
Exploring two-dimensional electron gases with two-dimensional Fourier transform spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Paul, J.; Dey, P.; Karaiskaj, D., E-mail: karaiskaj@usf.edu [Department of Physics, University of South Florida, 4202 East Fowler Ave., Tampa, Florida 33620 (United States); Tokumoto, T.; Hilton, D. J. [Department of Physics, University of Alabama at Birmingham, Birmingham, Alabama 35294 (United States); Reno, J. L. [CINT, Sandia National Laboratories, Albuquerque, New Mexico 87185 (United States)
2014-10-07
The dephasing of the Fermi edge singularity excitations in two modulation doped single quantum wells of 12 nm and 18 nm thickness and in-well carrier concentration of ∼4 × 10{sup 11} cm{sup −2} was carefully measured using spectrally resolved four-wave mixing (FWM) and two-dimensional Fourier transform (2DFT) spectroscopy. Although the absorption at the Fermi edge is broad at this doping level, the spectrally resolved FWM shows narrow resonances. Two peaks are observed separated by the heavy hole/light hole energy splitting. Temperature dependent “rephasing” (S{sub 1}) 2DFT spectra show a rapid linear increase of the homogeneous linewidth with temperature. The dephasing rate increases faster with temperature in the narrower 12 nm quantum well, likely due to an increased carrier-phonon scattering rate. The S{sub 1} 2DFT spectra were measured using co-linear, cross-linear, and co-circular polarizations. Distinct 2DFT lineshapes were observed for co-linear and cross-linear polarizations, suggesting the existence of polarization dependent contributions. The “two-quantum coherence” (S{sub 3}) 2DFT spectra for the 12 nm quantum well show a single peak for both co-linear and co-circular polarizations.
Energy Technology Data Exchange (ETDEWEB)
SCHROEDER,W. ANDREAS; NELSON,THOMAS R.; BORISOV,A.B.; LONGWORTH,J.W.; BOYER,K.; RHODES,C.K.
2000-06-07
A theoretical analysis of laser-driven collisional ejection of inner-shell electrons is presented to explain the previously observed anomalous kilovolt L-shell x-ray emission spectra from atomic Xe cluster targets excited by intense sub-picosecond 248nrn ultraviolet radiation. For incident ponderomotively-driven electrons photoionized by strong above threshold ionization, the collisional ejection mechanism is shown to be highly l-state and significantly n-state (i.e. radially) selective for time periods shorter than the collisional dephasing time of the photoionized electronic wavefunction. The resulting preference for the collisional ejection of 2p electrons by an ionized 4p state produces the measured anomalous Xe(L) emission which contains direct evidence for (i) the generation of Xe{sup 27+}(2p{sup 5}3d{sup 10}) and Xe{sup 28+}(2p{sup 5}3d{sup 9}) ions exhibiting inner-shell population inversion and (ii) a coherent correlated electron state collision responsible for the production of double 2p vacancies. For longer time periods, the selectivity of this coherent impact ionization mechanism is rapidly reduced by the combined effects of intrinsic quantum mechanical spreading and dephasing--in agreement with the experimentally observed and extremely strong {minus}{lambda}{sup {minus}6} pump-laser wavelength dependence of the efficiency of inner-shell (2p) vacancy production in Xe clusters excited in underdense plasmas.
Optical properties of supported core-shell and alloy silver/gold nanoparticles
Energy Technology Data Exchange (ETDEWEB)
Hubenthal, Frank; Traeger, Frank [Universitaet Kassel (Germany)
2008-07-01
For many applications like surface enhanced Raman scattering in which the optical field enhancement associated with surface plasmon excitation is exploited, tunability of this collective resonance over a wide range is required. For this purpose we have prepared core-shell and alloy nanoparticles consisting of Ag and Au. The core-shell nanoparticles were made by subsequent deposition of Ag and Au atoms and vice versa on dielectric substrates followed by diffusion and nucleation. One of the most interesting among the numerous results is that the plasmon frequency can be tuned from 2.8 eV (442 nm) to 2.1 eV (590 nm) depending on the Au shell thickness. Subsequent annealing of the core-shell nanoparticles causes a shift of the resonance frequency to 2.6 eV. Theoretical modelling allows us to attribute this observation to the formation of alloy nanoparticles. Finally, we have measured the dephasing time T{sub 2} of the alloy nanoparticles by means of spectral hole burning. T{sub 2} amounts to 8.1{+-}1.6 fs, in good agreement with the dephasing time T{sub 2}=8.9 fs that is included in the dielectric function of the bulk.
Squeezing survival and transfer in single and double electromagnetically induced transparency
International Nuclear Information System (INIS)
Ding, J L; Hou, B P; Wang, S J
2010-01-01
We investigate the propagation and storage of a squeezed vacuum as the probe light in a collection of N four-level tripod configuration atoms under the condition of single or double electromagnetically induced transparency (EIT). The squeezing of the probe light is well preserved in both the single transparency channel and the double transparency one. On the other hand, the effects of the ground state dephasing rates on the propagation and storage of the squeezed vacuum are investigated. It is found that the maximum squeezing at the transparency points is suppressed by the dephasing rates in single or double EIT. Meanwhile, the mapping of the squeezing of the probe light onto the atomic ground coherences or onto the two atomic dark-state polaritons is also studied. In the absence of the Langevin atomic noise, the quasi-ideal squeezing transfer between the squeezed vacuum and the atomic ground coherences or the dark-state polaritons can be realized in such a system. When considering the Langevin atomic noise, the quantum characteristics of the atomic coherences at resonance are submerged by the Langevin noise, while in the scenario of the dark-state polariton, it is found that squeezing transfer onto one polariton is damaged, but the squeezing transfer onto the other polariton survives even in the presence of the Langevin noise.
Unraveling the nature of coherent beatings in chlorosomes
Energy Technology Data Exchange (ETDEWEB)
Dostál, Jakub [Department of Chemical Physics, Lund University, P.O. Box 124, SE-22100 Lund (Sweden); Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague (Czech Republic); Mančal, Tomáš; Pšenčík, Jakub [Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 121 16 Prague (Czech Republic); Vácha, František [Faculty of Science, University of South Bohemia, Branišovská 31, 370 05 České Budějovice (Czech Republic); Zigmantas, Donatas, E-mail: donatas.zigmantas@chemphys.lu.se [Department of Chemical Physics, Lund University, P.O. Box 124, SE-22100 Lund (Sweden)
2014-03-21
Coherent two-dimensional (2D) spectroscopy at 80 K was used to study chlorosomes isolated from green sulfur bacterium Chlorobaculum tepidum. Two distinct processes in the evolution of the 2D spectrum are observed. The first being exciton diffusion, seen in the change of the spectral shape occurring on a 100-fs timescale, and the second being vibrational coherences, realized through coherent beatings with frequencies of 91 and 145 cm{sup −1} that are dephased during the first 1.2 ps. The distribution of the oscillation amplitude in the 2D spectra is independent of the evolution of the 2D spectral shape. This implies that the diffusion energy transfer process does not transfer coherences within the chlorosome. Remarkably, the oscillatory pattern observed in the negative regions of the 2D spectrum (dominated by the excited state absorption) is a mirror image of the oscillations found in the positive part (originating from the stimulated emission and ground state bleach). This observation is surprising since it is expected that coherences in the electronic ground and excited states are generated with the same probability and the latter dephase faster in the presence of fast diffusion. Moreover, the relative amplitude of coherent beatings is rather high compared to non-oscillatory signal despite the reported low values of the Huang-Rhys factors. The origin of these effects is discussed in terms of the vibronic and Herzberg-Teller couplings.
Perturbative theory of higher-order collision-enhanced wave mixing
International Nuclear Information System (INIS)
Trebino, R.; Rahn, L.A.
1989-01-01
This paper reports on collision-enhanced resonances which represent an interesting class of nonlinear- optical processes. They occur because collisional dephasing can rephase quantum-mechanical amplitudes that ordinarily cancel out exactly, thereby allowing otherwise unobservable wave-mixing resonances to be seen. This is an especially interesting phenomenon because these resonances are coherent effects that are induced by an incoherent process (collisional dephasing). First predicted in the late 1970s and eventually observed in 1981, these novel effects have now been seen in a wide variety of four-wave-mixing experiments, ranging from self-focusing to coherent anti-Stokes Raman spectroscopy. Recently, the authors have extended these observations to higher order, where the authors have shown both experimentally and theoretically the higher-order, collision-enhanced effects exist in nonlinear optics, appearing as subharmonics of two-photon resonances. Indeed, the authors have found that collision-enhanced processes are ideal systems for studying higher-order, nonlinear-optical effects because very high orders can be made to contribute with little or no saturation braodening. Experiments on sodium in a flame using six- and eight-wave-mixing geometries have revealed still higher-order effects (at least as high- order as χ (13) )
Double light-cone dynamics establish thermal states in integrable 1D Bose gases
Langen, T.; Schweigler, T.; Demler, E.; Schmiedmayer, J.
2018-02-01
We theoretically investigate the non-equilibrium dynamics in a quenched pair of one-dimensional Bose gases with density imbalance. We describe the system using its low-energy effective theory, the Luttinger liquid model. In this framework the system shows strictly integrable relaxation dynamics via dephasing of its approximate many-body eigenstates. In the balanced case, this leads to the well-known light-cone-like establishment of a prethermalized state, which can be described by a generalized Gibbs ensemble. In the imbalanced case the integrable dephasing leads to a state that, counter-intuitively, closely resembles a thermal equilibrium state. The approach to this state is characterized by two separate light-cone dynamics with distinct characteristic velocities. This behavior is a result of the fact that in the imbalanced case observables are not aligned with the conserved quantities of the integrable system. We discuss a concrete experimental realization to study this effect using matterwave interferometry and many-body revivals on an atom chip.
International Nuclear Information System (INIS)
Schwinkendorf, Jan-Patrick
2012-05-01
Plasma wakefields are a promising approach for the acceleration of electrons with ultrahigh (10 to 100 GV/m) electric fields. Nowadays, high-intensity laser pulses are routinely utilized to excite these large-amplitude plasma waves. However, several detrimental effects such as laser diffraction, electron-wake dephasing and laser depletion may terminate the acceleration process. Two of these phenomena can be mitigated or avoided by the application of capillary waveguides, e.g. fabricated out of sapphire for longevity. Capillaries may compensate for laser diffraction like a fiber and allow for the creation of tapered gas-density profiles working against the dephasing between the accelerating wave and the particles. Additionally, they offer the possibility of controlled particle injection. This thesis is reporting on the set up of a laser for fs-micromachining of capillaries of almost arbitrary shapes and a test stand for density-profile characterization. These devices will permit the creation of tailored gas-density profiles for controlled electron injection and acceleration inside plasma.
Transport efficiency in open quantum systems with static and dynamical disorder
Zhang, Yang; Celardo, G. Luca; Borgonovi, Fausto; Kaplan, Lev
2017-12-01
We study, under very general conditions and in a variety of geometries, quantum enhancement of transport in open systems. Both static disorder and dephasing associated with dynamical disorder (or finite temperature) are fully included in the analysis. We show that quantum coherence effects may significantly enhance transport in open quantum systems even in the semiclassical regime (where the decoherence rate is greater than the inter-site hopping amplitude), as long as the static disorder is sufficiently strong. When the strengths of static and dynamical disorder are fixed, there is an optimal opening strength at which the coherent transport enhancement is optimized. Analytic results are obtained in two simple paradigmatic tight-binding models of large systems: the linear chain and the fully connected network. The physical behavior is also reflected, for example, in the FMO photosynthetic complex, which may be viewed as being intermediate between these paradigmatic models. We furthermore show that a nonzero dephasing rate assists transport in an open linear chain when the disorder strength exceeds a critical value, and obtain this critical disorder strength as a function of the degree of opening.
Comparison of methods for separating vibration sources in rotating machinery
Klein, Renata
2017-12-01
Vibro-acoustic signatures are widely used for diagnostics of rotating machinery. Vibration based automatic diagnostics systems need to achieve a good separation between signals generated by different sources. The separation task may be challenging, since the effects of the different vibration sources often overlap. In particular, there is a need to separate between signals related to the natural frequencies of the structure and signals resulting from the rotating components (signal whitening), as well as a need to separate between signals generated by asynchronous components like bearings and signals generated by cyclo-stationary components like gears. Several methods were proposed to achieve the above separation tasks. The present study compares between some of these methods. The paper also presents a new method for whitening, Adaptive Clutter Separation, as well as a new efficient algorithm for dephase, which separates between asynchronous and cyclo-stationary signals. For whitening the study compares between liftering of the high quefrencies and adaptive clutter separation. For separating between the asynchronous and the cyclo-stationary signals the study compares between liftering in the quefrency domain and dephase. The methods are compared using both simulated signals and real data.
International Nuclear Information System (INIS)
Marri, E.; Morresi, A.; Paliani, G.; Cataliotti, R.S.; Giorgini, M.G.
1999-01-01
The vibrational dephasing of the ν 1 (C-H, C-D stretching) and ν 3 (C-H, C-D bending) symmetric motions of liquid acetonitrile in its light and fully deuterated forms has been studied in the frame of the vibrational time correlation functions obtained as Fourier transforms of the isotropic Raman spectral distributions and interpreted within the Kubo theory. In addition, the experimental isotropic profiles have been analysed within the bandshape approach formulated by analytical Fourier transformation of the Kubo vibrational time correlation functions in order to derive the relaxation parameters in the frequency domain. The effects of the isotopic (CH 3 CN/CD 3 CN and vice versa) and chemical (CCl 4 ) dilution on the bandshapes and on the vibrational relaxation parameters have been studied. It was observed that the decay rate of ν 1 mode is insensitive to the isotopic dilution but varies appreciably with chemical (CCl 4 ) dilution. The vibrational dephasing of ν 3 mode is qualitatively, but not quantitatively, affected in the same way by chemical dilution and shows a slower modulation regime than that exhibited by the stretching mode. Unlikely from the latter, the ν 3 mode results are slightly affected by the isotopic dilution. Phase relaxation mechanisms of these two motions of acetonitrile in the liquid state are proposed on the basis of these data, and a comparison is made with the results earlier published. (Copyright (c) 1999 Elsevier Science B.V., Amsterdam. All rights reserved.)
Thermalization dynamics of two correlated bosonic quantum wires after a split
Huber, Sebastian; Buchhold, Michael; Schmiedmayer, Jörg; Diehl, Sebastian
2018-04-01
Cherently splitting a one-dimensional Bose gas provides an attractive, experimentally established platform to investigate many-body quantum dynamics. At short enough times, the dynamics is dominated by the dephasing of single quasiparticles, and well described by the relaxation towards a generalized Gibbs ensemble corresponding to the free Luttinger theory. At later times on the other hand, the approach to a thermal Gibbs ensemble is expected for a generic, interacting quantum system. Here, we go one step beyond the quadratic Luttinger theory and include the leading phonon-phonon interactions. By applying kinetic theory and nonequilibrium Dyson-Schwinger equations, we analyze the full relaxation dynamics beyond dephasing and determine the asymptotic thermalization process in the two-wire system for a symmetric splitting protocol. The major observables are the different phonon occupation functions and the experimentally accessible coherence factor, as well as the phase correlations between the two wires. We demonstrate that, depending on the splitting protocol, the presence of phonon collisions can have significant influence on the asymptotic evolution of these observables, which makes the corresponding thermalization dynamics experimentally accessible.
El Sayed, K.; Birkedal, D.; Lyssenko, V. G.; Hvam, J. M.
1997-01-01
We present a theoretical investigation of ultrafast transient four-wave mixing (FWM) of GaAs quantum wells for coherent excitation of excitons and a large number of continuum states. It is shown that in this case the line shape of the FWM signal is drastically altered due to an interaction-induced coupling of the exciton to all the excited continuum states. The signal is dominantly emitted at the spectral position of the exciton and decays, as a function of delay, on a time scale set by the duration of the laser pulse rather than by the intrinsic dephasing time. Nevertheless, the spectral width of the exciton line in the FWM spectrum and in the decay of the time-resolved FWM signal in real time are governed by the intrinsic excitonic dephasing rate. It is shown that for pulse durations of ~ 100 fs (for GaAs quantum wells) this behavior can be explained as the influence of the Coulomb exchange interaction, while for even shorter pulses this behavior is dominantly caused by nonlinear polarization decay.
Time-resolved photon echoes from donor-bound excitons in ZnO epitaxial layers
Poltavtsev, S. V.; Kosarev, A. N.; Akimov, I. A.; Yakovlev, D. R.; Sadofev, S.; Puls, J.; Hoffmann, S. P.; Albert, M.; Meier, C.; Meier, T.; Bayer, M.
2017-07-01
The coherent optical response from 140 nm and 65 nm thick ZnO epitaxial layers is studied using four-wave-mixing spectroscopy with picosecond temporal resolution. Resonant excitation of neutral donor-bound excitons results in two-pulse and three-pulse photon echoes. For the donor-bound A exciton (D0XA ) at temperature of 1.8 K we evaluate optical coherence times T2=33 -50 ps corresponding to homogeneous line widths of 13 -19 μ eV , about two orders of magnitude smaller as compared with the inhomogeneous broadening of the optical transitions. The coherent dynamics is determined mainly by the population decay with time T1=30 -40 ps, while pure dephasing is negligible. Temperature increase leads to a significant shortening of T2 due to interaction with acoustic phonons. In contrast, the loss of coherence of the donor-bound B exciton (D0XB ) is significantly faster (T2=3.6 ps ) and governed by pure dephasing processes.
Electric moments in molecule interferometry
International Nuclear Information System (INIS)
Eibenberger, Sandra; Gerlich, Stefan; Arndt, Markus; Tuexen, Jens; Mayor, Marcel
2011-01-01
We investigate the influence of different electric moments on the shift and dephasing of molecules in a matter wave interferometer. Firstly, we provide a quantitative comparison of two molecules that are non-polar yet polarizable in their thermal ground state and that differ in their stiffness and response to thermal excitations. While C 25 H 20 is rather rigid, its larger derivative C 49 H 16 F 52 is additionally equipped with floppy side chains and vibrationally activated dipole moment variations. Secondly, we elucidate the role of a permanent electric dipole momentby contrasting the quantum interference pattern of a (nearly) non-polar and a polar porphyrin derivative. We find that a high molecular polarizability and even sizeable dipole moment fluctuations are still well compatible with high-contrast quantum interference fringes. The presence of permanent electric dipole moments, however, can lead to a dephasing and rapid degradation of the quantum fringe pattern already at moderate electric fields. This finding is of high relevance for coherence experiments with large organic molecules, which are generally equipped with strong electric moments.
Energy Technology Data Exchange (ETDEWEB)
Griesbeck, Michael
2012-11-22
Since many years there has been great effort to explore the spin dynamics in low-dimensional electron systems embedded in GaAs/AlGaAs based heterostructures for the purpose of quantum computation and spintronics applications. Advances in technology allow for the design of high quality and well-defined two-dimensional electron systems (2DES), which are perfectly suited for the study of the underlying physics that govern the dynamics of the electron spin system. In this work, spin dynamics in high-mobility 2DES is studied by means of the all-optical time-resolved Kerr/Faraday rotation technique. In (001)-grown 2DES, a strong in-plane spin dephasing anisotropy is studied, resulting from the interference of comparable Rashba and Dresselhaus contributions to the spin-orbit field (SOF). The dependence of this anisotropy on parameters like the confinement length of the 2DES, the sample temperature, as well as the electron density is demonstrated. Furthermore, coherent spin dynamics of an ensemble of ballistically moving electrons is studied without and within an applied weak magnetic field perpendicular to the sample plane, which forces the electrons to move on cyclotron orbits. Finally, strongly anisotropic spin dynamics is investigated in symmetric (110)-grown 2DES, using the resonant spin amplification method. Here, extremely long out-of-plane spin dephasing times can be achieved, in consequence of the special symmetry of the Dresselhaus SOF.
Coherent dynamics of excitons in a stack of self-assembled InAs quantum dots at 1.5-μm waveband
International Nuclear Information System (INIS)
Ishi-Hayase, J.; Akahane, K.; Yamamoto, N.; Kujiraoka, M.; Inoue, J.; Ema, K.; Tsuchiya, M.; Sasaki, M.
2006-01-01
We investigate the excitonic dephasing in a stack of self-assembled quantum dots (SAQDs) by using a four-wave-mixing (FWM) technique performed in the optical telecomm-fiber wavelength region at 6 K. A sample used in our experiment is a 150-layer stack of InAs SAQDs embedded in InGaAlAs grown on InP(3 1 1)B substrate fabricated by molecular beam epitaxy. By using a novel strain-controlled technique, the resonant wavelength of the exciton ground state (GS) ranges from 1.25 to 1.5 μm which is much longer than that in typical In(Ga)As SAQDs. In the weak excitation region, the intrinsic dephasing time of excitons at the excitation wavelength of 1.43 μm reaches 770 ps which is much longer than that in most SAQDs with the resonant wavelength of <1 μm. We also find a strong anisotoropy of the signal intensity with respect to the crystal axis attributed to the orientation of InP(3 1 1)B substrate and the elongated shape of QDs
Energy Technology Data Exchange (ETDEWEB)
Schwinkendorf, Jan-Patrick
2012-08-15
Plasma wakefields are a promising approach for the acceleration of electrons with ultrahigh (10 to 100 GV/m) electric fields. Nowadays, high-intensity laser pulses are routinely utilized to excite these large-amplitude plasma waves. However, several detrimental effects such as laser diffraction, electron-wake dephasing and laser depletion may terminate the acceleration process. Two of these phenomena can be mitigated or avoided by the application of capillary waveguides, e.g. fabricated out of sapphire for longevity. Capillaries may compensate for laser diffraction like a fiber and allow for the creation of tapered gas-density profiles working against the dephasing between the accelerating wave and the particles. Additionally, they offer the possibility of controlled particle injection. This thesis is reporting on the set up of a laser for fs-micromachining of capillaries of almost arbitrary shapes and a test stand for density-profile characterization. These devices will permit the creation of tailored gas-density profiles for controlled electron injection and acceleration inside plasma.
International Nuclear Information System (INIS)
Jiang Shuo; Luo Xiaoming; Chen Liqing; Ning Bo; Chen Shuai; Wang Jingyang; Zhong Zhiping; Pan Jianwei
2009-01-01
We report a prolonged coherence time of the collective spin wave of a thermal 87 Rb atomic ensemble in a paraffin-coated cell. The spin wave is prepared through a stimulated Raman process. The long coherence time is achieved by prolonging the lifetime of the spins with paraffin coating and minimize dephasing with optimal experimental configuration. The observation of the long-time-delayed-stimulated Stokes signal in the writing process suggests the prolonged lifetime of the prepared spins; a direct measurement of the decay of anti-Stokes signal in the reading process shows the coherence time is up to 300 μs after minimizing dephasing. This is 100 times longer than the reported coherence time in the similar experiments in thermal atomic ensembles based on the Duan-Lukin-Cirac-Zoller and its improved protocols. This prolonged coherence time sets the upper limit of the memory time in quantum repeaters based on such protocols, which is crucial for the realization of long-distance quantum communication. The previous reported fluorescence background in the writing process due to collision in a sample cell with buffer gas is also reduced in a cell without buffer gas.
Financial constraints for investors and the speed of adaptation: Are innovators special?
von Kalckreuth, Ulf
2004-01-01
This paper uses a large panel of survey data on German firms in the manufacturing sector to analyse the effects of financing constraints for investors in general and for innovative firms in particular. Survey data with information on financing conditions are potentially a valuable tool that avoids the Kaplan and Zingales (1997) critique on the use of cash flow sensitivities for the identification of financial constraints. Using the autumn and the spring wave of the Ifo Institute?s Investment ...
Roy, Chiranjeeb
In this thesis we study the role of nonradiative degrees of freedom on quantum optical properties of mesoscopic quantum dots placed in the structured electromagnetic reservoir of a photonic crystal. We derive a quantum theory of the role of acoustic and optical phonons in modifying the optical absorption lineshape, polarization dynamics, and population dynamics of a two-level atom (quantum dot) in the "colored" electromagnetic vacuum of a photonic band gap (PBG) material. This is based on a microscopic Hamiltonian describing both radiative and vibrational processes quantum mechanically. Phonon sidebands in an ordinary electromagnetic reservoir are recaptured in a simple model of optical phonons using a mean-field factorization of the atomic and lattice displacement operators. Our formalism is then used to treat the non-Markovian dynamics of the same system within the structured electromagnetic density of states of a photonic crystal. We elucidate the extent to which phonon-assisted decay limits the lifetime of a single photon-atom bound state and derive the modified spontaneous emission dynamics due to coupling to various phonon baths. We demonstrate that coherent interaction with undamped phonons can lead to enhanced lifetime of a photon-atom bound state in a PBG by (i) dephasing and reducing the transition electric dipole moment of the atom and (ii) reducing the quantum mechanical overlap of the state vectors of the excited and ground state (polaronic shift). This results in reduction of the steady-state atomic polarization but an increase in the fractionalized upper state population in the photon-atom bound state. We demonstrate, on the other hand, that the lifetime of the photon-atom bound state in a PBG is limited by the lifetime of phonons due to lattice anharmonicities (break-up of phonons into lower energy phonons) and purely nonradiative decay. We demonstrate how these additional damping effects limit the extent of the polaronic (Franck-Condon) shift of
Delineating incoherent non-Markovian dynamics using quantum coherence
Energy Technology Data Exchange (ETDEWEB)
Chanda, Titas, E-mail: titaschanda@hri.res.in; Bhattacharya, Samyadeb, E-mail: samyadebbhattacharya@hri.res.in
2016-03-15
We introduce a method of characterization of non-Markovianity using coherence of a system interacting with the environment. We show that under the allowed incoherent operations, monotonicity of a valid coherence measure is affected due to non-Markovian features of the system–environment evolution. We also define a measure to quantify non-Markovianity of the underlying dynamics based on the non-monotonic behavior of the coherence measure. We investigate our proposed non-Markovianity marker in the behavior of dephasing and dissipative dynamics for one and two qubit cases. We also show that our proposed measure captures the back-flow of information from the environment to the system and compatible with well known distinguishability criteria of non-Markovianity.
Low energy spread 100 MeV-1 GeV electron bunches from laser wakefield acceleration at LOASIS
International Nuclear Information System (INIS)
Geddes, C.G.R.; Esarey, E.; Michel, P.; Nagler, B.; Nakamura, K.; Plateau, G.R.; Schroeder, C.B.; Shadwick, B.A.; Toth, Cs.; Van Tilborg, J.; Leemans, W.P.; Hooker, S.M.; Gonsalves, A.J.; Michel, E.; Cary, J.R.; Bruhwiler, D.
2006-01-01
Experiments at the LOASIS laboratory of LBNL recently demonstrated production of 100 MeV electron beams with low energy spread and low divergence from laser wakefield acceleration. The radiation pressure of a 10 TW laser pulse guided over 10 diffraction ranges by a plasma density channel was used to drive an intense plasma wave (wakefield), producing acceleration gradients on the order of 100 GV/m in a mm-scale channel. Beam energy has now been increased from 100 to 1000 MeV by using a cm-scale guiding channel at lower density, driven by a 40TW laser, demonstrating the anticipated scaling to higher beam energies. Particle simulations indicate that the low energy spread beams were produced from self trapped electrons through the interplay of trapping, loading, and dephasing. Other experiments and simulations are also underway to control injection of particles into the wake, and hence improve beam quality and stability further
Dynamical correlation functions of the quadratic coupling spin-Boson model
Zheng, Da-Chuan; Tong, Ning-Hua
2017-06-01
The spin-boson model with quadratic coupling is studied using the bosonic numerical renormalization group method. We focus on the dynamical auto-correlation functions {C}O(ω ), with the operator \\hat{O} taken as {\\hat{{{σ }}}}x, {\\hat{{{σ }}}}z, and \\hat{X}, respectively. In the weak-coupling regime α qualitatively, showing enhanced dephasing at the spin flip point. Project supported by the National Key Basic Research Program of China (Grant No. 2012CB921704), the National Natural Science Foundation of China (Grant No. 11374362), the Fundamental Research Funds for the Central Universities, China, and the Research Funds of Renmin University of China (Grant No. 15XNLQ03).
Field-reversed bubble in deep plasma channels for high quality electron acceleration
Pukhov, A; Tueckmantel, T; Thomas, J; Yu, I; Kostyukov, Yu
2014-01-01
We study hollow plasma channels with smooth boundaries for laser-driven electron acceleration in the bubble regime. Contrary to the uniform plasma case, the laser forms no optical shock and no etching at the front. This increases the eﬀective bubble phase velocity and energy gain. The longitudinal ﬁeld has a plateau that allows for mono-energetic acceleration. We observe as low as 10−3 r.m.s. relative witness beam energy uncertainty in each cross-section and 0.3% total energy spread. By varying plasma density proﬁle inside a deep channel, the bubble ﬁelds can be adjusted to balance the laser depletion and dephasing lengths. Bubble scaling laws for the deep channel are derived. Ultra-short pancake-like laser pulses lead to the highest energies of accelerated electrons per Joule of laser pulse energy.
International Nuclear Information System (INIS)
Ye Tian-Yu
2015-01-01
At present, the anti-noise property and the information leakage resistant property are two great concerns for quantum dialogue (QD). In this paper, two anti-noise QD protocols without information leakage are presented by using the entanglement swapping technology for two logical Bell states. One works well over a collective-dephasing noise channel, while the other takes effect over a collective-rotation noise channel. The negative influence of noise is erased by using logical Bell states as the traveling quantum states. The problem of information leakage is avoided by swapping entanglement between two logical Bell states. In addition, only Bell state measurements are used for decoding, rather than four-qubit joint measurements. (paper)
International Nuclear Information System (INIS)
Weber, Christopher P.
2005-01-01
Spin diffusion in n-GaAs quantum wells, as measured by our optical transient-grating technique, is strongly suppressed relative to that of charge. Over a broad range of temperatures and dopings, the suppression of Ds relative to Dc agrees quantitatively with the prediction of ''spin Coulomb dra'' theory, which takes into account the exchange of spin in electron-electron collisions. Moreover, the spin-diffusion length, Ls, is a nearly constant 1 micrometer over the same range of T and n, despite Ds's varying by nearly two orders of magnitude. This constancy supports the D'yakonov-Perel'-Kachorovskii model of spin relaxation through interrupted precessional dephasing in the spin-orbit field
Dynamics of spins in semiconductor quantum wells under drift
International Nuclear Information System (INIS)
Idrish Miah, M.
2009-01-01
The dynamics of spins in semiconductor quantum wells under applied electric bias has been investigated by photoluminescence (PL) spectroscopy. The bias-dependent polarization of PL (P PL ) was measured at different temperatures. The P PL was found to decay with an enhancement of increasing the strength of the negative bias, with an exception occurred for a low value of the negative bias. The P PL was also found to depend on the temperature. The P PL in the presence of a transverse magnetic field was also studied. The results showed that P PL in the magnetic field oscillates under an applied bias, demonstrating that the dephasing of electron spin occurs during the drift transport in semiconductor quantum wells.
An environment-mediated quantum deleter
International Nuclear Information System (INIS)
Srikanth, R.; Banerjee, Subhashish
2007-01-01
Environment-induced decoherence presents a great challenge to realizing a quantum computer. We point out the somewhat surprising fact that decoherence can be useful, indeed necessary, for practical quantum computation, in particular, for the effective erasure of quantum memory in order to initialize the state of the quantum computer. The essential point behind the deleter is that the environment, by means of a dissipative interaction, furnishes a contractive map towards a pure state. We present a specific example of an amplitude damping channel provided by a two-level system's interaction with its environment in the weak Born-Markov approximation. This is contrasted with a purely dephasing, non-dissipative channel provided by a two-level system's interaction with its environment by means of a quantum nondemolition interaction. We point out that currently used state preparation techniques, for example using optical pumping, essentially perform as quantum deleters
Spatiotemporal control of laser intensity
Froula, Dustin H.; Turnbull, David; Davies, Andrew S.; Kessler, Terrance J.; Haberberger, Dan; Palastro, John P.; Bahk, Seung-Whan; Begishev, Ildar A.; Boni, Robert; Bucht, Sara; Katz, Joseph; Shaw, Jessica L.
2018-05-01
The controlled coupling of a laser to plasma has the potential to address grand scientific challenges1-6, but many applications have limited flexibility and poor control over the laser focal volume. Here, we present an advanced focusing scheme called a `flying focus', where a chromatic focusing system combined with chirped laser pulses enables a small-diameter laser focus to propagate nearly 100 times its Rayleigh length. Furthermore, the speed at which the focus moves (and hence the peak intensity) is decoupled from the group velocity of the laser. It can co- or counter-propagate along the laser axis at any velocity. Experiments validating the concept measured subluminal (-0.09c) to superluminal (39c) focal-spot velocities, generating a nearly constant peak intensity over 4.5 mm. Among possible applications, the flying focus could be applied to a photon accelerator7 to mitigate dephasing, facilitating the production of tunable XUV sources.
Theory of Excitonic Delocalization for Robust Vibronic Dynamics in LH2.
Caycedo-Soler, Felipe; Lim, James; Oviedo-Casado, Santiago; van Hulst, Niek F; Huelga, Susana F; Plenio, Martin B
2018-06-11
Nonlinear spectroscopy has revealed long-lasting oscillations in the optical response of a variety of photosynthetic complexes. Different theoretical models that involve the coherent coupling of electronic (excitonic) or electronic-vibrational (vibronic) degrees of freedom have been put forward to explain these observations. The ensuing debate concerning the relevance of either mechanism may have obscured their complementarity. To illustrate this balance, we quantify how the excitonic delocalization in the LH2 unit of Rhodopseudomonas acidophila purple bacterium leads to correlations of excitonic energy fluctuations, relevant coherent vibronic coupling, and importantly, a decrease in the excitonic dephasing rates. Combining these effects, we identify a feasible origin for the long-lasting oscillations observed in fluorescent traces from time-delayed two-pulse single-molecule experiments performed on this photosynthetic complex and use this approach to discuss the role of this complementarity in other photosynthetic systems.
Time-resolved measurements with intense ultrashort laser pulses: a 'molecular movie' in real time
International Nuclear Information System (INIS)
Rudenko, A; Ergler, Th; Feuerstein, B; Zrost, K; Schroeter, C D; Moshammer, R; Ullrich, J
2007-01-01
We report on the high-resolution multidimensional real-time mapping of H 2 + and D 2 + nuclear wave packets performed employing time-resolved three-dimensional Coulomb explosion imaging with intense laser pulses. Exploiting a combination of a 'reaction microscope' spectrometer and a pump-probe setup with two intense 6-7 fs laser pulses, we simultaneously visualize both vibrational and rotational motion of the molecule, and obtain a sequence of snapshots of the squared ro-vibrational wave function with time-step resolution of ∼ 0.3 fs, allowing us to reconstruct a real-time movie of the ultrafast molecular motion. We observe fast dephasing, or 'collapse' of the vibrational wave packet and its subsequent revival, as well as signatures of rotational excitation. For D 2 + we resolve also the fractional revivals resulting from the interference between the counter-propagating parts of the wave packet
International Nuclear Information System (INIS)
Chen, Shih-Hung; Chen, Liu
2013-01-01
The nonstationary oscillation of the gyrotron backward wave oscillator (gyro-BWO) with cylindrical interaction structure was studied utilizing both steady-state analyses and time-dependent simulations. Comparisons of the numerical results reveal that the gyro-BWO becomes nonstationary when the trailing field structure completely forms due to the dephasing energetic electrons. The backward propagation of radiated waves with a lower resonant frequency from the trailing field structure interferes with the main internal feedback loop, thereby inducing the nonstationary oscillation of the gyro-BWO. The nonstationary gyro-BWO exhibits the same spectral pattern of modulated oscillations with a constant frequency separation between the central frequency and sidebands throughout the whole system. The frequency separation is found to be scaled with the square root of the maximum field amplitude, thus further demonstrating that the nonstationary oscillation of the gyro-BWO is associated with the beam-wave resonance detuning
Enhanced Spin-Orbit Torque via Modulation of Spin Current Absorption
Qiu, Xuepeng
2016-11-18
The magnitude of spin-orbit torque (SOT), exerted to a ferromagnet (FM) from an adjacent heavy metal (HM), strongly depends on the amount of spin current absorbed in the FM. We exploit the large spin absorption at the Ru interface to manipulate the SOTs in HM/FM/Ru multilayers. While the FM thickness is smaller than its spin dephasing length of 1.2 nm, the top Ru layer largely boosts the absorption of spin currents into the FM layer and substantially enhances the strength of SOT acting on the FM. Spin-pumping experiments induced by ferromagnetic resonance support our conclusions that the observed increase in the SOT efficiency can be attributed to an enhancement of the spin-current absorption. A theoretical model that considers both reflected and transmitted mixing conductances at the two interfaces of FM is developed to explain the results.
Current-induced spin polarization in InGaAs and GaAs epilayers with varying doping densities
Luengo-Kovac, M.; Huang, S.; Del Gaudio, D.; Occena, J.; Goldman, R. S.; Raimondi, R.; Sih, V.
2017-11-01
The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InxGa1 -xAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the extrinsic contributions to the spin-polarization mechanism must be considered. Theoretical calculations based on a model that includes extrinsic contributions to the spin dephasing and the spin Hall effect, in addition to the intrinsic Rashba and Dresselhaus spin-orbit coupling, are found to reproduce the experimental finding that the crystal direction with the smaller net spin-orbit field has larger electrical spin generation efficiency and are used to predict how sample parameters affect the magnitude of the current-induced spin polarization.
Energy Technology Data Exchange (ETDEWEB)
Ullah, S.; Gusev, G. M.; Hernandez, F. G. G., E-mail: felixggh@if.usp.br [Instituto de Física, Universidade de São Paulo, Caixa Postal 66318, CEP 05315-970 São Paulo, SP (Brazil); Bakarov, A. K. [Institute of Semiconductor Physics and Novosibirsk State University, Novosibirsk 630090 (Russian Federation)
2016-06-07
We investigated the spin coherence of high-mobility two-dimensional electron gases confined in multilayer GaAs quantum wells. The dynamics of the spin polarization was optically studied using pump-probe techniques: time-resolved Kerr rotation and resonant spin amplification. For double and triple quantum wells doped beyond the metal-to-insulator transition, the spin-orbit interaction was tailored by the sample parameters of structural symmetry (Rashba constant), width, and electron density (Dresselhaus linear and cubic constants) which allow us to attain long dephasing times in the nanoseconds range. The determination of the scales, namely, transport scattering time, single-electron scattering time, electron-electron scattering time, and spin polarization decay time further supports the possibility of using n-doped multilayer systems for developing spintronic devices.
Non-Hermitian wave packet approximation for coupled two-level systems in weak and intense fields
Energy Technology Data Exchange (ETDEWEB)
Puthumpally-Joseph, Raiju; Charron, Eric [Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris-Sud, Université Paris-Saclay, F-91405 Orsay (France); Sukharev, Maxim [Science and Mathematics Faculty, College of Letters and Sciences, Arizona State University, Mesa, Arizona 85212 (United States)
2016-04-21
We introduce a non-Hermitian Schrödinger-type approximation of optical Bloch equations for two-level systems. This approximation provides a complete and accurate description of the coherence and decoherence dynamics in both weak and strong laser fields at the cost of losing accuracy in the description of populations. In this approach, it is sufficient to propagate the wave function of the quantum system instead of the density matrix, providing that relaxation and dephasing are taken into account via automatically adjusted time-dependent gain and decay rates. The developed formalism is applied to the problem of scattering and absorption of electromagnetic radiation by a thin layer comprised of interacting two-level emitters.
Geometric size effect on the extrinsic Gilbert damping in laterally confined magnetic structures
Energy Technology Data Exchange (ETDEWEB)
Song, Hyon-Seok [Department of Emerging Materials Science, DGIST, Daegu 42988 (Korea, Republic of); Lee, Kyeong-Dong [Department of Materials Science and Engineering, KAIST, Daejeon 34141 (Korea, Republic of); You, Chun-Yeol [Department of Physics, Inha University, Incheon 22212 (Korea, Republic of); Park, Byong-Guk [Department of Materials Science and Engineering, KAIST, Daejeon 34141 (Korea, Republic of); Hong, Jung-Il, E-mail: jihong@dgist.ac.kr [Department of Emerging Materials Science, DGIST, Daegu 42988 (Korea, Republic of); Research Centre for Emerging Materials, DGIST, Daegu 42988 (Korea, Republic of)
2016-05-15
We investigated spin dynamics in micron-length scale patterned thin films using the GPU-based micromagnetic simulation program. Spin precessional motion was induced by a Gaussian-pulse magnetic field. The effective Gilbert damping was examined by tracking the precessional motion of the spins, and we found that the damping constant depends on the size and shape of the pattern as well as the externally applied magnetic field. Additional extrinsic damping generated around the edge region was attributed to the dephasing effect between the fundamental spin wave and other spin wave modes. We find that the effect of extrinsic damping could be eliminated by proper adjustments of sample size, external bias field, position, and area of observation. - Highlights: • GPU based micromagnetic simulation of spin dynamics in the micropatterned ferromagnetic films. • Effect of edge regions of the pattern on the Gilbert damping behaviors. • Guide for the analyses of intrinsic magnetic damping in the micron scale patterned films.
Fluctuations in an established transmission in the presence of a complex environment
Savin, Dmitry V.; Richter, Martin; Kuhl, Ulrich; Legrand, Olivier; Mortessagne, Fabrice
2017-09-01
In various situations where wave transport is preeminent, like in wireless communication, a strong established transmission is present in a complex scattering environment. We develop a nonperturbative approach to describe emerging fluctuations which combines a transmitting channel and a chaotic background in a unified effective Hamiltonian. Modeling such a background by random matrix theory, we derive exact results for both transmission and reflection distributions at arbitrary absorption that is typically present in real systems. Remarkably, in such a complex scattering situation, the transport is governed by only two parameters: an absorption rate and the ratio of the so-called spreading width to the natural width of the transmission line. In particular, we find that the established transmission disappears sharply when this ratio exceeds unity. The approach exemplifies the role of the chaotic background in dephasing the deterministic scattering.
Spin-orbit coupling in ultracold Fermi gases of 173Yb atoms
Song, Bo; He, Chengdong; Hajiyev, Elnur; Ren, Zejian; Seo, Bojeong; Cai, Geyue; Amanov, Dovran; Zhang, Shanchao; Jo, Gyu-Boong
2017-04-01
Synthetic spin-orbit coupling (SOC) in cold atoms opens an intriguing new way to probe nontrivial topological orders beyond natural conditions. Here, we report the realization of the SOC physics both in a bulk system and in an optical lattice. First, we demonstrate two hallmarks induced from SOC in a bulk system, spin dephasing in the Rabi oscillation and asymmetric atomic distribution in the momentum space respectively. Then we describe the observation of non-trivial spin textures and the determination of the topological phase transition in a spin-dependent optical lattice dressed by the periodic Raman field. Furthermore, we discuss the quench dynamics between topological and trivial states by suddenly changing the band topology. Our work paves a new way to study non-equilibrium topological states in a controlled manner. Funded by Croucher Foundation and Research Grants Council (RGC) of Hong Kong (Project ECS26300014, GRF16300215, GRF16311516, and Croucher Innovation Grants).
Mullins, David
2017-09-01
Neutron imaging is typically used to image and reconstruct objects that are difficult to image using X-Ray imaging techniques. X-Ray absorption is primarily determined by the electron density of the material. This makes it difficult to image objects within materials that have high densities such as metal. However, the neutron scattering cross section primarily depends on the strong nuclear force, which varies somewhat randomly across the periodic table. In this project, an imaging technique known as dark field imaging using a far-field interferometer has been used to study a sample of granite. With this technique, interferometric phase images are generated. The dispersion of the microstructure of the sample dephases the beam, reducing the visibility. Collecting tomographic projections at different autocorrelation lengths (from 100 nanometers to 1.74 micrometers) essentially creates a 3D small angle scattering pattern, enabling mapping of how the microstructure is distributed throughout the sample.
Discontinuity in Fast Dynamics at the Glass Transition of ortho-Terphenyl.
Hoffman, David J; Fayer, Michael D
2017-11-16
The dynamics of the molecular glass former ortho-terphenyl through the glass transition were observed with two-dimensional infrared vibrational spectroscopy measurements of spectral diffusion using the small probe molecule phenylselenocyanate. Although the slow diffusive motions were not visible on the experimental time scale, a picosecond-scale exponential relaxation was observed at temperatures from above to well below the glass transition temperature. The characteristic time scale has a smooth temperature dependence from the liquid into the glass phase, but the range of vibrational frequencies the probe samples displayed a discontinuity at the glass transition temperature. Complementary pump-probe experiments associate the observed motion with density fluctuations. The key features of the dynamics are reproduced with a simple corrugated well potential energy surface model. In addition, the temperature dependence of the homogeneous vibrational dephasing was found to have a T 2 functional form, where T is the absolute temperature.
Weak antilocalization in Cd3As2 thin films.
Zhao, Bo; Cheng, Peihong; Pan, Haiyang; Zhang, Shuai; Wang, Baigeng; Wang, Guanghou; Xiu, Faxian; Song, Fengqi
2016-03-03
Recently, it has been theoretically predicted that Cd3As2 is a three dimensional Dirac material, a new topological phase discovered after topological insulators, which exhibits a linear energy dispersion in the bulk with massless Dirac fermions. Here, we report on the low-temperature magnetoresistance measurements on a ~50 nm-thick Cd3As2 film. The weak antilocalization under perpendicular magnetic field is discussed based on the two-dimensional Hikami-Larkin-Nagaoka (HLN) theory. The electron-electron interaction is addressed as the source of the dephasing based on the temperature-dependent scaling behavior. The weak antilocalization can be also observed while the magnetic field is parallel to the electric field due to the strong interaction between the different conductance channels in this quasi-two-dimensional film.
Trautmann, N.; Hauke, P.
2018-02-01
The transport of excitations governs fundamental properties of matter. Particularly rich physics emerges in the interplay between disorder and environmental noise, even in small systems such as photosynthetic biomolecules. Counterintuitively, noise can enhance coherent quantum transport, which has been proposed as a mechanism behind the high transport efficiencies observed in photosynthetic complexes. This effect has been called "environment-assisted quantum transport". Here, we propose a quantum simulation of the excitation transport in an open quantum network, taking advantage of the high controllability of current trapped-ion experiments. Our scheme allows for the controlled study of various different aspects of the excitation transfer, ranging from the influence of static disorder and interaction range, over the effect of Markovian and non-Markovian dephasing, to the impact of a continuous insertion of excitations. Our paper discusses experimental error sources and realistic parameters, showing that it can be implemented in state-of-the-art ion-chain experiments.
Spectrum of a one-atom laser in photonic crystals
International Nuclear Information System (INIS)
Florescu, Lucia
2006-01-01
The emission spectrum of a single-emitter laser in a photonic crystal is presented. We consider a coherently pumped two-level emitter strongly coupled to a high-quality microcavity engineered within a photonic crystal. We show that the cavity spectrum consists of both elastic and inelastic components, for which we derive analytical expressions. Our study reveals enhanced, spectrally narrower emission resulting from the radiation reservoir of the photonic crystal. The cavity field spectral characteristics are fundamentally distinct from those of a corresponding microcavity in ordinary vacuum. At high pump intensities and for large discontinuities in the photon density of states between Mollow spectral components of atomic resonance fluorescence, the emitted intensity originating from the elastic spectral component increases with the intensity of the pump and the elastic component dominates the spectrum. In the case of a vanishing photon density of states in the spectral range surrounding the lower Mollow sideband and no dipolar dephasing, the cavity spectrum is elastic
International Nuclear Information System (INIS)
Wang Xiaoting; Schirmer, Sophie G.; Bayat, Abolfazl; Bose, Sougato
2010-01-01
We discuss how to prepare an Ising chain in a GHZ state using a single global control field only. This model does not require the spins to be individually addressable and is applicable to quantum systems such as cold atoms in optical lattices, some liquid- or solid-state NMR experiments, and many nanoscale quantum structures. We show that GHZ states can always be reached asymptotically from certain easy-to-prepare initial states using adiabatic passage, and under certain conditions finite-time reachability can be ensured. To provide a reference useful for future experimental implementations, three different control strategies to achieve the objective--adiabatic passage, Lyapunov control, and optimal control--are compared, and their advantages and disadvantages discussed, in particular in the presence of realistic imperfections such as imperfect initial state preparation, system inhomogeneity, and dephasing.
Well-width dependence of the exciton-phonon scattering in thin InGaAs/GaAs single quantum wells
DEFF Research Database (Denmark)
Borri, Paola; Langbein, Wolfgang Werner; Hvam, Jørn Märcher
1998-01-01
We studied the temperature dependence of the exciton dephasing time in three In0.18Ga0.82As/GaAs single quantum wells, with well thickness Lw of 1, 1.5, and 2 nm, by degenerate time-integrated four-wave-mixing (TI-FWM) using 100-fs pulses in reflection geometry. The TI-FWM correlation traces...... clearly show an inhomogeneous broadening in all the samples at low temperature (5 K). We also show TI-FWM traces at the heavy-hole exciton transition in the 1.5-nm wide well, for resonant excitation at different temperatures. Around 95 K, the trace shows a decay that is no longer exponential for long...
Dynamics of spins in semiconductor quantum wells under drift
Energy Technology Data Exchange (ETDEWEB)
Idrish Miah, M., E-mail: m.miah@griffith.edu.a [Nanoscale Science and Technology Centre, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); School of Biomolecular and Physical Sciences, Griffith University, Nathan, Brisbane, QLD 4111 (Australia); Department of Physics, University of Chittagong, Chittagong 4331 (Bangladesh)
2009-09-15
The dynamics of spins in semiconductor quantum wells under applied electric bias has been investigated by photoluminescence (PL) spectroscopy. The bias-dependent polarization of PL (P{sub PL}) was measured at different temperatures. The P{sub PL} was found to decay with an enhancement of increasing the strength of the negative bias, with an exception occurred for a low value of the negative bias. The P{sub PL} was also found to depend on the temperature. The P{sub PL} in the presence of a transverse magnetic field was also studied. The results showed that P{sub PL} in the magnetic field oscillates under an applied bias, demonstrating that the dephasing of electron spin occurs during the drift transport in semiconductor quantum wells.
Capacity estimation and verification of quantum channels with arbitrarily correlated errors.
Pfister, Corsin; Rol, M Adriaan; Mantri, Atul; Tomamichel, Marco; Wehner, Stephanie
2018-01-02
The central figure of merit for quantum memories and quantum communication devices is their capacity to store and transmit quantum information. Here, we present a protocol that estimates a lower bound on a channel's quantum capacity, even when there are arbitrarily correlated errors. One application of these protocols is to test the performance of quantum repeaters for transmitting quantum information. Our protocol is easy to implement and comes in two versions. The first estimates the one-shot quantum capacity by preparing and measuring in two different bases, where all involved qubits are used as test qubits. The second verifies on-the-fly that a channel's one-shot quantum capacity exceeds a minimal tolerated value while storing or communicating data. We discuss the performance using simple examples, such as the dephasing channel for which our method is asymptotically optimal. Finally, we apply our method to a superconducting qubit in experiment.
Environment-induced decay of teleportation fidelity of the one-qubit state
Energy Technology Data Exchange (ETDEWEB)
Hu Mingliang, E-mail: mingliang0301@163.co [School of Science, Xi' an University of Posts and Telecommunications, Xi' an 710061 (China)
2011-05-23
The one-qubit teleportation protocol is reexamined when it is executed in the presence of various decohering environments. The results revealed that this quantum protocol is more robust under the influence of dephasing environment than those under the influence of dissipative or noisy environment. The environment may deprive the quantum advantage of teleportation over purely classical communication in a finite or infinite lifetime, which is dependent on the type of environment. Also we found that except entanglement, the purity of the entangled state resource is also crucial in determining the quality of the teleported state. - Highlights: Robustness of teleportation in the presence of various external environments. Environment deprives quantum advantage of teleportation over classical communication. A nonzero minimum entanglement is not always necessary for performing teleportation. Purity of the channel state is crucial in determining quality of the teleported state.
Kalampounias, Angelos G.; Papatheodorou, George N.
2018-06-01
Temperature dependent Raman spectra of boric oxide have been measured in a temperature range covering the glassy, supercooled and liquid state. The shift of the isotropic band assigned to boroxol rings relative to the anisotropic component upon heating the glass is measured and attributed to the Raman non-coincidence effect. The measured shift is associated with the competition between attraction and repulsion forces with increasing temperature. The relation of dephasing and orientational relaxation times to the non-coincidence effect of the condensed phases has been examined. We discuss our results in the framework of the current phenomenological status of the field in an attempt to separate the attraction and repulsion contributions corresponding to the observed non-coincidence effect.
Femtosecond Broadband Stimulated Raman Spectroscopy
International Nuclear Information System (INIS)
Lee, Soo-Y; Yoon, Sagwoon; Mathies, Richard A
2006-01-01
Femtosecond broadband stimulated Raman spectroscopy (FSRS) is a new technique where a narrow bandwidth picosecond Raman pump pulse and a red-shifted broadband femtosecond Stokes probe pulse (with or without time delay between the pulses) act on a sample to produce a high resolution Raman gain spectrum with high efficiency and speed, free from fluorescence background interference. It can reveal vibrational structural information and dynamics of stationary or transient states. Here, the quantum picture for femtosecond broadband stimulated Raman spectroscopy (FSRS) is used to develop the semiclassical coupled wave theory of the phenomenon and to derive an expression for the measurable Raman gain in FSRS. The semiclassical theory is applied to study the dependence of lineshapes in FSRS on the pump-probe time delay and to deduce vibrational dephasing times in cyclohexane in the ground state
Energy Technology Data Exchange (ETDEWEB)
Schubert, Alexander, E-mail: schubert@irsamc.ups-tlse.fr; Meier, Christoph [Laboratoire Collisions Agrégats et Réactivité, IRSAMC, UMR CNRS 5589, Université Paul Sabatier, 31062 Toulouse (France); Falvo, Cyril [Institut des Sciences Moléculaires d’Orsay (ISMO), CNRS, Univ. Paris-Sud, Université Paris-Saclay, 91405 Orsay (France)
2016-08-07
We present mixed quantum-classical simulations on relaxation and dephasing of vibrationally excited carbon monoxide within a protein environment. The methodology is based on a vibrational surface hopping approach treating the vibrational states of CO quantum mechanically, while all remaining degrees of freedom are described by means of classical molecular dynamics. The CO vibrational states form the “surfaces” for the classical trajectories of protein and solvent atoms. In return, environmentally induced non-adiabatic couplings between these states cause transitions describing the vibrational relaxation from first principles. The molecular dynamics simulation yields a detailed atomistic picture of the energy relaxation pathways, taking the molecular structure and dynamics of the protein and its solvent fully into account. Using the ultrafast photolysis of CO in the hemoprotein FixL as an example, we study the relaxation of vibrationally excited CO and evaluate the role of each of the FixL residues forming the heme pocket.
A non-linear theory for the bubble regime of plasma wake fields in tailored plasma channels
Thomas, Johannes
2016-01-01
We introduce a first full analytical bubble and blow-out model for a radially inhomogeneous plasma in a quasi-static approximation. For both cases we calculate the accelerating and the focusing fields. In our model we also assume a thin electron layer that surrounds the wake field and calculate the field configuration within. Our theory holds for arbitrary radial density profiles and reduces to known models in the limit of a homogeneous plasma. From a previous study of hollow plasma channels with smooth boundaries for laser-driven electron acceleration in the bubble regime we know that pancake-like laser pulses lead to highest electron energies [Pukhov et al, PRL 113, 245003 (2014)]. As it was shown, the bubble fields can be adjusted to balance the laser depletion and dephasing lengths by varying the plasma density profile inside a deep channel. Now we show why the radial fields in the vacuum part of a channel become defocussing.
Electron spin resonance and spin-valley physics in a silicon double quantum dot.
Hao, Xiaojie; Ruskov, Rusko; Xiao, Ming; Tahan, Charles; Jiang, HongWen
2014-05-14
Silicon quantum dots are a leading approach for solid-state quantum bits. However, developing this technology is complicated by the multi-valley nature of silicon. Here we observe transport of individual electrons in a silicon CMOS-based double quantum dot under electron spin resonance. An anticrossing of the driven dot energy levels is observed when the Zeeman and valley splittings coincide. A detected anticrossing splitting of 60 MHz is interpreted as a direct measure of spin and valley mixing, facilitated by spin-orbit interaction in the presence of non-ideal interfaces. A lower bound of spin dephasing time of 63 ns is extracted. We also describe a possible experimental evidence of an unconventional spin-valley blockade, despite the assumption of non-ideal interfaces. This understanding of silicon spin-valley physics should enable better control and read-out techniques for the spin qubits in an all CMOS silicon approach.
Measurement of complete and continuous Wigner functions for discrete atomic systems
Tian, Yali; Wang, Zhihui; Zhang, Pengfei; Li, Gang; Li, Jie; Zhang, Tiancai
2018-01-01
We measure complete and continuous Wigner functions of a two-level cesium atom in both a nearly pure state and highly mixed states. We apply the method [T. Tilma et al., Phys. Rev. Lett. 117, 180401 (2016), 10.1103/PhysRevLett.117.180401] of strictly constructing continuous Wigner functions for qubit or spin systems. We find that the Wigner function of all pure states of a qubit has negative regions and the negativity completely vanishes when the purity of an arbitrary mixed state is less than 2/3 . We experimentally demonstrate these findings using a single cesium atom confined in an optical dipole trap, which undergoes a nearly pure dephasing process. Our method can be applied straightforwardly to multi-atom systems for measuring the Wigner function of their collective spin state.
Diffraction of ultracold fermions by quantized light fields: Standing versus traveling waves
International Nuclear Information System (INIS)
Meiser, D.; Search, C.P.; Meystre, P.
2005-01-01
We study the diffraction of quantum-degenerate fermionic atoms off of quantized light fields in an optical cavity. We compare the case of a linear cavity with standing-wave modes to that of a ring cavity with two counterpropagating traveling wave modes. It is found that the dynamics of the atoms strongly depends on the quantization procedure for the cavity field. For standing waves, no correlations develop between the cavity field and the atoms. Consequently, standing-wave Fock states yield the same results as a classical standing wave field while coherent states give rise to a collapse and revivals in the scattering of the atoms. In contrast, for traveling waves the scattering results in quantum entanglement of the radiation field and the atoms. This leads to a collapse and revival of the scattering probability even for Fock states. The Pauli exclusion principle manifests itself as an additional dephasing of the scattering probability
Substantially Enhancing Quantum Coherence of Electrons in Graphene via Electron-Plasmon Coupling.
Cheng, Guanghui; Qin, Wei; Lin, Meng-Hsien; Wei, Laiming; Fan, Xiaodong; Zhang, Huayang; Gwo, Shangjr; Zeng, Changgan; Hou, J G; Zhang, Zhenyu
2017-10-13
The interplays between different quasiparticles in solids lay the foundation for a wide spectrum of intriguing quantum effects, yet how the collective plasmon excitations affect the quantum transport of electrons remains largely unexplored. Here we provide the first demonstration that when the electron-plasmon coupling is introduced, the quantum coherence of electrons in graphene is substantially enhanced with the quantum coherence length almost tripled. We further develop a microscopic model to interpret the striking observations, emphasizing the vital role of the graphene plasmons in suppressing electron-electron dephasing. The novel and transformative concept of plasmon-enhanced quantum coherence sheds new insight into interquasiparticle interactions, and further extends a new dimension to exploit nontrivial quantum phenomena and devices in solid systems.
The LHC dipole test control architecture
International Nuclear Information System (INIS)
Gorskaya, E.; Samojlov, V.; Raimondo, A.; Rijllart, A.
2003-01-01
The next large accelerator project at CERN is the Large Hadron Collider, which is foreseen to be installed in the existing LEP tunnel, and scheduled to be commissioned in 2007. For this project, 1200 15-metre long dipole magnets need to be tested at CERN in warm and cold conditions on dedicated test benches that are under development. The final LHC dipole series test set-up will consist of 12 benches organized in 6 clusters of two benches sharing the largest and most expensive devices. This sharing is made possible by a deliberate de-phasing of the tests among magnets, ensuring an optimum use of resources, such as cryogenics and power equipment, without limiting the total throughput. An offered two-level control architecture includes: 1) the Test 'Master' that drives the test for a cluster; 2) the Resource 'Manager' that allocates common devices and central resources. The implementation of this architecture is done in the LabVIEW environment
Correlation-induced suppression of decoherence in capacitively coupled Cooper-pair boxes
Hu, Xuedong; You, J. Q.; Nori, Franco
2005-03-01
Charge fluctuations from gate bias and background traps severely limit the performance of a charge qubit in a Cooper-pair box (CPB). Here we discuss an encoding approachootnotetextJ.Q. You, X.Hu, and F. Nori, cond-mat/0407423. to control the decoherence effects of these charge fluctuations using two strongly capacitively coupled CPBs. This coupled-box system has a low-decoherence subspace of two states, for which we calculate the dephasing and relaxation rates using a master equation approach. Our results show that the inter-box Coulomb correlation can significantly suppress decoherence of this two-level system by reducing the strength of the system-environment interaction, making it a promising candidate as a logical qubit, encoded using two CPBs.
Dissipative dynamics of superconducting hybrid qubit systems
International Nuclear Information System (INIS)
Montes, Enrique; Calero, Jesus M; Reina, John H
2009-01-01
We perform a theoretical study of composed superconducting qubit systems for the case of a coupled qubit configuration based on a hybrid qubit circuit made of both charge and phase qubits, which are coupled via a σ x x σ z interaction. We compute the system's eigen-energies in terms of the qubit transition frequencies and the strength of the inter-qubit coupling, and describe the sensitivity of the energy crossing/anti-crossing features to such coupling. We compute the hybrid system's dissipative dynamics for the cases of i) collective and ii) independent decoherence, whereby the system interacts with one common and two different baths of harmonic oscillators, respectively. The calculations have been performed within the Bloch-Redfield formalism and we report the solutions for the populations and the coherences of the system's reduced density matrix. The dephasing and relaxation rates are explicitly calculated as a function of the heat bath temperature.
Quantum jumps on Anderson attractors
Yusipov, I. I.; Laptyeva, T. V.; Ivanchenko, M. V.
2018-01-01
In a closed single-particle quantum system, spatial disorder induces Anderson localization of eigenstates and halts wave propagation. The phenomenon is vulnerable to interaction with environment and decoherence that is believed to restore normal diffusion. We demonstrate that for a class of experimentally feasible non-Hermitian dissipators, which admit signatures of localization in asymptotic states, quantum particle opts between diffusive and ballistic regimes, depending on the phase parameter of dissipators, with sticking about localization centers. In a diffusive regime, statistics of quantum jumps is non-Poissonian and has a power-law interval, a footprint of intermittent locking in Anderson modes. Ballistic propagation reflects dispersion of an ordered lattice and introduces the second timescale for jumps, resulting in non-nonmonotonous probability distribution. Hermitian dephasing dissipation makes localization features vanish, and Poissonian jump statistics along with normal diffusion are recovered.
Towards Long-Distance Atom-Photon Entanglement
International Nuclear Information System (INIS)
Rosenfeld, W.; Hocke, F.; Henkel, F.; Krug, M.; Volz, J.; Weber, M.; Weinfurter, H.
2008-01-01
We report the observation of entanglement between a single trapped atom and a single photon at remote locations. The degree of coherence of the entangled atom-photon pair is verified via appropriate local correlation measurements, after communicating the photon via an optical fiber link of 300 m length to a receiver 3.5 m apart. In addition, we measured the temporal evolution of the atomic density matrix after projecting the atom via a state measurement of the photon onto several well-defined spin states. We find that the state of the single atom dephases on a time scale of 150 μs, which represents an important step towards long-distance quantum networking with individual neutral atoms
Quantum speed limits in open system dynamics.
del Campo, A; Egusquiza, I L; Plenio, M B; Huelga, S F
2013-02-01
Bounds to the speed of evolution of a quantum system are of fundamental interest in quantum metrology, quantum chemical dynamics, and quantum computation. We derive a time-energy uncertainty relation for open quantum systems undergoing a general, completely positive, and trace preserving evolution which provides a bound to the quantum speed limit. When the evolution is of the Lindblad form, the bound is analogous to the Mandelstam-Tamm relation which applies in the unitary case, with the role of the Hamiltonian being played by the adjoint of the generator of the dynamical semigroup. The utility of the new bound is exemplified in different scenarios, ranging from the estimation of the passage time to the determination of precision limits for quantum metrology in the presence of dephasing noise.
Integrated nanoplasmonic quantum interfaces for room-temperature single-photon sources
Peyskens, Frédéric; Englund, Dirk; Chang, Darrick
2017-12-01
We describe a general analytical framework of a nanoplasmonic cavity-emitter system interacting with a dielectric photonic waveguide. Taking into account emitter quenching and dephasing, our model directly reveals the single-photon extraction efficiency η as well as the indistinguishability I of photons coupled into the waveguide mode. Rather than minimizing the cavity modal volume, our analysis predicts an optimum modal volume to maximize η that balances waveguide coupling and spontaneous emission rate enhancement. Surprisingly, our model predicts that near-unity indistinguishability is possible, but this requires a much smaller modal volume, implying a fundamental performance trade-off between high η and I at room temperature. Finally, we show that maximizing η I requires that the system has to be driven in the weak coupling regime because quenching effects and decreased waveguide coupling drastically reduce η in the strong coupling regime.
Nanosecond-timescale spin transfer using individual electrons in a quadruple-quantum-dot device
Energy Technology Data Exchange (ETDEWEB)
Baart, T. A.; Jovanovic, N.; Vandersypen, L. M. K. [QuTech and Kavli Institute of Nanoscience, Delft University of Technology, P.O. Box 5046, 2600 GA Delft (Netherlands); Reichl, C.; Wegscheider, W. [Solid State Physics Laboratory, ETH Zürich, 8093 Zürich (Switzerland)
2016-07-25
The ability to coherently transport electron-spin states between different sites of gate-defined semiconductor quantum dots is an essential ingredient for a quantum-dot-based quantum computer. Previous shuttles using electrostatic gating were too slow to move an electron within the spin dephasing time across an array. Here, we report a nanosecond-timescale spin transfer of individual electrons across a quadruple-quantum-dot device. Utilizing enhanced relaxation rates at a so-called hot spot, we can upper bound the shuttle time to at most 150 ns. While actual shuttle times are likely shorter, 150 ns is already fast enough to preserve spin coherence in, e.g., silicon based quantum dots. This work therefore realizes an important prerequisite for coherent spin transfer in quantum dot arrays.
Quantum information storage using tunable flux qubits
Energy Technology Data Exchange (ETDEWEB)
Steffen, Matthias; Brito, Frederico; DiVincenzo, David; Farinelli, Matthew; Keefe, George; Ketchen, Mark; Kumar, Shwetank; Milliken, Frank; Rothwell, Mary Beth; Rozen, Jim; Koch, Roger H, E-mail: msteffe@us.ibm.co [IBM Watson Research Center, Yorktown Heights, NY 10598 (United States)
2010-02-10
We present details and results for a superconducting quantum bit (qubit) design in which a tunable flux qubit is coupled strongly to a transmission line. Quantum information storage in the transmission line is demonstrated with a dephasing time of T{sub 2}approx2.5 mus. However, energy lifetimes of the qubit are found to be short (approx10 ns) and not consistent with predictions. Several design and material changes do not affect qubit coherence times. In order to determine the cause of these short coherence times, we fabricated standard flux qubits based on a design which was previously successfully used by others. Initial results show significantly improved coherence times, possibly implicating losses associated with the large size of our qubit. (topical review)
Physics at the FQMT'11 conference
Špička, V.; Nieuwenhuizen, Th M.; Keefe, P. D.
2012-11-01
This paper deals with the recent state of the art of the following topics presented at the FQMT'11 conference: foundations of quantum physics, quantum measurement; nonequilibrium quantum statistical physics; quantum thermodynamics; quantum measurement, entanglement and coherence; dissipation, dephasing, noise, and decoherence; quantum optics; macroscopic quantum behavior; e.g. cold atoms; Bose-Einstein condensates; physics of quantum computing and quantum information; mesoscopic, nano-electro-mechanical systems and nano-optical systems; spin systems and their dynamics; biological systems and molecular motors; and cosmology, gravitation and astrophysics. The lectures and discussions at the FQMT'11 conference, as well as the contributions to the related topical issue, reveal important themes for future development. The recent literature is included.
Thermal microwave states acting on a superconducting qubit
Energy Technology Data Exchange (ETDEWEB)
Goetz, Jan; Mueting, Miriam; Haeberlein, Max; Wulschner, Friedrich; Fischer, Michael; Deppe, Frank; Fedorov, Kirill; Huebl, Hans [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching (Germany); Physik-Department, TU Muenchen, 85748 Garching (Germany); Xie, Edwar; Eder, Peter; Deppe, Frank; Gross, Rudolf [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching (Germany); Physik-Department, TU Muenchen, 85748 Garching (Germany); Nanosystems Initiative Munich (NIM), Schellingstrasse 4, 80799 Muenchen (Germany); Marx, Achim [Walther-Meissner-Institut, Bayerische Akademie der Wissenschaften, 85748 Garching (Germany)
2016-07-01
We analyze the influence of broadband thermal states in the microwave regime on the coherence properties of a superconducting (transmon) qubit coupled to a transmission line resonator. We generate the thermal states inside the resonator by heating a 30 dB attenuator to emit blackbody radiation into a transmission line. In the absence of thermal fluctuations, the qubit coherence time is limited by relaxation. We find that the relaxation rate is almost unaffected by the presence of a thermal field inside the resonator. However, such states induce significant dephasing which increases quadratically with the number of thermal photons, whereas for a coherent population of the resonator, the increase shows a linear behavior. These results confirm the different photon statistics, being Poissonian for a coherent population and super-Poissonian for a thermal population of the resonator.
Light-Cone and Diffusive Propagation of Correlations in a Many-Body Dissipative System.
Bernier, Jean-Sébastien; Tan, Ryan; Bonnes, Lars; Guo, Chu; Poletti, Dario; Kollath, Corinna
2018-01-12
We analyze the propagation of correlations after a sudden interaction change in a strongly interacting quantum system in contact with an environment. In particular, we consider an interaction quench in the Bose-Hubbard model, deep within the Mott-insulating phase, under the effect of dephasing. We observe that dissipation effectively speeds up the propagation of single-particle correlations while reducing their coherence. In contrast, for two-point density correlations, the initial ballistic propagation regime gives way to diffusion at intermediate times. Numerical simulations, based on a time-dependent matrix product state algorithm, are supplemented by a quantitatively accurate fermionic quasiparticle approach providing an intuitive description of the initial dynamics in terms of holon and doublon excitations.
Quantum coding with finite resources
Tomamichel, Marco; Berta, Mario; Renes, Joseph M.
2016-01-01
The quantum capacity of a memoryless channel determines the maximal rate at which we can communicate reliably over asymptotically many uses of the channel. Here we illustrate that this asymptotic characterization is insufficient in practical scenarios where decoherence severely limits our ability to manipulate large quantum systems in the encoder and decoder. In practical settings, we should instead focus on the optimal trade-off between three parameters: the rate of the code, the size of the quantum devices at the encoder and decoder, and the fidelity of the transmission. We find approximate and exact characterizations of this trade-off for various channels of interest, including dephasing, depolarizing and erasure channels. In each case, the trade-off is parameterized by the capacity and a second channel parameter, the quantum channel dispersion. In the process, we develop several bounds that are valid for general quantum channels and can be computed for small instances. PMID:27156995
Slow and fast light in semiconductor waveguides
DEFF Research Database (Denmark)
Mørk, Jesper; Hansen, Per Lunnemann; Xue, Weiqi
2010-01-01
Investigations of slow and fast light effects in semiconductor waveguides entail interesting physics and point to a number of promising applications. In this review we give an overview of recent progress in the field, in particular focusing on the physical mechanisms of electromagnetically induced...... transparency and coherent population oscillations. While electromagnetically induced transparency has been the most important effect in realizing slowdown effects in atomic gasses, progress has been comparatively slow in semiconductors due to inherent problems of fast dephasing times and inhomogeneous...... broadening in quantum dots. The physics of electromagnetically induced transparency in semiconductors is discussed, emphasizing these limitations and recent suggestions for overcoming them. On the other hand, the mechanism of coherent population oscillations relies on wave mixing effects and is well suited...
Evolution of Nanowire Transmon Qubits and Their Coherence in a Magnetic Field
Luthi, F.; Stavenga, T.; Enzing, O. W.; Bruno, A.; Dickel, C.; Langford, N. K.; Rol, M. A.; Jespersen, T. S.; Nygârd, J.; Krogstrup, P.; DiCarlo, L.
2018-03-01
We present an experimental study of flux- and gate-tunable nanowire transmons with state-of-the-art relaxation time allowing quantitative extraction of flux and charge noise coupling to the Josephson energy. We evidence coherence sweet spots for charge, tuned by voltage on a proximal side gate, where first order sensitivity to switching two-level systems and background 1 /f noise is minimized. Next, we investigate the evolution of a nanowire transmon in a parallel magnetic field up to 70 mT, the upper bound set by the closing of the induced gap. Several features observed in the field dependence of qubit energy relaxation and dephasing times are not fully understood. Using nanowires with a thinner, partially covering Al shell will enable operation of these circuits up to 0.5 T, a regime relevant for topological quantum computation and other applications.
Non-Bloch decay of Rabi oscillations in liquid state NMR
Chakrabarti, Arnab; Bhattacharyya, Rangeet
2018-03-01
Rabi oscillations are known to exhibit non-Bloch behaviour in anisotropic media. In this letter, we report an experimental observation of non-Bloch decay of Rabi oscillations in isotropic liquid state NMR. To avoid the dephasing due to the radio-frequency inhomogeneities, we develop a modified version of the rotary echo protocol and use it to determine the decay rates of Rabi oscillations. We find that the measured decay rates are proportional to the square of the Rabi frequencies and the proportionality constant is of the order of tens of picoseconds. Further, we show that this non-Bloch nature of the decay rates becomes less prominent with increasing temperature. The implications of the presence of non-Bloch decay rates in liquid state NMR in the context of ensemble quantum computing are also discussed.
Ghaderzadeh, A.; Rahbari, S. H. Ebrahimnazhad; Phirouznia, A.
2018-03-01
In this study, Rashba coupling induced Aharonov-Casher effect in a graphene based nano ring is investigated theoretically. The graphene based nano ring is considered as a central device connected to semi-infinite graphene nano ribbons. In the presence of the Rashba spin-orbit interaction, two armchair shaped edge nano ribbons are considered as semi-infinite leads. The non-equilibrium Green's function approach is utilized to obtain the quantum transport characteristics of the system. The relaxation and dephasing mechanisms within the self-consistent Born approximation is scrutinized. The Lopez-Sancho method is also applied to obtain the self-energy of the leads. We unveil that the non-equilibrium current of the system possesses measurable Aharonov-Casher oscillations with respect to the Rashba coupling strength. In addition, we have observed the same oscillations in dilute impurity regimes in which amplitude of the oscillations is shown to be suppressed as a result of the relaxations.
Role of phase breaking processes on resonant spin transfer torque nano-oscillators
Sharma, Abhishek; Tulapurkar, Ashwin A.; Muralidharan, Bhaskaran
2018-05-01
Spin transfer torque nano-oscillators (STNOs) based on magnetoresistance and spin transfer torque effects find potential applications in miniaturized wireless communication devices. Using the non-coherent non-equilibrium Green's function spin transport formalism self-consistently coupled with the stochastic Landau-Lifshitz-Gilbert-Slonczewski's equation and the Poisson's equation, we elucidate the role of elastic phase breaking on the proposed STNO design featuring double barrier resonant tunneling. Demonstrating the immunity of our proposed design, we predict that despite the presence of elastic dephasing, the resonant tunneling magnetic tunnel junction structures facilitate oscillator designs featuring a large enhancement in microwave power up to 8μW delivered to a 50Ω load.
Suppressing relaxation in superconducting qubits by quasiparticle pumping.
Gustavsson, Simon; Yan, Fei; Catelani, Gianluigi; Bylander, Jonas; Kamal, Archana; Birenbaum, Jeffrey; Hover, David; Rosenberg, Danna; Samach, Gabriel; Sears, Adam P; Weber, Steven J; Yoder, Jonilyn L; Clarke, John; Kerman, Andrew J; Yoshihara, Fumiki; Nakamura, Yasunobu; Orlando, Terry P; Oliver, William D
2016-12-23
Dynamical error suppression techniques are commonly used to improve coherence in quantum systems. They reduce dephasing errors by applying control pulses designed to reverse erroneous coherent evolution driven by environmental noise. However, such methods cannot correct for irreversible processes such as energy relaxation. We investigate a complementary, stochastic approach to reducing errors: Instead of deterministically reversing the unwanted qubit evolution, we use control pulses to shape the noise environment dynamically. In the context of superconducting qubits, we implement a pumping sequence to reduce the number of unpaired electrons (quasiparticles) in close proximity to the device. A 70% reduction in the quasiparticle density results in a threefold enhancement in qubit relaxation times and a comparable reduction in coherence variability. Copyright © 2016, American Association for the Advancement of Science.
Observation of electron weak localization and correlation effects in disordered graphene
Institute of Scientific and Technical Information of China (English)
TAN ChangLing; TAN ZhenBing; MA Li; QU FanMing; YANG Fan; CHEN Jun; LIU GuangTong; YANG HaiFang; YANG ChangLi; LU Li
2009-01-01
We have studied the electron transport properties of a disordered graphene sample,where the disorder was intentionally strengthened by Ga+ ion irradiation.The magneto-conductance of the sample exhibits a typical two-dimensional electron weak localization behavior,with electron-electron interaction as the dominant dephasing mechanism.The absence of electron anti-weak localization in the sample implies strong intersublattice and/or intervalley scattering caused by the disorders.The temperature and bias-voltage dependencies of conductance clearly reveal the suppression of conductance at low ener-gies,indicating opening of a Coulomb gap due to electron-electron interaction in the disordered gra-phene sample.
Phonon effects on the radiative recombination of excitons in double quantum dots
Karwat, Paweł; Sitek, Anna; Machnikowski, Paweł
2011-11-01
We study theoretically the radiative recombination of excitons in double quantum dots in the presence of carrier-phonon coupling. We show that the phonon-induced pure dephasing effects and transitions between the exciton states strongly modify the spontaneous emission process and make it sensitive to temperature, which may lead to nonmonotonic temperature dependence of the time-resolved luminescence. We show also that, under specific resonance conditions, the biexcitonic interband polarization can be coherently transferred to the excitonic one, leading to an extended lifetime of the total coherent polarization, which is reflected in the nonlinear optical spectrum of the system. We study the stability of this effect against phonon-induced decoherence.
Unusual metal-insulator transition in disordered ferromagnetic films
International Nuclear Information System (INIS)
Muttalib, K.A.; Wölfle, P.; Misra, R.; Hebard, A.F.
2012-01-01
We present a theoretical interpretation of recent data on the conductance near and farther away from the metal-insulator transition in thin ferromagnetic Gd films of thickness b≈2-10 nm. For increasing sheet resistances a dimensional crossover takes place from d=2 to d=3 dimensions, since the large phase relaxation rate caused by scattering of quasiparticles off spin wave excitations renders the dephasing length L φ ≲b at strong disorder. The conductivity data in the various regimes obey fractional power-law or logarithmic temperature dependence. One observes weak localization and interaction induced corrections at weaker disorder. At strong disorder, near the metal-insulator transition, the data show scaling and collapse onto two scaling curves for the metallic and insulating regimes. We interpret this unusual behavior as proof of two distinctly different correlation length exponents on both sides of the transition.
Origin and Reduction of 1/f Magnetic Flux Noise in Superconducting Devices
Energy Technology Data Exchange (ETDEWEB)
Kumar, P.; Sendelbach, S.; Beck, M. A.; Freeland, J. W.; Wang, Zhe; Wang, Hui; Yu, Clare C.; Wu, R. Q.; Pappas, D. P.; McDermott, R.
2016-10-01
Magnetic flux noise is a dominant source of dephasing and energy relaxation in superconducting qubits. The noise power spectral density varies with frequency as 1=fα, with α ≲ 1, and spans 13 orders of magnitude. Recent work indicates that the noise is from unpaired magnetic defects on the surfaces of the superconducting devices. Here, we demonstrate that adsorbed molecular O2 is the dominant contributor to magnetism in superconducting thin films. We show that this magnetism can be reduced by appropriate surface treatment or improvement in the sample vacuum environment. We observe a suppression of static spin susceptibility by more than an order of magnitude and a suppression of 1=f magnetic flux noise power spectral density of up to a factor of 5. These advances open the door to the realization of superconducting qubits with improved quantum coherence.
Origin and Reduction of 1 /f Magnetic Flux Noise in Superconducting Devices
Kumar, P.; Sendelbach, S.; Beck, M. A.; Freeland, J. W.; Wang, Zhe; Wang, Hui; Yu, Clare C.; Wu, R. Q.; Pappas, D. P.; McDermott, R.
2016-10-01
Magnetic flux noise is a dominant source of dephasing and energy relaxation in superconducting qubits. The noise power spectral density varies with frequency as 1 /fα, with α ≲1 , and spans 13 orders of magnitude. Recent work indicates that the noise is from unpaired magnetic defects on the surfaces of the superconducting devices. Here, we demonstrate that adsorbed molecular O2 is the dominant contributor to magnetism in superconducting thin films. We show that this magnetism can be reduced by appropriate surface treatment or improvement in the sample vacuum environment. We observe a suppression of static spin susceptibility by more than an order of magnitude and a suppression of 1 /f magnetic flux noise power spectral density of up to a factor of 5. These advances open the door to the realization of superconducting qubits with improved quantum coherence.
Quantum feedback for rapid state preparation in the presence of control imperfections
International Nuclear Information System (INIS)
Combes, Joshua; Wiseman, Howard M
2011-01-01
Quantum feedback control protocols can improve the operation of quantum devices. Here we examine the performance of a purification protocol when there are imperfections in the controls. The ideal feedback protocol produces an x-eigenstate from a mixed state in the minimum time, and is known as rapid state preparation. The imperfections we examine include time delays in the feedback loop, finite strength feedback, calibration errors and inefficient detection. We analyse these imperfections using the Wiseman-Milburn feedback master equation and related formalism. We find that the protocol is most sensitive to time delays in the feedback loop. For systems with slow dynamics, however, our analysis suggests that inefficient detection would be the bigger problem. We also show how system imperfections, such as dephasing and damping, can be included in a model via the feedback master equation.
Plasmonic tunnel junctions for single-molecule redox chemistry.
de Nijs, Bart; Benz, Felix; Barrow, Steven J; Sigle, Daniel O; Chikkaraddy, Rohit; Palma, Aniello; Carnegie, Cloudy; Kamp, Marlous; Sundararaman, Ravishankar; Narang, Prineha; Scherman, Oren A; Baumberg, Jeremy J
2017-10-20
Nanoparticles attached just above a flat metallic surface can trap optical fields in the nanoscale gap. This enables local spectroscopy of a few molecules within each coupled plasmonic hotspot, with near thousand-fold enhancement of the incident fields. As a result of non-radiative relaxation pathways, the plasmons in such sub-nanometre cavities generate hot charge carriers, which can catalyse chemical reactions or induce redox processes in molecules located within the plasmonic hotspots. Here, surface-enhanced Raman spectroscopy allows us to track these hot-electron-induced chemical reduction processes in a series of different aromatic molecules. We demonstrate that by increasing the tunnelling barrier height and the dephasing strength, a transition from coherent to hopping electron transport occurs, enabling observation of redox processes in real time at the single-molecule level.
Modeling of low- and high-frequency noise by slow and fast fluctuators
Nesterov, Alexander I.; Berman, Gennady P.
2012-05-01
We study the dynamics of dephasing in a quantum two-level system by modeling both 1/f and high-frequency noise by random telegraph processes. Our approach is based on a so-called spin-fluctuator model in which a noisy environment is modeled by a large number of fluctuators. In the continuous limit we obtain an effective random process (ERP) that is described by a distribution function of the fluctuators. In a simplified model, we reduce the ERP to the two (slow and fast) ensembles of fluctuators. Using this model, we study decoherence in a superconducting flux qubit and we compare our theoretical results with the available experimental data. We demonstrate good agreement of our theoretical predictions with the experiments. Our approach can be applied to many quantum systems, such as biological complexes, semiconductors, superconducting, and spin qubits, where the effects of interaction with the environment are essential.
Experimental decoherence in molecule interferometry
International Nuclear Information System (INIS)
Hackermueller, L.; Hornberger, K.; Stibor, A.; Zeilinger, A.; Arndt, M.; Kiesewetter, G.
2005-01-01
Full text: We present three mechanisms of decoherence that occur quite naturally in matter wave interferometer with large molecules. One way molecules can lose coherence is through collision with background gas particles. We observe a loss of contrast with increasing background pressure for various types of gases. We can understand this phenomenon quantitatively with a new model for collisional decoherence which corrects older models by a factor of 2 π;. The second experiment studies the thermal emission of photons related to the high internal energy of the interfering molecules. When sufficiently many or sufficiently short photons are emitted inside the interferometer, the fringe contrast is lost. We can continuously vary the temperature of the molecules and compare the loss of contrast with a model based on decoherence theory. Again we find good quantitative agreement. A third mechanism that influences our interference pattern is dephasing due to vibrations of the interference gratings. By adding additional vibrations we study this effect in more detail. (author)
Single-particle model of a strongly driven, dense, nanoscale quantum ensemble
DiLoreto, C. S.; Rangan, C.
2018-01-01
We study the effects of interatomic interactions on the quantum dynamics of a dense, nanoscale, atomic ensemble driven by a strong electromagnetic field. We use a self-consistent, mean-field technique based on the pseudospectral time-domain method and a full, three-directional basis to solve the coupled Maxwell-Liouville equations. We find that interatomic interactions generate a decoherence in the state of an ensemble on a much faster time scale than the excited-state lifetime of individual atoms. We present a single-particle model of the driven, dense ensemble by incorporating interactions into a dephasing rate. This single-particle model reproduces the essential physics of the full simulation and is an efficient way of rapidly estimating the collective dynamics of a dense ensemble.
Theory of electron spin echoes in solids
Asadullina, N Y; Asadullin, Y Y
2002-01-01
We propose modified Bloch equations (MBEs) with specific power-dependent relaxation and dispersion parameters characteristic for two-pulse excitation and when the magnetic dipole-dipole interactions in the electron spin system control the dephasing. We discriminate between the 'active' (excited by both pulses) and 'passive' (excited by the second pulse only) spins: it is shown that the 'active' spins participate in a new effect, an active spin frequency modulation effect giving rise to the power-dependent dispersion and multiple electron spin echoes (ESEs); the 'passive' spins contribute to the power-dependent relaxation. The MBEs are solved and a general expression for the two-pulse ESEs is obtained. Detailed numerical analysis of this expression gives results in good quantitative agreement with the recent experiments on the two-pulse ESEs at conventional low applied fields. The developed theory is applied also to high field ESEs, which are promising for future investigations. On the basis of published resul...
Filter-design perspective applied to dynamical decoupling of a multi-qubit system
International Nuclear Information System (INIS)
Su Zhikun; Jiang Shaoji
2012-01-01
We employ the filter-design perspective and derive the filter functions according to nested Uhrig dynamical decoupling (NUDD) and symmetric dynamical decoupling (SDD) in the pure-dephasing spin-boson model with N qubits. The performances of NUDD and SDD are discussed in detail for a two-qubit system. The analysis shows that (i) SDD outperforms NUDD for the bath with a soft cutoff while NUDD approaches SDD as the cutoff becomes harder; (ii) if the qubits are coupled to a common reservoir, SDD helps to protect the decoherence-free subspace while NUDD destroys it; (iii) when the imperfect control pulses with finite width are considered, NUDD is affected in both the high-fidelity regime and coherence time regime while SDD is affected in the coherence time regime only. (paper)
Dynamic localization in quantum dots: Analytical theory
International Nuclear Information System (INIS)
Basko, D.M.; Skvortsov, M.A.; Kravtsov, V.E.
2003-02-01
We analyze the response of a complex quantum-mechanical system (e.g., a quantum dot) to a time-dependent perturbation φ(t). Assuming the dot to be described by random matrix theory for GOE we find the quantum correction to the energy absorption rate as a function of the dephasing time t φ . If φ(t) is a sum of d harmonics with incommensurate frequencies, the correction behaves similarly to that to the conductivity δσ d (t φ ) in the d-dimensional Anderson model of the orthogonal symmetry class. For a generic periodic perturbation the leading quantum correction is absent as in the systems of the unitary symmetry class, unless φ(-t+τ)=φ(t+τ) for some τ, which falls into the quasi-1d orthogonal universality class. (author)
Symmetry-protected coherent relaxation of open quantum systems
van Caspel, Moos; Gritsev, Vladimir
2018-05-01
We compute the effect of Markovian bulk dephasing noise on the staggered magnetization of the spin-1/2 XXZ Heisenberg chain, as the system evolves after a Néel quench. For sufficiently weak system-bath coupling, the unitary dynamics are found to be preserved up to a single exponential damping factor. This is a consequence of the interplay between PT symmetry and weak symmetries, which strengthens previous predictions for PT -symmetric Liouvillian dynamics. Requirements are a nondegenerate PT -symmetric generator of time evolution L ̂, a weak parity symmetry, and an observable that is antisymmetric under this parity transformation. The spectrum of L ̂ then splits up into symmetry sectors, yielding the same decay rate for all modes that contribute to the observable's time evolution. This phenomenon may be realized in trapped ion experiments and has possible implications for the control of decoherence in out-of-equilibrium many-body systems.
International Nuclear Information System (INIS)
Loock, Peter van; Nemoto, Kae; Munro, William J.; Raynal, Philippe; Luetkenhaus, Norbert
2006-01-01
We discuss the problem of implementing generalized measurements [positive operator-valued measures (POVMs)] with linear optics, either based upon a static linear array or including conditional dynamics. In our approach, a given POVM shall be identified as a solution to an optimization problem for a chosen cost function. We formulate a general principle: the implementation is only possible if a linear-optics circuit exists for which the quantum mechanical optimum (minimum) is still attainable after dephasing the corresponding quantum states. The general principle enables us, for instance, to derive a set of necessary conditions for the linear-optics implementation of the POVM that realizes the quantum mechanically optimal unambiguous discrimination of two pure nonorthogonal states. This extends our previous results on projection measurements and the exact discrimination of orthogonal states
International Nuclear Information System (INIS)
Wang Chao; Liu Jian-Wei; Shang Tao; Chen Xiu-Bo; Bi Ya-Gang
2015-01-01
This study proposes two novel fault tolerant deterministic secure quantum communication (DSQC) schemes resistant to collective noise using logical Bell states. Either DSQC scheme is constructed based on a new coding function, which is designed by exploiting the property of the corresponding logical Bell states immune to collective-dephasing noise and collective-rotation noise, respectively. The secret message can be encoded by two simple unitary operations and decoded by merely performing Bell measurements, which can make the proposed scheme more convenient in practical applications. Moreover, the strategy of one-step quanta transmission, together with the technique of decoy logical qubits checking not only reduces the influence of other noise existing in a quantum channel, but also guarantees the security of the communication between two legitimate users. The final analysis shows that the proposed schemes are feasible and robust against various well-known attacks over the collective noise channel. (paper)
Energy Technology Data Exchange (ETDEWEB)
Weber, Christopher Phillip [Univ. of California, Berkeley, CA (United States)
2005-01-01
Spin diffusion in n-GaAs quantum wells, as measured by our optical transient-grating technique, is strongly suppressed relative to that of charge. Over a broad range of temperatures and dopings, the suppression of Ds relative to Dc agrees quantitatively with the prediction of ''spin Coulomb dra'' theory, which takes into account the exchange of spin in electron-electron collisions. Moreover, the spin-diffusion length, Ls, is a nearly constant 1 micrometer over the same range of T and n, despite Ds's varying by nearly two orders of magnitude. This constancy supports the D'yakonov-Perel'-Kachorovskii model of spin relaxation through interrupted precessional dephasing in the spin-orbit field.
Fault-Tolerate Three-Party Quantum Secret Sharing over a Collective-Noise Channel
International Nuclear Information System (INIS)
Li Chun-Yan; Li Yan-Song
2011-01-01
We present a fault-tolerate three-party quantum secret sharing (QSS) scheme over a collective-noise channel. Decoherence-free subspaces are used to tolerate two noise modes, a collective-dephasing channel and a collective-rotating channel, respectively. In this scheme, the boss uses two physical qubits to construct a logical qubit which acts as a quantum channel to transmit one bit information to her two agents. The agents can get the information of the private key established by the boss only if they collaborate. The boss Alice encodes information with two unitary operations. Only single-photon measurements are required to rebuilt Alice's information and detect the security by the agents Bob and Charlie, not Bell-state measurements. Moreover, Almost all of the photons are used to distribute information, and its success efficiency approaches 100% in theory. (general)
Mitsumori, Yasuyoshi; Matsuura, Shimpei; Uchiyama, Shoichi; Saito, Kentarao; Edamatsu, Keiichi; Nakayama, Masaaki; Ajiki, Hiroshi
2018-04-01
We study the biexciton relaxation process in CuCl films ranging from 6 to 200 nm. The relaxation time is measured as the dephasing time and the lifetime. We observe a unique thickness dependence of the biexciton relaxation time and also obtain an ultrafast relaxation time with a timescale as short as 100 fs, while the exciton lifetime monotonically decreases with increasing thickness. By analyzing the exciton-photon coupling energy for a surface polariton, we theoretically calculate the biexciton relaxation time as a function of the thickness. The calculated dependence qualitatively reproduces the observed relaxation time, indicating that the biexciton dissociation into a surface polariton pair is one of the major biexciton relaxation processes.
DEFF Research Database (Denmark)
Denning, Emil Vosmar; Iles-Smith, Jake; McCutcheon, Dara P. S.
2017-01-01
Multiphoton entangled states are a crucial resource for many applications inquantum information science. Semiconductor quantum dots offer a promising route to generate such states by mediating photon-photon correlations via a confinedelectron spin, but dephasing caused by the host nuclear spin...... environment typically limits coherence (and hence entanglement) between photons to the spin T2* time of a few nanoseconds. We propose a protocol for the deterministic generation of multiphoton entangled states that is inherently robust against the dominating slow nuclear spin environment fluctuations, meaning...... that coherence and entanglement is instead limited only by the much longer spin T2 time of microseconds. Unlike previous protocols, the present schemeallows for the generation of very low error probability polarisation encoded three-photon GHZ states and larger entangled states, without the need for spin echo...
Belykh, V. V.; Kavokin, K. V.; Yakovlev, D. R.; Bayer, M.
2017-12-01
The evolution of the electron spin dynamics as consequence of carrier delocalization in n -type GaAs is investigated by the recently developed extended pump-probe Kerr/Faraday rotation spectroscopy. We find that isolated electrons localized on donors demonstrate a prominent difference between the longitudinal and transverse spin relaxation rates in a magnetic field, which is almost absent in the metallic phase. The inhomogeneous transverse dephasing time T2* of the spin ensemble strongly increases upon electron delocalization as a result of motional narrowing that can be induced by increasing either the donor concentration or the temperature. An unexpected relation between T2* and the longitudinal spin relaxation time T1 is found, namely, that their product is about constant, as explained by the magnetic field effect on the spin diffusion. We observe a two-stage longitudinal spin relaxation, which suggests the establishment of spin temperature in the system of exchange-coupled donor-bound electrons.
Puebla, Ricardo; Casanova, Jorge; Plenio, Martin B.
2018-03-01
The dynamics of the quantum Rabi model (QRM) in the deep strong coupling regime is theoretically analyzed in a trapped-ion set-up. Recognizably, the main hallmark of this regime is the emergence of collapses and revivals, whose faithful observation is hindered under realistic magnetic dephasing noise. Here, we discuss how to attain a faithful implementation of the QRM in the deep strong coupling regime which is robust against magnetic field fluctuations and at the same time provides a large tunability of the simulated parameters. This is achieved by combining standing wave laser configuration with continuous dynamical decoupling. In addition, we study the role that amplitude fluctuations play to correctly attain the QRM using the proposed method. In this manner, the present work further supports the suitability of continuous dynamical decoupling techniques in trapped-ion settings to faithfully realize different interacting dynamics.
Collapse and revival in holographic quenches
International Nuclear Information System (INIS)
Silva, Emilia da; Lopez, Esperanza; Mas, Javier; Serantes, Alexandre
2015-01-01
We study holographic models related to global quantum quenches in finite size systems. The holographic set up describes naturally a CFT, which we consider on a circle and a sphere. The enhanced symmetry of the conformal group on the circle motivates us to compare the evolution in both cases. Depending on the initial conditions, the dual geometry exhibits oscillations that we holographically interpret as revivals of the initial field theory state. On the sphere, this only happens when the energy density created by the quench is small compared to the system size. However on the circle considerably larger energy densities are compatible with revivals. Two different timescales emerge in this latter case. A collapse time, when the system appears to have dephased, and the revival time, when after rephasing the initial state is partially recovered. The ratio of these two times depends upon the initial conditions in a similar way to what is observed in some experimental setups exhibiting collapse and revivals.
Sine-squared shifted pulses for recoupling interactions in solid-state NMR
Jain, Mukul G.; Rajalakshmi, G.; Equbal, Asif; Mote, Kaustubh R.; Agarwal, Vipin; Madhu, P. K.
2017-06-01
Rotational-Echo DOuble-Resonance (REDOR) is a versatile experiment for measuring internuclear distance between two heteronuclear spins in solid-state NMR. At slow to intermediate magic-angle spinning (MAS) frequencies, the measurement of distances between strongly coupled spins is challenging due to rapid dephasing of magnetisation. This problem can be remedied by employing the pulse-shifted version of REDOR known as Shifted-REDOR (S-REDOR) that scales down the recoupled dipolar coupling. In this study, we propose a new variant of the REDOR sequence where the positions of the π pulses are determined by a sine-squared function. This new variant has scaling properties similar to S-REDOR. We use theory, numerical simulations, and experiments to compare the dipolar recoupling efficiencies and the experimental robustness of the three REDOR schemes. The proposed variant has advantages in terms of radiofrequency field requirements at fast MAS frequencies.
Self-referenced coherent diffraction x-ray movie of Ångstrom- and femtosecond-scale atomic motion
International Nuclear Information System (INIS)
Glownia, J. M.; Natan, A.; Cryan, J. P.; Hartsock, R.; Kozina, M.
2016-01-01
Time-resolved femtosecond x-ray diffraction patterns from laser-excited molecular iodine are used to create a movie of intramolecular motion with a temporal and spatial resolution of 30 fs and 0.3 Å. This high fidelity is due to interference between the nonstationary excitation and the stationary initial charge distribution. The initial state is used as the local oscillator for heterodyne amplification of the excited charge distribution to retrieve real-space movies of atomic motion on ångstrom and femtosecond scales. This x-ray interference has not been employed to image internal motion in molecules before. In conclusion, coherent vibrational motion and dispersion, dissociation, and rotational dephasing are all clearly visible in the data, thereby demonstrating the stunning sensitivity of heterodyne methods.
Phase-coherent electron transport in (Zn, Al)Ox thin films grown by atomic layer deposition
Saha, D.; Misra, P.; Ajimsha, R. S.; Joshi, M. P.; Kukreja, L. M.
2014-11-01
A clear signature of disorder induced quantum-interference phenomena leading to phase-coherent electron transport was observed in (Zn, Al)Ox thin films grown by atomic layer deposition. The degree of static-disorder was tuned by varying the Al concentration through periodic incorporation of Al2O3 sub-monolayer in ZnO. All the films showed small negative magnetoresistance due to magnetic field suppressed weak-localization effect. The temperature dependence of phase-coherence length ( l φ ∝ T - 3 / 4 ), as extracted from the magnetoresistance measurements, indicated electron-electron scattering as the dominant dephasing mechanism. The persistence of quantum-interference at relatively higher temperatures up to 200 K is promising for the realization of ZnO based phase-coherent electron transport devices.
Phase-coherent electron transport in (Zn, Al)O{sub x} thin films grown by atomic layer deposition
Energy Technology Data Exchange (ETDEWEB)
Saha, D., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in; Misra, P., E-mail: sahaphys@gmail.com, E-mail: pmisra@rrcat.gov.in; Ajimsha, R. S.; Joshi, M. P.; Kukreja, L. M. [Laser Materials Processing Division, Raja Ramanna Centre for Advanced Technology, Indore 452 013 (India)
2014-11-24
A clear signature of disorder induced quantum-interference phenomena leading to phase-coherent electron transport was observed in (Zn, Al)O{sub x} thin films grown by atomic layer deposition. The degree of static-disorder was tuned by varying the Al concentration through periodic incorporation of Al{sub 2}O{sub 3} sub-monolayer in ZnO. All the films showed small negative magnetoresistance due to magnetic field suppressed weak-localization effect. The temperature dependence of phase-coherence length (l{sub φ}∝T{sup −3/4}), as extracted from the magnetoresistance measurements, indicated electron-electron scattering as the dominant dephasing mechanism. The persistence of quantum-interference at relatively higher temperatures up to 200 K is promising for the realization of ZnO based phase-coherent electron transport devices.
Dynamics for CH3F and CD3F isolated in rare gas solids
International Nuclear Information System (INIS)
Jones, L.H.; Swanson, B.I.
1982-01-01
High resolution infrared spectra have been obtained for CH 3 F and CD 3 F in argon and krypton matrices from 3 to 39 K. Low-temperature spectra show structure indicative of two stable monomer sites. As temperature is raised, the structure collapses to give symmetric peaks for each mode. The line shapes and their broadening with temperature show large dependence on the modes, isotope, and host matrix. On the basis of the absence of rovibrational structure and the very different line shapes for the various modes, we conclude that free or hindered rotation does not contribute to the absorption lines of methyl fluoride in argon or krypton matrices below 40 K. The mode dependent line broadening with increasing temperatures has been attributed to vibrational dephasing involving low energy site local phonon modes. Implications with regard to vibrational energy relaxation, which is currently thought to be dominated by a vibration to rotation energy transfer, are discussed
Theoretical model of intravascular paramagnetic tracers effect on tissue relaxation
DEFF Research Database (Denmark)
Kjølby, Birgitte Fuglsang; Østergaard, Leif; Kiselev, Valerij G
2006-01-01
The concentration of MRI tracers cannot be measured directly by MRI and is commonly evaluated indirectly using their relaxation effect. This study develops a comprehensive theoretical model to describe the transverse relaxation in perfused tissue caused by intravascular tracers. The model takes...... into account a number of individual compartments. The signal dephasing is simulated in a semianalytical way by embedding Monte Carlo simulations in the framework of analytical theory. This approach yields a tool for fast, realistic simulation of the change in the transverse relaxation. The results indicate...... with bulk blood. The enhancement of relaxation in tissue is due to the contrast in magnetic susceptibility between blood vessels and parenchyma induced by the presence of paramagnetic tracer. Beyond the perfusion measurements, the results can be applied to quantitation of functional MRI and to vessel size...
LDRD final report on theory and exploration of quantum-dot optical nonlinearities and coherences
International Nuclear Information System (INIS)
Chow, Weng Wah
2008-01-01
A microscopic theory for investigating quantum-dot optical properties was developed. The theory incorporated advances on various aspects of quantum-dot physics developed at Sandia and elsewhere. Important components are a non-Markovian treatment of polarization dephasing due to carrier-carrier scattering (developed at Sandia) and a nonperturbative treatment within a polaron picture of the scattering of carriers by longitudinal-optical phonons (developed at Bremen University). A computer code was also developed that provides a detailed accounting of electronic structure influences and a consistent treatment of many-body effects, the latter via the incorporation of results from the microscopic theory. This code was used to explore quantum coherence physics in a quantum-dot system. The investigation furthers the understanding of the underlying differences between atomic quantum coherence and semiconductor quantum coherence, and helps improve the potential of using quantum coherences in quantum computing, coherent control and high-resolution spectroscopy
Energy Technology Data Exchange (ETDEWEB)
Kugler, Michael
2012-11-15
This work investigates the spin dynamics of holes in p-doped GaAs/AlGaAs quantum wells (QW) at low temperatures. To examine the energetic structure of the used samples, PL and PLE-spectroscopy were employed. Time resolved Kerr and Faraday-Rotation (TRKR/FR) and 'Resonant Spin Amplification' (RSA) were used to analyse the spin dynamics. First, the signal formation in TRKR/FR and RSA experiments is discussed taking into account the interconnected charge carrier dynamics and spin dynamics of electrons and holes. An excitation energy dependent sign change of the Kerr signal amplitude could be observed, whose energetic position corresponds to an absorption maximum in PLE experiments. This behavior could be explained by an energy dependent splitting of the spin niveaus, which leads to an energy dependence of the Faraday and Kerr signal. Furthermore, two initialization processes were investigated, which could be used to transfer optically generated spin information into the resident hole spin system. This could be achieved by either applying a magnetic field, or by rapid dephasing of hole spins immediately after excitation. Changes in excitation energy, excitation density or temperature could be used to influence the fast dephasing processes and therefore the initial ratio of hole to electron spins. The complex, interconnected charge carrier and spin dynamics of electrons and holes could be accurately reproduced using a rate equation model. This allowed for the extraction of physically relevant parameters like spin lifetimes and g-factors from RSA and TRKR/FR data. An analytical model that was developed at the Wroclaw University of Technology delivered matching results. In the second part of the experimental work, the dependence of the hole spin lifetime and the hole g-factor on various parameters was analysed. Here, the RSA method could for the first time be applied to two-dimensional hole systems, allowing for new insights into the regime of long lived hole
Fournier, Frédéric; Zheng, Wanquan; Carrez, Serge; Dubost, Henri; Bourguignon, Bernard
2004-09-01
Interaction of CO adsorbed on Pt(111) with electrons and phonons is studied experimentally by means of a pump-probe experiment where CO is probed by IR+visible sum frequency generation under a pump laser intensity that allows photodesorption. Vibrational spectra of CO internal stretch are obtained as a function of pump-probe delay. A two-temperature and anharmonic coupling model is used to extract from the spectra the real time variations of CO peak frequency and dephasing time. The main conclusions are the following: (i) The CO stretch is perturbed by two low-frequency modes, assigned to frustrated rotation and frustrated translation. (ii) The frustrated rotation is directly coupled to electrons photoexcited in Pt(111) by the pump laser. (iii) There is no evidence of Pt-CO stretch excitation in the spectra. The implications for the photodesorption dynamics are discussed.
A general circuit model for spintronic devices under electric and magnetic fields
Alawein, Meshal
2017-10-25
In this work, we present a circuit model of diffusive spintronic devices capable of capturing the effects of both electric and magnetic fields. Starting from a modified version of the well-established drift-diffusion equations, we derive general equivalent circuit models of semiconducting/metallic nonmagnets and metallic ferromagnets. In contrast to other models that are based on steady-state transport equations which might also neglect certain effects such as thermal fluctuations, spin dissipation in the ferromagnets, and spin precession under magnetic fields, our model incorporates most of the important physics and is based on a time-dependent formulation. An application of our model is shown through simulations of a nonlocal spin-valve under the presence of a magnetic field, where we reproduce experimental results of electrical measurements that demonstrate the phenomena of spin precession and dephasing (“Hanle effect”).
Magnetic resonance imaging of dystonic states
International Nuclear Information System (INIS)
Rutledge, J.N.; Hilal, S.K.; Silver, A.J.; Defendini, R.; Fahn, S.
1988-01-01
Interest in movement disorders is heightened by the recent capability of mapping the distribution of macromolecular complexes of Fe(III) in the brain using heavily T2-weighted images. This is accomplished through contrast caused by their T2 effect, a local inhomogeneity in the magnetic field which dephases spin and results in loss of signal. It is a unique characteristic of the extra-pyramidal system that its nuclei contain high concentrations of iron. The areas especially rich are the substantia nigra and globus pallidus. Lesser amounts of iron are found in the red nucleus, dentate nucleus, nigrostriatal tract, putamen, and caudate nucleus. The reasons for increased concentration of iron in nuclei related to movement are incompletely understood and are reviewed in this chapter
Features of statistical dynamics in a finite system
International Nuclear Information System (INIS)
Yan, Shiwei; Sakata, Fumihiko; Zhuo Yizhong
2002-01-01
We study features of statistical dynamics in a finite Hamilton system composed of a relevant one degree of freedom coupled to an irrelevant multidegree of freedom system through a weak interaction. Special attention is paid on how the statistical dynamics changes depending on the number of degrees of freedom in the irrelevant system. It is found that the macrolevel statistical aspects are strongly related to an appearance of the microlevel chaotic motion, and a dissipation of the relevant motion is realized passing through three distinct stages: dephasing, statistical relaxation, and equilibrium regimes. It is clarified that the dynamical description and the conventional transport approach provide us with almost the same macrolevel and microlevel mechanisms only for the system with a very large number of irrelevant degrees of freedom. It is also shown that the statistical relaxation in the finite system is an anomalous diffusion and the fluctuation effects have a finite correlation time
Physics at the FQMT'11 conference
International Nuclear Information System (INIS)
Špička, V; Nieuwenhuizen, Th M; Keefe, P D
2012-01-01
This paper deals with the recent state of the art of the following topics presented at the FQMT'11 conference: foundations of quantum physics, quantum measurement; nonequilibrium quantum statistical physics; quantum thermodynamics; quantum measurement, entanglement and coherence; dissipation, dephasing, noise, and decoherence; quantum optics; macroscopic quantum behavior; e.g. cold atoms; Bose-Einstein condensates; physics of quantum computing and quantum information; mesoscopic, nano-electro-mechanical systems and nano-optical systems; spin systems and their dynamics; biological systems and molecular motors; and cosmology, gravitation and astrophysics. The lectures and discussions at the FQMT'11 conference, as well as the contributions to the related topical issue, reveal important themes for future development. The recent literature is included.
DEFF Research Database (Denmark)
Borri, Paola; Langbein, Wolfgang; Mørk, Jesper
1999-01-01
We demonstrate a new detection scheme for pump-probe and four-wave mixing heterodyne experiments, using balanced detection and a dual-phase lock-in for spectral filtering. The technique allows the use of low repetition-rate laser systems, as is demonstrated on an InGaAsP/InP bulk optical amplifier...... at 1.53 mym. Ultrafast pump-induced changes in the amplitude and phase of the transmitted probe signal are simultaneously measured, going from small to large signal changes and with no need of an absolute phase calibration, showing the versatility and the sensitivity of this detection scheme....... The results for small perturbations are consistent with previous pump-probe experiments reported in literature. Time-resolved four-wave mixing in the absorption regime of the device is measured, and compared with numerical simulations, indicating a 100 fs dephasing time....
Robust quantum state engineering through coherent localization in biased-coin quantum walks
Energy Technology Data Exchange (ETDEWEB)
Majury, Helena [Queen' s University, Centre for Secure Information Technologies (CSIT), Belfast (United Kingdom); Queen' s University, Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Belfast (United Kingdom); Boutari, Joelle [University of Oxford, Clarendon Laboratory, Oxford (United Kingdom); O' Sullivan, Elizabeth [Queen' s University, Centre for Secure Information Technologies (CSIT), Belfast (United Kingdom); Ferraro, Alessandro; Paternostro, Mauro [Queen' s University, Centre for Theoretical Atomic, Molecular and Optical Physics, School of Mathematics and Physics, Belfast (United Kingdom)
2018-12-15
We address the performance of a coin-biased quantum walk as a generator for non-classical position states of the walker. We exploit a phenomenon of coherent localization in the position space - resulting from the choice of small values of the coin parameter and assisted by post-selection - to engineer large-size coherent superpositions of position states of the walker. The protocol that we design appears to be remarkably robust against both the actual value taken by the coin parameter and strong dephasing-like noise acting on the spatial degree of freedom. We finally illustrate a possible linear-optics implementation of our proposal, suitable for both bulk and integrated-optics platforms. (orig.)
Wein, Stephen; Lauk, Nikolai; Ghobadi, Roohollah; Simon, Christoph
2018-05-01
Highly efficient sources of indistinguishable single photons that can operate at room temperature would be very beneficial for many applications in quantum technology. We show that the implementation of such sources is a realistic goal using solid-state emitters and ultrasmall mode volume cavities. We derive and analyze an expression for photon indistinguishability that accounts for relevant detrimental effects, such as plasmon-induced quenching and pure dephasing. We then provide the general cavity and emitter conditions required to achieve efficient indistinguishable photon emission and also discuss constraints due to phonon sideband emission. Using these conditions, we propose that a nanodiamond negatively charged silicon-vacancy center combined with a plasmonic-Fabry-Pérot hybrid cavity is an excellent candidate system.
Noise and Fano-Factor Control in AC-Driven Aharonov-Casher Ring
Directory of Open Access Journals (Sweden)
Zein W. A.
2011-01-01
Full Text Available The spin dependent current and Fano factor of Aharonov-Casher semiconducting ring is investigated under the effect of microwave, infrared, ultraviolet radiation and magnetic field. Both the average current and the transport noise (Fano factor characteristics are expressed in terms of the tunneling probability for the respective scattering channels. For spin transport induced by microwave and infrared radiation, a random oscillatory behavior of the Fano factor is observed. These oscillations are due to constructive and destructive spin interference effects. While for the case of ultraviolet radiation, the Fano factor becomes constant. This is due to that the oscillations has been washed out by phase averaging (i.e. ensemble dephasing over the spin transport channels. The present investigation is very important for quantum computing and information processing.
Noise and Fano-factor Control in AC-Driven Aharonov-Casher Ring
Directory of Open Access Journals (Sweden)
Phillips A. H.
2011-01-01
Full Text Available The spin dependent current and Fano factor of Aharonov-Casher semiconducting ring is investigated under the effect of microwave, infrared, ultraviolet radiation and magnetic field. Both the average current and the transport noise (Fano factor characteristics are expressed in terms of the tunneling probability for the respective scattering channels. For spin transport induced by microwave and infrared radiation, a random oscillatory behavior of the Fano factor is observed. These oscillations are due to constructive and destructive spin interference effects. While for the case of ultraviolet radiation, the Fano factor becomes constant. This is due to that the oscillations has been washed out by phase averaging (i.e. ensemble dephasing over the spin transport channels. The present investigation is very important for quantum computing and information processing.
High-resolution flow imaging of the carotid arteries
International Nuclear Information System (INIS)
Masaryk, T.J.; Modic, M.T.; Haacke, E.M.; Lenz, G.W.; Ross, J.S.
1986-01-01
Recently, high-contrast vascular images have been demonstrated using short TEs, gating and subtraction. However, to obtain short TE values, large gradients are required. This potentially limits the field of view, signal-to-noise- ratio, and resolution. Furthermore, gating in different parts of the cardiac cycle can lead to pixel misregistration. In this study, additional refocusing gradients were applied so that no velocity-dependent dephasing occurs at the echo restoring signal from moving blood. Two cardiac-gated sequences using the same trigger delay and one acquisition were obtained. Preliminary results indicate that good quality vascular images of the carotid bifurcation can be obtained with modifications of the spin-echo technique of with short TEs utilizing a gradient echo technique
Decoherence by engineered quantum baths
Energy Technology Data Exchange (ETDEWEB)
Rossini, Davide [NEST-CNR-INFM and Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa (Italy); Calarco, Tommaso [Dipartimento di Fisica, Universita di Trento and BEC-CNR-INFM, I-38050 Povo (Italy); Giovannetti, Vittorio [NEST-CNR-INFM and Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa (Italy); Montangero, Simone [NEST-CNR-INFM and Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa (Italy); Fazio, Rosario [NEST-CNR-INFM and Scuola Normale Superiore, Piazza dei Cavalieri 7, I-56126 Pisa (Italy)
2007-07-13
Optical lattices can be used to simulate quantum baths and hence they can be of fundamental help to study, in a controlled way, the emergence of decoherence in quantum systems. Here we show how to implement a pure dephasing model for a two-level system coupled to an interacting spin bath. In this scheme it is possible to implement a large variety of spin environments embracing Ising, XY and Heisenberg universality classes. After having introduced the model, we calculate exactly the decoherence for the Ising and the XY spin bath model. We find universal features depending on the critical behaviour of the spin bath, both in the short- and long-time limits. The rich scenario that emerges can be tested experimentally and can be of importance for the understanding of the coherence loss in open quantum systems.
Energy Technology Data Exchange (ETDEWEB)
Maeda, Kiminori [Department of Chemistry, University of Oxford, Centre for Advanced Electron Spin Resonance, Inorganic Chemistry Laboratory, Oxford (United Kingdom); Liddell, Paul; Gust, Devens [Department of Chemistry and Biochemistry, Arizona State University, Tempe, Arizona, 85287-1604 (United States); Hore, P. J. [Department of Chemistry, University of Oxford, Physical and Theoretical Chemistry Laboratory, Oxford (United Kingdom)
2013-12-21
Spin-selective reactions of radical pairs are conventionally modelled using an approach that dates back to the 1970s [R. Haberkorn, Mol. Phys. 32, 1491 (1976)]. An alternative approach based on the theory of quantum measurements has recently been suggested [J. A. Jones and P. J. Hore, Chem. Phys. Lett. 488, 90 (2010)]. We present here the first experimental attempt to discriminate between the two models. Pulsed electron paramagnetic resonance spectroscopy has been used to investigate intramolecular electron transfer in the radical pair form of a carotenoid-porphyrin-fullerene molecular triad. The rate of spin-spin relaxation of the fullerene radical in the triad was found to be inconsistent with the quantum measurement description of the spin-selective kinetics, and in accord with the conventional model when combined with spin-dephasing caused by rotational modulation of the anisotropic g-tensor of the fullerene radical.
Interferometric probes of many-body localization.
Serbyn, M; Knap, M; Gopalakrishnan, S; Papić, Z; Yao, N Y; Laumann, C R; Abanin, D A; Lukin, M D; Demler, E A
2014-10-03
We propose a method for detecting many-body localization (MBL) in disordered spin systems. The method involves pulsed coherent spin manipulations that probe the dephasing of a given spin due to its entanglement with a set of distant spins. It allows one to distinguish the MBL phase from a noninteracting localized phase and a delocalized phase. In particular, we show that for a properly chosen pulse sequence the MBL phase exhibits a characteristic power-law decay reflecting its slow growth of entanglement. We find that this power-law decay is robust with respect to thermal and disorder averaging, provide numerical simulations supporting our results, and discuss possible experimental realizations in solid-state and cold-atom systems.
Concept for power scaling second harmonic generation using a cascade of nonlinear crystals
DEFF Research Database (Denmark)
Hansen, Anders Kragh; Tawfieq, Mahmoud; Jensen, Ole Bjarlin
2015-01-01
for efficient power scaling of single-pass SHG beyond such limits using a cascade of nonlinear crystals, in which the first crystal is chosen for high nonlinear efficiency and the subsequent crystal(s) are chosen for power handling ability. Using this highly efficient singlepass concept, we generate 3.7 W...... successfully combines the high efficiency of the first stage with the good power handling properties of the subsequent stages. The concept is generally applicable and can be expanded with more stages to obtain even higher efficiency, and extends also to other combinations of nonlinear media suitable for other......Within the field of high-power second harmonic generation (SHG), power scaling is often hindered by adverse crystal effects such as thermal dephasing arising from the second harmonic (SH) light, which imposes limits on the power that can be generated in many crystals. Here we demonstrate a concept...
Zhang, Xu; Chen, Ye-Hong; Wu, Qi-Cheng; Shi, Zhi-Cheng; Song, Jie; Xia, Yan
2017-01-01
We present an efficient scheme to quickly generate three-qubit Greenberger-Horne-Zeilinger (GHZ) states by using three superconducting qubits (SQs) separated by two coplanar waveguide resonators (CPWRs) capacitively. The scheme is based on quantum Zeno dynamics and the approach of transitionless quantum driving to construct shortcuts to adiabatic passage. In order to highlight the advantages, we compare the present scheme with the traditional one with adiabatic passage. The comparison result shows the shortcut scheme is closely related to the adiabatic scheme but is better than it. Moreover, we discuss the influence of various decoherences with numerical simulation. The result proves that the present scheme is less sensitive to the energy relaxation, the decay of CPWRs and the deviations of the experimental parameters the same as the adiabatic passage. However, the shortcut scheme is effective and robust against the dephasing of SQs in comparison with the adiabatic scheme.
International Nuclear Information System (INIS)
Daoud, M.; Ahl Laamara, R.
2012-01-01
We give the explicit expressions of the pairwise quantum correlations present in superpositions of multipartite coherent states. A special attention is devoted to the evaluation of the geometric quantum discord. The dynamics of quantum correlations under a dephasing channel is analyzed. A comparison of geometric measure of quantum discord with that of concurrence shows that quantum discord in multipartite coherent states is more resilient to dissipative environments than is quantum entanglement. To illustrate our results, we consider some special superpositions of Weyl–Heisenberg, SU(2) and SU(1,1) coherent states which interpolate between Werner and Greenberger–Horne–Zeilinger states. -- Highlights: ► Pairwise quantum correlations multipartite coherent states. ► Explicit expression of geometric quantum discord. ► Entanglement sudden death and quantum discord robustness. ► Generalized coherent states interpolating between Werner and Greenberger–Horne–Zeilinger states
Scalability of GHZ and random-state entanglement in the presence of decoherence
Energy Technology Data Exchange (ETDEWEB)
Melo, Fernando de; Tiersch, Markus; Buchleitner, Andreas [Physikalisches Institut, Albert-Ludwigs-Universitaet Freiburg (Germany); Aolita, Leandro; Cavalcanti, Daniel [ICFO - Institut de Ciencies Fotoniques (Spain); Acin, Antonio [ICFO - Institut de Ciencies Fotoniques (Spain); ICREA - Institucio Catalana de Recerca i Estudis Avancats (Spain); Salles, Alejo [Instituto de Fisica, Universidade Federal do Rio de Janeiro (Brazil); Physikalisches Institut, Albert-Ludwigs-Universitaet Freiburg (Germany)
2009-07-01
We derive analytical upper bounds for the entanglement of generalized Greenberger-Horne-Zeilinger (GHZ) states locally coupled to dephasing, depolarizing, and thermal reservoirs. The derivation is carried out under very weak constraints, and holds for any convex quantifier of entanglement. The obtained bounds reveal an exponential entanglement decay with the number of qubits - the robustness of the generalized GHZ states decreases exponentially with the system size. This poses a severe limitation to many quantum communication protocols. A comparison between the entanglement decay of randomly generated states with the GHZ family shows that the former decays slower, thus violating the previously obtained bounds. Furthermore, the random state's entanglement is more robust against noise for larger system size.
Perspectives for quantum interference with biomolecules and biomolecular clusters
International Nuclear Information System (INIS)
Geyer, P; Sezer, U; Rodewald, J; Mairhofer, L; Dörre, N; Haslinger, P; Eibenberger, S; Brand, C; Arndt, M
2016-01-01
Modern quantum optics encompasses a wide field of phenomena that are either related to the discrete quantum nature of light, the quantum wave nature of matter or light–matter interactions. We here discuss new perspectives for quantum optics with biological nanoparticles. We focus in particular on the prospects of matter-wave interferometry with amino acids, nucleotides, polypeptides or DNA strands. We motivate the challenge of preparing these objects in a ‘biomimetic’ environment and argue that hydrated molecular beam sources are promising tools for quantum-assisted metrology. The method exploits the high sensitivity of matter-wave interference fringes to dephasing and shifts in the presence of external perturbations to access and determine molecular properties. (invited comment)
Energy Technology Data Exchange (ETDEWEB)
Daoud, M., E-mail: m_daoud@hotmail.com [Department of Physics, Faculty of Sciences, University Ibnou Zohr, Agadir (Morocco); Ahl Laamara, R., E-mail: ahllaamara@gmail.com [LPHE-Modeling and Simulation, Faculty of Sciences, University Mohammed V, Rabat (Morocco); Centre of Physics and Mathematics, CPM, CNESTEN, Rabat (Morocco)
2012-07-16
We give the explicit expressions of the pairwise quantum correlations present in superpositions of multipartite coherent states. A special attention is devoted to the evaluation of the geometric quantum discord. The dynamics of quantum correlations under a dephasing channel is analyzed. A comparison of geometric measure of quantum discord with that of concurrence shows that quantum discord in multipartite coherent states is more resilient to dissipative environments than is quantum entanglement. To illustrate our results, we consider some special superpositions of Weyl–Heisenberg, SU(2) and SU(1,1) coherent states which interpolate between Werner and Greenberger–Horne–Zeilinger states. -- Highlights: ► Pairwise quantum correlations multipartite coherent states. ► Explicit expression of geometric quantum discord. ► Entanglement sudden death and quantum discord robustness. ► Generalized coherent states interpolating between Werner and Greenberger–Horne–Zeilinger states.
Decoherence in the Kane quantum computer
International Nuclear Information System (INIS)
Fowler, A.G.; Wellard, C.J.; Hollenberg, L.C.L.
2002-01-01
Full text: The Kane design for a quantum computer in the solid-state has recently received a great deal of attention, and is the main area of study in the Special Research Centre for Quantum Computer Technology. In this paper, the adiabatic CNOT gate, as proposed by Goan and Milburn, is simulated exactly for a range of pulse sequence profiles. In the absence of de-phasing, the CNOT gate operation time (semi-optimized) was found to be 26 micro-seconds with error probability of 5 x 10 -5 . Simulation of the CNOT gate in the presence of a coherence destroying environmental coupling as well as gate noise was subsequently carried out for a range of de-coherence rates, and the effect on gate fidelity determined
Majd, Nayereh; Ghasemi, Zahra
2016-10-01
We have investigated a TPTQ state as an input state of a non-ideal ferromagnetic detectors. Minimal spin polarization required to demonstrate spin entanglement according to entanglement witness and CHSH inequality with respect to (w.r.t.) their two free parameters have been found, and we have numerically shown that the entanglement witness is less stringent than the direct tests of Bell's inequality in the form of CHSH in the entangled limits of its free parameters. In addition, the lower limits of spin detection efficiency fulfilling secure cryptographic key against eavesdropping have been derived. Finally, we have considered TPTQ state as an output of spin decoherence channel and the region of ballistic transmission time w.r.t. spin relaxation time and spin dephasing time has been found.
Double-sided coaxial circuit QED with out-of-plane wiring
Rahamim, J.; Behrle, T.; Peterer, M. J.; Patterson, A.; Spring, P. A.; Tsunoda, T.; Manenti, R.; Tancredi, G.; Leek, P. J.
2017-05-01
Superconducting circuits are well established as a strong candidate platform for the development of quantum computing. In order to advance to a practically useful level, architectures are needed which combine arrays of many qubits with selective qubit control and readout, without compromising on coherence. Here, we present a coaxial circuit quantum electrodynamics architecture in which qubit and resonator are fabricated on opposing sides of a single chip, and control and readout wiring are provided by coaxial wiring running perpendicular to the chip plane. We present characterization measurements of a fabricated device in good agreement with simulated parameters and demonstrating energy relaxation and dephasing times of T1 = 4.1 μs and T2 = 5.7 μs, respectively. The architecture allows for scaling to large arrays of selectively controlled and measured qubits with the advantage of all wiring being out of the plane.
Long-lived periodic revivals of coherence in an interacting Bose-Einstein condensate
Energy Technology Data Exchange (ETDEWEB)
Egorov, M.; Ivannikov, V.; Opanchuk, B.; Drummond, P.; Hall, B. V.; Sidorov, A. I. [ARC Centre of Excellence for Quantum-Atom Optics and Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne 3122 (Australia); Anderson, R. P. [ARC Centre of Excellence for Quantum-Atom Optics and Centre for Atom Optics and Ultrafast Spectroscopy, Swinburne University of Technology, Melbourne 3122 (Australia); School of Physics, Monash University, Victoria 3800 (Australia)
2011-08-15
We observe the coherence of an interacting two-component Bose-Einstein condensate (BEC) surviving for seconds in a trapped Ramsey interferometer. Mean-field-driven collective oscillations of two components lead to periodic dephasing and rephasing of condensate wave functions with a slow decay of the interference fringe visibility. We apply spin echo synchronous with the self-rephasing of the condensate to reduce the influence of state-dependent atom losses, significantly enhancing the visibility up to 0.75 at the evolution time of 1.5 s. Mean-field theory consistently predicts higher visibility than experimentally observed values. We quantify the effects of classical and quantum noise and infer a coherence time of 2.8 s for a trapped condensate of 5.5x10{sup 4} interacting atoms.
Single-Photon Nonlinear Optics in Integrated Hollow-Core Waveguides
2010-10-13
IM_,io{f I +1-o (q&r H-a.w kh<->1 A:a.ro •L- "£. Lll!.L , ’J3 i_""- th.d iJerr 1 Jo lu1. F I UC t)i;t•- vlc - Cntc- 1 /’S’~ His k S-f . Sa.ccfa...this has proven to be challenging as the rubidium is very reactive with air. Attaching a reservoir using anodic bonding techniques is hard to...exciting prospect. 7.2 Remaining challenges The dephasing rate can be even lowered in our device by reducing the experimental 190
Acoustically induced spin transport in (110)GaAs quantum wells
Energy Technology Data Exchange (ETDEWEB)
Couto, Odilon D.D. Jr.
2008-09-29
In this work, we employ surface acoustic waves (SAWs) to transport and manipulate optically generated spin ensembles in (110) GaAs quantum wells (QWs). The strong carrier confinement into the SAW piezoelectric potential allows for the transport of spin-polarized carrier packets along well-defined channels with the propagation velocity of the acoustic wave. In this way, spin transport over distances exceeding 60 m is achieved, corresponding to spin lifetimes longer than 20 ns. The demonstration of such extremely long spin lifetimes is enabled by three main factors: (i) Suppression of the D'yakonov-Perel' spin relaxation mechanism for z-oriented spins in (110) IIIV QWs; (ii) Suppression of the Bir-Aronov-Pikus spin relaxation mechanism caused by the type-II SAW piezoelectric potential; (iii) Suppression of spin relaxation induced by the mesoscopic carrier confinement into narrow stripes along the SAW wave front direction. A spin transport anisotropy under external magnetic fields (B{sub ext}) is demonstrated for the first time. Employing the well-defined average carrier momentum impinged by the SAW, we analyze the spin dephasing dynamics during transport along the [001] and [1 anti 10] in-plane directions. For transport along [001], fluctuations of the internal magnetic field (B{sub int}), which arises from the spin-orbit interaction associated with the bulk inversion asymmetry of the crystal, lead to decoherence within 2 ns as the spins precess around B{sub ext}. In contrast, for transport along the [1 anti 10] direction, the z-component of the spin polarization is maintained for times one order of magnitude longer due to the non-zero average value of B{sub int}. The dephasing anisotropy between the two directions is fully understood in terms of the dependence of the spin-orbit coupling on carrier momentum direction, as predicted by the D'yakonov-Perel' mechanism for the (110) system. (orig.)
CdZnTe quantum dots study: energy and phase relaxation process
International Nuclear Information System (INIS)
Viale, Yannick
2004-01-01
We present a study of the electron-hole pair energy and phase relaxation processes in a CdTe/ZnTe heterostructure, in which quantum dots are embedded. CdZnTe quantum wells with a high Zinc concentration, separated by ZnTe barriers, contain islands with a high cadmium concentration. In photoluminescence excitation spectroscopy experiments, we evidence two types of electron hole pair relaxation processes. After being excited in the CdZnTe quantum well, the pairs relax their energy by emitting a cascade of longitudinal optical phonons until they are trapped in the quantum dots. Before their radiative recombination follows an intra-dot relaxation, which is attributed to a lattice polarization mechanism of the quantum dots. It is related to the coupling between the electronic and the vibrational states. Both relaxation mechanisms are reinforced by the strong polar character of the chemical bond in II-VI compounds. Time resolved measurements of transmission variations in a pump-probe configuration allowed us to investigate the population dynamics of the electron-hole pairs during the relaxation process. We observe a relaxation time of about 2 ps for the longitudinal phonon emission cascade in the quantum well before a saturation of the quantum dot transition. We also measured an intra-box relaxation time of 25 ps. The comparison of various cascades allows us to estimate the emission time of a longitudinal optical phonon in the quantum well to be about 100 fs. In four waves mixing experiments, we observe oscillations that we attribute to quantum beats between excitonic and bi-excitonic transitions. The dephasing times that we measure as function of the density of photons shows that excitons are strongly localized in the quantum dots. The excitonic dephasing time is much shorter than the radiative lifetime and is thus controlled by the intra-dot relaxation time. (author) [fr
Excitonic energy transfer in light-harvesting complexes in purple bacteria
International Nuclear Information System (INIS)
Ye Jun; Sun Kewei; Zhao Yang; Lee, Chee Kong; Yu Yunjin; Cao Jianshu
2012-01-01
Two distinct approaches, the Frenkel-Dirac time-dependent variation and the Haken-Strobl model, are adopted to study energy transfer dynamics in single-ring and double-ring light-harvesting (LH) systems in purple bacteria. It is found that the inclusion of long-range dipolar interactions in the two methods results in significant increase in intra- or inter-ring exciton transfer efficiency. The dependence of exciton transfer efficiency on trapping positions on single rings of LH2 (B850) and LH1 is similar to that in toy models with nearest-neighbor coupling only. However, owing to the symmetry breaking caused by the dimerization of BChls and dipolar couplings, such dependence has been largely suppressed. In the studies of coupled-ring systems, both methods reveal an interesting role of dipolar interactions in increasing energy transfer efficiency by introducing multiple intra/inter-ring transfer paths. Importantly, the time scale (4 ps) of inter-ring exciton transfer obtained from polaron dynamics is in good agreement with previous studies. In a double-ring LH2 system, non-nearest neighbor interactions can induce symmetry breaking, which leads to global and local minima of the average trapping time in the presence of a non-zero dephasing rate, suggesting that environment dephasing helps preserve quantum coherent energy transfer when the perfect circular symmetry in the hypothetic system is broken. This study reveals that dipolar coupling between chromophores may play an important role in the high energy transfer efficiency in the LH systems of purple bacteria and many other natural photosynthetic systems.
Excitonic energy transfer in light-harvesting complexes in purple bacteria
Energy Technology Data Exchange (ETDEWEB)
Ye Jun; Sun Kewei; Zhao Yang; Lee, Chee Kong [School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore); Yu Yunjin [School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798 (Singapore); College of Physics Science and Technology, Shenzhen University, Guangdong 518060 (China); Cao Jianshu [Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
2012-06-28
Two distinct approaches, the Frenkel-Dirac time-dependent variation and the Haken-Strobl model, are adopted to study energy transfer dynamics in single-ring and double-ring light-harvesting (LH) systems in purple bacteria. It is found that the inclusion of long-range dipolar interactions in the two methods results in significant increase in intra- or inter-ring exciton transfer efficiency. The dependence of exciton transfer efficiency on trapping positions on single rings of LH2 (B850) and LH1 is similar to that in toy models with nearest-neighbor coupling only. However, owing to the symmetry breaking caused by the dimerization of BChls and dipolar couplings, such dependence has been largely suppressed. In the studies of coupled-ring systems, both methods reveal an interesting role of dipolar interactions in increasing energy transfer efficiency by introducing multiple intra/inter-ring transfer paths. Importantly, the time scale (4 ps) of inter-ring exciton transfer obtained from polaron dynamics is in good agreement with previous studies. In a double-ring LH2 system, non-nearest neighbor interactions can induce symmetry breaking, which leads to global and local minima of the average trapping time in the presence of a non-zero dephasing rate, suggesting that environment dephasing helps preserve quantum coherent energy transfer when the perfect circular symmetry in the hypothetic system is broken. This study reveals that dipolar coupling between chromophores may play an important role in the high energy transfer efficiency in the LH systems of purple bacteria and many other natural photosynthetic systems.
Interpreting quantum coherence through a quantum measurement process
Yao, Yao; Dong, G. H.; Xiao, Xing; Li, Mo; Sun, C. P.
2017-11-01
Recently, there has been a renewed interest in the quantification of coherence or other coherencelike concepts within the framework of quantum resource theory. However, rigorously defined or not, the notion of coherence or decoherence has already been used by the community for decades since the advent of quantum theory. Intuitively, the definitions of coherence and decoherence should be two sides of the same coin. Therefore, a natural question is raised: How can the conventional decoherence processes, such as the von Neumann-Lüders (projective) measurement postulation or partially dephasing channels, fit into the bigger picture of the recently established theoretical framework? Here we show that the state collapse rules of the von Neumann or Lüders-type measurements, as special cases of genuinely incoherent operations (GIOs), are consistent with the resource theories of quantum coherence. New hierarchical measures of coherence are proposed for the Lüders-type measurement and their relationship with measurement-dependent discord is addressed. Moreover, utilizing the fixed-point theory for C* algebra, we prove that GIOs indeed represent a particular type of partially dephasing (phase-damping) channels which have a matrix representation based on the Schur product. By virtue of the Stinespring dilation theorem, the physical realizations of incoherent operations are investigated in detail and we find that GIOs in fact constitute the core of strictly incoherent operations and generally incoherent operations and the unspeakable notion of coherence induced by GIOs can be transferred to the theories of speakable coherence by the corresponding permutation or relabeling operators.
Cao, X.; Mastalerz, Maria; Chappell, M.A.; Miller, L.F.; Li, Y.; Mao, J.
2011-01-01
Four lithotypes (vitrain, bright clarain, clarain, and fusain) of a high volatile bituminous Springfield Coal from the Illinois Basin were characterized using advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. The NMR techniques included quantitative direct polarization/magic angle spinning (DP/MAS), cross polarization/total sideband suppression (CP/TOSS), dipolar dephasing, CHn selection, and recoupled C-H long-range dipolar dephasing techniques. The lithotypes that experienced high-pressure CO2 adsorption isotherm analysis were also analyzed to determine possible changes in coal structure as a result of CO2 saturation at high pressure and subsequent evacuation. The main carbon functionalities present in original vitrain, bright clarain, clarain and fusain were aromatic carbons (65.9%-86.1%), nonpolar alkyl groups (9.0%-28.9%), and aromatic C-O carbons (4.1%-9.5%). Among these lithotypes, aromaticity increased in the order of clarain, bright clarain, vitrain, and fusain, whereas the fraction of alkyl carbons decreased in the same order. Fusain was distinct from other three lithotypes in respect to its highest aromatic composition (86.1%) and remarkably small fraction of alkyl carbons (11.0%). The aromatic cluster size in fusain was larger than that in bright clarain. The lithotypes studied responded differently to high pressure CO2 saturation. After exposure to high pressure CO2, vitrain and fusain showed a decrease in aromaticity but an increase in the fraction of alkyl carbons, whereas bright clarain and clarain displayed an increase in aromaticity but a decrease in the fraction of alkyl carbons. Aromatic fused-rings were larger for bright clarain but smaller for fusain in the post-CO2 adsorption samples compared to the original lithotypes. These observations suggested chemical CO2-coal interactions at high pressure and the selectivity of lithotypes in response to CO2 adsorption. ?? 2011 Elsevier B.V.
Quantum correlations of coupled superconducting two-qubit system in various cavity environments
International Nuclear Information System (INIS)
Yu, Yanxia; Fu, Guolan; Guo, L.P.; Pan, Hui; Wang, Z.S.
2013-01-01
Highlights: •We investigate dynamic evolutions of quantum and classical correlations for coupled superconducting system with various cavity environments. •We show that the quantum discord continues to reflect quantum information. •A transition of quantum discord is founded between classical loss and quantum increasing of correlations for a purely dephasing mode. •We show that the environment-dependent models can delay the loss of quantum discord. •We find that the results depend strongly on the initial angle. -- Abstract: Dynamic evolutions of quantum discord, concurrence, and classical correlation are investigated in coupled superconducting system with various cavity environments, focusing on the two-qubit system at an initially entangling X-state and Y-state. We find that for a smaller photon number, the quantum discord, concurrence and classical correlation show damped oscillations for all different decay modes. Differently from the sudden death or the dark and bright periods emerging in evolving processing of the concurrence and classical correlation, however, the quantum discord decreases gradually to zero. The results reveal that the quantum entanglement and classical correlation are lost, but the quantum discord continues to reflect quantum information in the same evolving period. For a larger photon number, the oscillations disappear. It is surprised that there exists a transition of quantum discord between classical loss and quantum increasing of correlations for a purely dephasing mode. For a larger photon number in the Y-state, the transition disappears. Moreover, we show that the environment-dependent models can delay the loss of quantum discord. The results depend strongly on the initial angle, which provide a clue to control the quantum gate of superconducting circuit
Spin-locking of half-integer quadrupolar nuclei in NMR of solids: The far off-resonance case.
Odedra, Smita; Wimperis, Stephen
Spin-locking of spin I=3/2 and I=5/2 nuclei in the presence of large resonance offsets has been studied using both approximate and exact theoretical approaches and, in the case of I=3/2, experimentally. We show the variety of coherences and population states produced in a far off-resonance spin-locking NMR experiment (one consisting solely of a spin-locking pulse) and how these vary with the radiofrequency field strength and offset frequency. Under magic angle spinning (MAS) conditions and in the "adiabatic limit", these spin-locked states acquire a time dependence. We discuss the rotor-driven interconversion of the spin-locked states, using an exact density matrix approach to confirm the results of the approximate model. Using conventional and multiple-quantum filtered spin-locking 23 Na (I=3/2) NMR experiments under both static and MAS conditions, we confirm the results of the theoretical calculations, demonstrating the applicability of the approximate theoretical model to the far off-resonance case. This simplified model includes only the effects of the initial rapid dephasing of coherences that occurs at the start of the spin-locking period and its success in reproducing both experimental and exact simulation data indicates that it is this dephasing that is the dominant phenomenon in NMR spin-locking of quadrupolar nuclei, as we have previously found for the on-resonance and near-resonance cases. Potentially, far off-resonance spin-locking of quadrupolar nuclei could be of interest in experiments such as cross polarisation as a consequence of the spin-locking pulse being applied to a better defined initial state (the thermal equilibrium bulk magnetisation aligned along the z-axis) than can be created in a powdered solid with a selective radiofrequency pulse, where the effect of the pulse depends on the orientation of the individual crystallites. Copyright © 2016 Elsevier Inc. All rights reserved.
Stacking of purines in water: the role of dipolar interactions in caffeine.
Tavagnacco, L; Di Fonzo, S; D'Amico, F; Masciovecchio, C; Brady, J W; Cesàro, A
2016-05-11
During the last few decades it has been ascertained that base stacking is one of the major contributions stabilizing nucleic acid conformations. However, the understanding of the nature of the interactions involved in the stacking process remains under debate and it is a subject of theoretical and experimental studies. Structural similarity between purine bases (guanine and adenine) in DNA and the caffeine molecule makes caffeine an excellent model for the purine bases. The present study clearly shows that dipolar interactions play a fundamental role in determining stacking of purine molecules in solution. In order to reach this achievement, polarized ultraviolet Raman resonant scattering experiments have been carried out on caffeine aqueous solutions as a function of concentration and temperature. The investigation pointed out at the aggregation and solvation properties, particularly at elevated temperatures. Kubo-Anderson theory was used as a framework to investigate the non-coincidence effect (NCE) occurring in the totally symmetric breathing modes of the purine rings, and in the bending modes of the methyl groups of caffeine. The NCE concentration dependence shows that caffeine aggregation at 80 °C occurs by planar stacking of the hydrophobic faces. The data clearly indicate that dipolar interactions determine the reorientational motion of the molecules in solution and are the driving force for the stacking of caffeine. In parallel, the observed dephasing times imply a change in caffeine interactions as a function of temperature and concentration. A decrease, at low water content, of the dephasing time for the ring breathing vibration mode indicates that self-association alters the solvation structure that is detectable at low concentration. These results are in agreement with simulation predictions and serve as an important validation of the models used in those calculations.
The interplay of superconducting quantum circuits and propagating microwave states
Energy Technology Data Exchange (ETDEWEB)
Goetz, Jan
2017-06-26
Superconducting circuit quantum electrodynamics (QED) has developed into a powerful platform for studying the interaction between matter and different states of light. In this context, superconducting quantum bits (qubits) act as artificial atoms interacting with quantized modes of the electromagnetic field. The field can be trapped in superconducting microwave resonators or propagating in transmission lines. In this thesis, we particularly study circuit QED systems where microwave fields are coupled with superconducting flux and transmon qubits. We optimize the coherence properties of the resonators, by analyzing loss mechanisms at excitation powers of approximately one photon on average. We find that two-level fluctuators associated with oxide layers at substrate and metal surfaces and metal-metal interfaces represent the predominant loss channel. Furthermore, we show how broadband thermal photon fields influence the relaxation and dephasing properties of a superconducting transmon qubit. To this end, we study several second-order loss channels of the transmon qubit and find that the broadband fields introduce a larger decay rate than expected from the Purcell filter defined by the resonator. Additionally, we show that qubit dephasing at the flux-insensitive point as well as low-frequency parameter fluctuations can be enhanced by thermal fields. Finally, we study how artificial atoms react to changes in inherent properties of the light fields. We perform a detailed analysis of the photon statistics of thermal fields using their relation to the qubits coherence properties. We quantitatively recover the expected n{sup 2} + n-law for the photon number variance and confirm this result by direct correlation measurements. We then show a novel technique for the in-situ conversion of the interaction parity in light-matter interaction. To this end, we couple spatially controlled microwave fields to a flux qubit with two degrees of freedom.
LLE 1997. Annual report, October 1996-September 1997
International Nuclear Information System (INIS)
1998-01-01
The fiscal year ending September 1997 (FY97) concluded the fifth year of the cooperative agreement (DE-FC03-92SF19460) with the U.S. Department of Energy (DOE). This report summarizes research at the Laboratory for Laser Energetics (LLE) and is the final report for the first five years of the cooperative agreement. In September 1997, the cooperative agreement was renewed for an additional five years. We summarize our research during FY97, the operation of the National Laser Users' Facility (NLUF), and the education of high school, undergraduate, and graduate students in LLE programs. A general introduction to LLE's experimental physics program and a report on recent results are found on pp. 161-167. This article includes a useful summary of the system's operational capabilities and system parameters after three years of operation. Direct-drive inertial confinement fusion requires precise drive uniformity, the control of hydrodynamic instabilities during the implosion of the fusion target, and accurate target fabrication and characterization. The article summarizes a wide variety of experiments relating to direct-drive laser fusion, from high-yield implosion experiments to planar and spherical Rayleigh-Taylor experiments, laser-imprinting experiments, and laser-plasma interaction experiments. A detailed analysis of the equation of motion for an electron in a plane wave is presented beginning on p. 24. A guiding center model is postulated and compared to numerical simulation of the actual particle motion. The formula is also verified analytically using the method of multiple scales. Work continues on this formalism to study the effects of the pondermotive force on laser-plasma interactions. A theoretical calculation of the dephasing time of an electron accelerated by a laser pulse is found on pp. 92-100. The trajectory of a charged particle, determined analytically for various pulse shapes, is then used to determine the dephasing time of an accelerated particle
Testing effective quantum gravity with gravitational waves from extreme mass ratio inspirals
International Nuclear Information System (INIS)
Yunes, N; Sopuerta, C F
2010-01-01
Testing deviation of GR is one of the main goals of the proposed Laser Interferometer Space Antenna. For the first time, we consistently compute the generation of gravitational waves from extreme-mass ratio inspirals (stellar compact objects into supermassive black holes) in a well-motivated alternative theory of gravity, that to date remains weakly constrained by double binary pulsar observations. The theory we concentrate on is Chern-Simons (CS) modified gravity, a 4-D, effective theory that is motivated both from string theory and loop-quantum gravity, and which enhances the Einstein-Hilbert action through the addition of a dynamical scalar field and the parity-violating Pontryagin density. We show that although point particles continue to follow geodesics in the modified theory, the background about which they inspiral is a modification to the Kerr metric, which imprints a CS correction on the gravitational waves emitted. CS modified gravitational waves are sufficiently different from the General Relativistic expectation that they lead to significant dephasing after 3 weeks of evolution, but such dephasing will probably not prevent detection of these signals, but instead lead to a systematic error in the determination of parameters. We end with a study of radiation-reaction in the modified theory and show that, to leading-order, energy-momentum emission is not CS modified, except possibly for the subdominant effect of scalar-field emission. The inclusion of radiation-reaction will allow for tests of CS modified gravity with space-borne detectors that might be two orders of magnitude larger than current binary pulsar bounds.
Optical logic gates based on electro-optic modulation with Sagnac interferometer.
Li, Qiliang; Zhu, Mengyun; Li, Dongqiang; Zhang, Zhen; Wei, Yizhen; Hu, Miao; Zhou, Xuefang; Tang, Xianghong
2014-07-20
In this work, we present a new structure to realize optical logic operation in a Sagnac interferometer with electro-optical modulation. In the scheme, we divide two counterpropagation signals in a Sagnac loop to two different arms with the electro-optical crystal by using two circulators. Lithium niobate materials whose electro-optical coefficient can be as large as 32.2×10(-12) m/V make up the arms of the waveguides. Using the transfer matrix of the fiber coupler, we analyze the propagation of signals in this system and obtain the transmission characteristic curves and the extinction ratio. The results indicate that this optical switching has a high extinction ratio of about 60 dB and an ultrafast response time of 2.036 ns. In addition, the results reveal that the change of the dephasing between the two input signals and the modification of the modulation voltage added to the electro-optical crystal leads to the change of the extinction ratio. We also conclude that, in cases of the dephasing of two initial input signals Δφ=0, we can obtain the various logical operations, such as the logical operations D=A¯·B, D=A·B¯, C=A+B, and D=A⊕B in ports C and D of the system by adjusting the modulation voltage. When Δφ≠0, we obtain the arithmetic operations D=A+B, C=A⊕B, D=A·B¯, and C=A¯·B in ports C and D. This study is significant for the design of all optical networks by adjusting the modulation voltage.
LLE 1997. Annual report, October 1996--September 1997
Energy Technology Data Exchange (ETDEWEB)
NONE
1998-01-01
The fiscal year ending September 1997 (FY97) concluded the fifth year of the cooperative agreement (DE-FC03-92SF19460) with the U.S. Department of Energy (DOE). This report summarizes research at the Laboratory for Laser Energetics (LLE) and is the final report for the first five years of the cooperative agreement. In September 1997, the cooperative agreement was renewed for an additional five years. We summarize our research during FY97, the operation of the National Laser Users` Facility (NLUF), and the education of high school, undergraduate, and graduate students in LLE programs. A general introduction to LLE`s experimental physics program and a report on recent results are found on pp. 161-167. This article includes a useful summary of the system`s operational capabilities and system parameters after three years of operation. Direct-drive inertial confinement fusion requires precise drive uniformity, the control of hydrodynamic instabilities during the implosion of the fusion target, and accurate target fabrication and characterization. The article summarizes a wide variety of experiments relating to direct-drive laser fusion, from high-yield implosion experiments to planar and spherical Rayleigh-Taylor experiments, laser-imprinting experiments, and laser-plasma interaction experiments. A detailed analysis of the equation of motion for an electron in a plane wave is presented beginning on p. 24. A guiding center model is postulated and compared to numerical simulation of the actual particle motion. The formula is also verified analytically using the method of multiple scales. Work continues on this formalism to study the effects of the pondermotive force on laser-plasma interactions. A theoretical calculation of the dephasing time of an electron accelerated by a laser pulse is found on pp. 92-100. The trajectory of a charged particle, determined analytically for various pulse shapes, is then used to determine the dephasing time of an accelerated particle.
The interplay of superconducting quantum circuits and propagating microwave states
International Nuclear Information System (INIS)
Goetz, Jan
2017-01-01
Superconducting circuit quantum electrodynamics (QED) has developed into a powerful platform for studying the interaction between matter and different states of light. In this context, superconducting quantum bits (qubits) act as artificial atoms interacting with quantized modes of the electromagnetic field. The field can be trapped in superconducting microwave resonators or propagating in transmission lines. In this thesis, we particularly study circuit QED systems where microwave fields are coupled with superconducting flux and transmon qubits. We optimize the coherence properties of the resonators, by analyzing loss mechanisms at excitation powers of approximately one photon on average. We find that two-level fluctuators associated with oxide layers at substrate and metal surfaces and metal-metal interfaces represent the predominant loss channel. Furthermore, we show how broadband thermal photon fields influence the relaxation and dephasing properties of a superconducting transmon qubit. To this end, we study several second-order loss channels of the transmon qubit and find that the broadband fields introduce a larger decay rate than expected from the Purcell filter defined by the resonator. Additionally, we show that qubit dephasing at the flux-insensitive point as well as low-frequency parameter fluctuations can be enhanced by thermal fields. Finally, we study how artificial atoms react to changes in inherent properties of the light fields. We perform a detailed analysis of the photon statistics of thermal fields using their relation to the qubits coherence properties. We quantitatively recover the expected n 2 + n-law for the photon number variance and confirm this result by direct correlation measurements. We then show a novel technique for the in-situ conversion of the interaction parity in light-matter interaction. To this end, we couple spatially controlled microwave fields to a flux qubit with two degrees of freedom.
Zhang, Baixiong; Tan, Junjun; Li, Chuanzhao; Zhang, Jiahui; Ye, Shuji
2018-06-13
The balance of lipid-peptide and peptide-peptide interactions at cell membrane is essential to a large variety of cellular processes. In this study, we have experimentally demonstrated for the first time that sum frequency generation vibrational spectroscopy can be used to probe the peptide-peptide and lipid-peptide interactions in cell membrane in situ and in real time by determination of the line width of amide I band of protein backbone. Using a "benchmark" model of α-helical WALP23, it is found that the dominated lipid-peptide interaction causes a narrow line width of the amide I band, whereas the peptide-peptide interaction can markedly broaden the line width. When WALP23 molecules insert into the lipid bilayer, a quite narrow line width of the amide I band is observed because of the lipid-peptide interaction. In contrast, when the peptide lies down on the bilayer surface, the line width of amide I band becomes very broad owing to the peptide-peptide interaction. In terms of the real-time change in the line width, the transition from peptide-peptide interaction to lipid-peptide interaction is monitored during the insertion of WALP23 into 1,2-dipalmitoyl- sn-glycero-3-phospho-(1'- rac-glycerol) (DPPG) lipid bilayer. The dephasing time of a pure α-helical WALP23 in 1-palmitoyl-2-oleoyl- sn-glycero-3-phospho-(1'- rac-glycerol) and DPPG bilayer is determined to be 2.2 and 0.64 ps, respectively. The peptide-peptide interaction can largely accelerate the dephasing time.
Cao, Xiaoyan; Birdwell, Justin E.; Chappell, Mark A.; Li, Yuan; Pignatello, Joseph J.; Mao, Jingdong
2013-01-01
Characterization of oil shale kerogen and organic residues remaining in postpyrolysis spent shale is critical to the understanding of the oil generation process and approaches to dealing with issues related to spent shale. The chemical structure of organic matter in raw oil shale and spent shale samples was examined in this study using advanced solid-state 13C nuclear magnetic resonance (NMR) spectroscopy. Oil shale was collected from Mahogany zone outcrops in the Piceance Basin. Five samples were analyzed: (1) raw oil shale, (2) isolated kerogen, (3) oil shale extracted with chloroform, (4) oil shale retorted in an open system at 500°C to mimic surface retorting, and (5) oil shale retorted in a closed system at 360°C to simulate in-situ retorting. The NMR methods applied included quantitative direct polarization with magic-angle spinning at 13 kHz, cross polarization with total sideband suppression, dipolar dephasing, CHn selection, 13C chemical shift anisotropy filtering, and 1H-13C long-range recoupled dipolar dephasing. The NMR results showed that, relative to the raw oil shale, (1) bitumen extraction and kerogen isolation by demineralization removed some oxygen-containing and alkyl moieties; (2) unpyrolyzed samples had low aromatic condensation; (3) oil shale pyrolysis removed aliphatic moieties, leaving behind residues enriched in aromatic carbon; and (4) oil shale retorted in an open system at 500°C contained larger aromatic clusters and more protonated aromatic moieties than oil shale retorted in a closed system at 360°C, which contained more total aromatic carbon with a wide range of cluster sizes.
Frank, Milan; Jelínek, Michal; Kubeček, Václav; Ivleva, Lyudmila I.; Zverev, Petr G.; Smetanin, Sergei
2017-12-01
A lot of attention is currently focused on synchronously pumped, extra-cavity crystalline Raman lasers generating one or two Stokes Raman components in KGW or diamond Raman-active crystals, and also generating additional components of stimulated polariton scattering in lithium niobate crystal having both cubic and quadratic nonlinearities. In this contribution we report on generation of more than two Stokes components of stimulated Raman scattering with different Raman shifts in the all-solid-state, synchronously pumped, extra-cavity Raman laser based on the Raman-active a-cut BaWO4 crystal excited by a mode-locked, 220 nJ, 36 ps, 150 MHz diode sidepumped Nd:GdVO4 laser generating at the wavelength of 1063 nm. Excitation by the pumping radiation polarized along the BaWO4 crystal optical axis resulted in the Raman generation with not only usual (925cm - 1), but also additional (332cm - 1) Raman shift. Besides the 1180-nm first and 1323 nm second Stokes components with the Raman shift of 925cm - 1 from the 1063nm fundamental laser wavelength, we have achieved generation of the additional 1227 nm Raman component with different Raman shift of 332cm - 1 from the 1180nm component. At the 1227 nm component the strongest 12-times pulse shortening from 36ps down to 3ps was obtained due to shorter dephasing time of this additional Raman line (3ps for the 332-cm - 1 line instead of 6.5ps for the 925cm - 1 line). It has to be also noted that the 1225 nm generation is intracavity pumped by the 1179 nm first Stokes component resulting in the strongest pulse shortening close to the 332cm -1 line dephasing time (3ps). Slope efficiency of three Stokes components generation exceeded 20%.
Numerical Evaluation of Parameter Correlation in the Hartmann-Tran Line Profile
Adkins, Erin M.; Reed, Zachary; Hodges, Joseph T.
2017-06-01
The partially correlated quadratic, speed-dependent hard-collision profile (pCqSDHCP), for simplicity referred to as the Hartmann-Tran profile (HTP), has been recommended as a generalized lineshape for high resolution spectroscopy. The HTP parameterizes complex collisional effects such as Dicke narrowing, speed dependent narrowing, and correlations between velocity-changing and dephasing collisions, while also simplifying to simpler profiles that are widely used, such as the Voigt profile. As advanced lineshape profiles are adopted by more researchers, it is important to understand the limitations that data quality has on the ability to retrieve physically meaningful parameters using sophisticated lineshapes that are fit to spectra of finite signal-to-noise ratio. In this work, spectra were simulated using the HITRAN Application Programming Interface (HAPI) across a full range of line parameters. Simulated spectra were evaluated to quantify the precision with which fitted lineshape parameters can be determined at a given signal-to-noise ratio, focusing on the numerical correlation between the retrieved Dicke narrowing frequency and the velocity-changing and dephasing collisions correlation parameter. Tran, H., N. Ngo, and J.-M. Hartmann, Journal of Quantitative Spectroscopy and Radiative Transfer 2013. 129: p. 89-100. Tennyson, et al., Pure Appl. Chem. 2014, 86: p. 1931-1943. Kochanov, R.V., et al., Journal of Quantitative Spectroscopy and Radiative Transfer 2016. 177: p. 15-30. Tran, H., N. Ngo, and J.-M. Hartmann, Journal of Quantitative Spectroscopy and Radiative Transfer 2013. 129: p. 199-203.
Coherent Rabi Dynamics of a Superradiant Spin Ensemble in a Microwave Cavity
Rose, B. C.; Tyryshkin, A. M.; Riemann, H.; Abrosimov, N. V.; Becker, P.; Pohl, H.-J.; Thewalt, M. L. W.; Itoh, K. M.; Lyon, S. A.
2017-07-01
We achieve the strong-coupling regime between an ensemble of phosphorus donor spins in a highly enriched 28Si crystal and a 3D dielectric resonator. Spins are polarized beyond Boltzmann equilibrium using spin-selective optical excitation of the no-phonon bound exciton transition resulting in N =3.6 ×1 013 unpaired spins in the ensemble. We observe a normal mode splitting of the spin-ensemble-cavity polariton resonances of 2 g √{N }=580 kHz (where each spin is coupled with strength g ) in a cavity with a quality factor of 75 000 (γ ≪κ ≈60 kHz , where γ and κ are the spin dephasing and cavity loss rates, respectively). The spin ensemble has a long dephasing time (T2*=9 μ s ) providing a wide window for viewing the dynamics of the coupled spin-ensemble-cavity system. The free-induction decay shows up to a dozen collapses and revivals revealing a coherent exchange of excitations between the superradiant state of the spin ensemble and the cavity at the rate g √{N }. The ensemble is found to evolve as a single large pseudospin according to the Tavis-Cummings model due to minimal inhomogeneous broadening and uniform spin-cavity coupling. We demonstrate independent control of the total spin and the initial Z projection of the psuedospin using optical excitation and microwave manipulation, respectively. We vary the microwave excitation power to rotate the pseudospin on the Bloch sphere and observe a long delay in the onset of the superradiant emission as the pseudospin approaches full inversion. This delay is accompanied by an abrupt π -phase shift in the peusdospin microwave emission. The scaling of this delay with the initial angle and the sudden phase shift are explained by the Tavis-Cummings model.
Carrier-phonon interaction in semiconductor quantum dots
Energy Technology Data Exchange (ETDEWEB)
Seebeck, Jan
2009-03-10
In recent years semiconductor quantum dots have been studied extensively due to their wide range of possible applications, predominantly for light sources. For successful applications, efficient carrier scattering processes as well as a detailed understanding of the optical properties are of central importance. The aims of this thesis are theoretical investigations of carrier scattering processes in InGaAs/GaAs quantum dots on a quantum-kinetic basis. A consistent treatment of quasi-particle renormalizations and carrier kinetics for non-equilibrium conditions is presented, using the framework of non-equilibrium Green's functions. The focus of our investigations is the interaction of carriers with LO phonons. Important for the understanding of the scattering mechanism are the corresponding quasi-particle properties. Starting from a detailed study of quantum-dot polarons, scattering and dephasing processes are discussed for different temperature regimes. The inclusion of polaron and memory effects turns out to be essential for the description of the carrier kinetics in quantum-dot systems. They give rise to efficient scattering channels and the obtained results are in agreement with recent experiments. Furthermore, a consistent treatment of the carrier-LO-phonon and the carrier-carrier interaction is presented for the optical response of semiconductor quantum dots, both giving rise to equally important contributions to the dephasing. Beside the conventional GaAs material system, currently GaN based light sources are of high topical interest due to their wide range of possible emission frequencies. In this material additionally intrinsic properties like piezoelectric fields and strong band-mixing effects have to be considered. For the description of the optical properties of InN/GaN quantum dots a procedure is presented, where the material properties obtained from an atomistic tight-binding approach are combined with a many-body theory for non
Petri net modeling of encrypted information flow in federated cloud
Khushk, Abdul Rauf; Li, Xiaozhong
2017-08-01
Solutions proposed and developed for the cost-effective cloud systems suffer from a combination of secure private clouds and less secure public clouds. Need to locate applications within different clouds poses a security risk to the information flow of the entire system. This study addresses this by assigning security levels of a given lattice to the entities of a federated cloud system. A dynamic flow sensitive security model featuring Bell-LaPadula procedures is explored that tracks and authenticates the secure information flow in federated clouds. Additionally, a Petri net model is considered as a case study to represent the proposed system and further validate the performance of the said system.
Hybrid Logical Analyses of the Ambient Calculus
DEFF Research Database (Denmark)
Bolander, Thomas; Hansen, René Rydhof
2007-01-01
In this paper, hybrid logic is used to formulate a rational reconstruction of a previously published control flow analysis for the mobile ambients calculus and we further show how a more precise flow-sensitive analysis, that takes the ordering of action sequences into account, can be formulated...... in a natural way. We show that hybrid logic is very well suited to express the semantic structure of the ambient calculus and how features of hybrid logic can be exploited to reduce the "administrative overhead" of the analysis specification and thus simplify it. Finally, we use HyLoTab, a fully automated...
DEFF Research Database (Denmark)
Kim, S.G.; Rostrup, Egill; Larsson, H.B.
1999-01-01
signal changes were measured simultaneously using the flow-sensitive alternating inversion recovery (FAIR) technique. During hypercapnia established by an end-tidal CO2 increase of 1.46 kPa, CBF in the visual cortex increased by 47.3 +/- 17.3% (mean +/- SD; n = 9), and deltaR2* was -0.478 +/- 0.147 sec......The blood oxygenation level-dependent (BOLD) effect in functional magnetic resonance imaging depends on at least partial uncoupling between cerebral blood flow (CBF) and cerebral metabolic rate of oxygen (CMRO2) changes. By measuring CBF and BOLD simultaneously, the relative change in CMRO2 can...
A congestion line flow control in deregulated power system
Directory of Open Access Journals (Sweden)
Venkatarajan Shanmuga Sundaram
2011-01-01
Full Text Available Under open access, market-driven transactions have become the new independent decision variables defining the behavior of the power system. The possibility of transmission lines getting over-loaded is relatively more under deregulated operation because different parts of the system are owned by separate companies and in part operated under varying service charges. This paper discusses a two-tier algorithm for correcting the lone overloads in conjunction with the conventional power-flow methods. The method uses line flow sensitivities, which are computed by the East Decoupled Power-flow algorithm and can be adapted for on-line implementation.
New methods for MR angiography
International Nuclear Information System (INIS)
Nishimura, D.G.; Pauly, J.M.; Macovski, A.; Jackson, J.I.; Conolly, S.M.
1986-01-01
The authors explored several methods of projection vessel imaging suitable for coronary arteries and vessels in the head and neck. To produce a vessel signal, one subtractive method varies the time-of-flight effects of blood flowing into an imaged slab by tagging different regions between measurements. A second method avoids a subtraction operation by using a sequence of pulses designed to excite flowing blood only. Manipulation of the imaging gradients to create velocity-dependent phase or magnitude changes can augment the flow sensitivity. In humans, these methods have demonstrated excellent static material, vessel contrast, and resolution
Energy Technology Data Exchange (ETDEWEB)
Popp, Antonia
2011-12-16
The experiments presented in this thesis study several aspects of electron acceleration in a laser-driven plasma wave. High-intensity lasers can efficiently drive a plasma wave that sustains electric fields on the order of 100 GV/m. Electrons that are trapped in this plasma wave can be accelerated to GeV-scale energies. As the accelerating fields in this scheme are 3-4 orders of magnitude higher than in conventional radio-frequency accelerators, the necessary acceleration distance can be reduced by the same factor, turning laser-wakefield acceleration (LWFA) into a promising compact, and potentially cheaper, alternative. However, laser-accelerated electron bunches have not yet reached the parameter standards of conventional accelerators. This work will help to gain better insight into the acceleration process and to optimize the electron bunch properties. The 25 fs, 1.8 J-pulses of the ATLAS laser at the Max-Planck-Institute of Quantum Optics were focused into a steady-state flow gas cell. This very reproducible and turbulence-free gas target allows for stable acceleration of electron bunches. Thus the sensitivity of electron parameters to subtle changes of the experimental setup could be determined with meaningful statistics. At optimized experimental parameters, electron bunches of {approx}50 pC total charge were accelerated to energies up to 450 MeV with a divergence of {approx}2 mrad FWHM. As, in a new design of the gas cell, its length can be varied from 2 to 14 mm, the electron bunch energy could be evaluated after different acceleration distances, at two different electron densities. From this evolution important acceleration parameters could be extracted. At an electron density of 6.43. 10{sup 18} cm{sup -3} the maximum electric field strength in the plasma wave was determined to be {approx}160 GV/m. The length after which the relativistic electrons outrun the accelerating phase of the electric field and are decelerated again, the so-called dephasing length
Theoretical models of the spin-dependent charge-carrier dynamics in metals and semiconductors
International Nuclear Information System (INIS)
Krauss, Michael
2010-01-01
This thesis is concerned with spin-dependent carrier dynamics in semiconductors and metals. We are especially interested in the dynamics on ultrashort timescales, which can be driven by ultrashort optical excitation, and use of a theoretical description in terms of the dynamical spin-density matrix. The first part of this thesis is concerned with spin-dependent carrier dynamics in bulk GaAs. For conduction electrons in GaAs, the most important mechanisms, by which an electron spin polarization can be destroyed, are the Dyakonov-Perel and Bir-Aronov-Pikus mechanisms. For the Dyakonov-Perel effect, our treatment is the first calculation of the dynamics of the spindensity matrix for bulk GaAs. From our microsopic calculation, we extract spin-dephasing times. In particular, we can describe the dependence of the spin-dephasing time for a wide range of n-doping concentrations and explain the spin-dephasing dynamics in and out of the motional-narrowing regime. For the Bir-Aronov-Pikus mechanism, i.e., the exchange interaction of electronics with holes, approximate relaxation times for limiting cases were derived about 30 years ago. We show that these approaches provide an incomplete picture of spin relaxation, and are only valid for high or low densities, whereas the microscopic calculation is capable of explaining the electronic dynamics also for intermediate doping densities, which are most interesting for typical experiments. The spin-dependent hole dynamics in GaAs is much faster than that of electrons, because the p-like hole bands experience the spin-orbit interaction directly, rather than through the interaction with other bands. The resulting spin relaxation is sometimes referred to as an Elliott-Yafet mechanism. For the first time, we present results for the microscopic dynamics of this mechanism for holes in bulk GaAs, and we discuss the different results that may be obtained with different measurement techniques. We also analyze the importance of ''spin hot
International Nuclear Information System (INIS)
Popp, Antonia
2011-01-01
The experiments presented in this thesis study several aspects of electron acceleration in a laser-driven plasma wave. High-intensity lasers can efficiently drive a plasma wave that sustains electric fields on the order of 100 GV/m. Electrons that are trapped in this plasma wave can be accelerated to GeV-scale energies. As the accelerating fields in this scheme are 3-4 orders of magnitude higher than in conventional radio-frequency accelerators, the necessary acceleration distance can be reduced by the same factor, turning laser-wakefield acceleration (LWFA) into a promising compact, and potentially cheaper, alternative. However, laser-accelerated electron bunches have not yet reached the parameter standards of conventional accelerators. This work will help to gain better insight into the acceleration process and to optimize the electron bunch properties. The 25 fs, 1.8 J-pulses of the ATLAS laser at the Max-Planck-Institute of Quantum Optics were focused into a steady-state flow gas cell. This very reproducible and turbulence-free gas target allows for stable acceleration of electron bunches. Thus the sensitivity of electron parameters to subtle changes of the experimental setup could be determined with meaningful statistics. At optimized experimental parameters, electron bunches of ∼50 pC total charge were accelerated to energies up to 450 MeV with a divergence of ∼2 mrad FWHM. As, in a new design of the gas cell, its length can be varied from 2 to 14 mm, the electron bunch energy could be evaluated after different acceleration distances, at two different electron densities. From this evolution important acceleration parameters could be extracted. At an electron density of 6.43. 10 18 cm -3 the maximum electric field strength in the plasma wave was determined to be ∼160 GV/m. The length after which the relativistic electrons outrun the accelerating phase of the electric field and are decelerated again, the so-called dephasing length, was found to be 4.9 mm
Electrical control of a long-lived spin qubit in a Si/SiGe quantum dot
Kawakami, Erika
2015-03-01
Electron spins in Si/SiGe quantum dots are one of the most promising candidates for a quantum bit for their potential to scale up and their long dephasing time. We realized coherent control of single electron spin in a single quantum dot (QD) defined in a Si/SiGe 2D electron gas. Spin rotations are achieved by applying microwave excitation to one of the gates, which oscillates the electron wave function back and forth in the gradient field produced by cobalt micromagnets fabricated near the dot. The electron spin is read out in single-shot mode via spin-to-charge conversion and a QD charge sensor. In earlier work, both the fidelity of single-spin rotations and the spin echo decay time were limited by a small splitting of the lowest two valleys. By changing the direction and magnitude of the external magnetic field as well as the gate voltages that define the dot potential, we were able to increase the valley splitting and also the difference in Zeeman splittings associated with these two valleys. This has resulted in considerable improvements in the gate fidelity and spin echo decay times. Thanks to the long intrinsic dephasing time T2* = 900 ns and Rabi frequency of 1.4 MHz, we now obtain an average single qubit gate fidelity of an electron spin in a Si/SiGe quantum dot of 99 percent, measured via randomized benchmarking. The dephasing time is extended to 70 us for the Hahn echo and up to 400 us with CPMG80. From the dynamical decoupling data, we extract the noise spectral density in the range of 30 kHz-3 MHz. We will discuss the mechanism that induces this noise and is responsible for decoherence. In parallel, we also realized electron spin resonance and coherent single-spin control by second harmonic generation, which means we can drive an electron spin at half the Larmor frequency. Finally, we observe not only single-spin transitions but also transitions whereby both the spin and the valley state are flipped. Altogether, these measurements have significantly
Investigation of Current Induced Spin Polarization in III-V Semiconductor Epilayers
Luengo-Kovac, Marta
In the development of a semiconductor spintronics device, a thorough understanding of spin dynamics in semiconductors is necessary. In particular, electrical control of electron spins is advantageous for its compatibility with present day electronics. In this thesis, we will discuss the electrical modification of the electron g-factor, which characterizes the strength of the interaction between a spin and a magnetic field, as well as investigate electrically generated spin polarizations as a function of various material parameters. We report on the modification of the electron g-factor by an in-plane electric field in an InGaAs epilayer. We performed external magnetic field scans of the Kerr rotation of the InGaAs film in order to measure the g-factor independently of the spin-orbit fields. The g-factor increases from -0.4473(0.0001) at 0 V/cm to -0.4419( 0.0001) at 50 V/cm applied along the [110] crystal axis. A comparison of temperature and voltage dependent photoluminescence measurements indicate that minimal channel heating occurs at these voltages. Possible explanations for this g-factor modification are discussed, including an increase in the electron temperature that is independent of the lattice temperature and the modification of the donor-bound electron wave function by the electric field. The current-induced spin polarization and momentum-dependent spin-orbit field were measured in InGaAs epilayers with varying indium concentrations and silicon doping densities. Samples with higher indium concentrations and carrier concentrations and lower mobilities were found to have larger electrical spin generation efficiencies. Furthermore, current-induced spin polarization was detected in GaAs epilayers despite the absence of measurable spin-orbit fields, indicating that the spin polarization mechanism is extrinsic. Temperature-dependent measurements of the spin dephasing rates and mobilities were used to characterize the relative strengths of the intrinsic D
Simprini, Lauren A; Afroz, Anika; Cooper, Mitchell A; Klem, Igor; Jensen, Christoph; Kim, Raymond J; Srichai, Monvadi B; Heitner, John F; Sood, Michael; Chandy, Elizabeth; Shah, Dipan J; Lopez-Mattei, Juan; Biederman, Robert W; Grizzard, John D; Fuisz, Anthon; Ghafourian, Kambiz; Farzaneh-Far, Afshin; Weinsaft, Jonathan
2014-09-01
Mitral regurgitation (MR) is an important complication after prosthetic mitral valve (PMV) implantation. Transthoracic echocardiography is widely used to screen for native MR, but can be limited with PMV. Cine-cardiac magnetic resonance (CMR) holds the potential for the non-invasive assessment of regurgitant severity based on MR-induced inter-voxel dephasing. The study aim was to evaluate routine cine-CMR for the visual assessment of PMV-associated MR. Routine cine-CMR was performed at nine sites. A uniform protocol was used to grade MR based on jet size in relation to the left atrium (mild 2/3). MR was graded in each long-axis orientation, with overall severity based on cumulative grade. Cine-CMR was also scored for MR density and pulmonary vein systolic flow reversal (PVSFR). Visual interpretation was compared to quantitative analysis in a single-center (derivation) cohort, and to transesophageal echocardiography (TEE) in a multicenter (validation) cohort. The population comprised 85 PMV patients (59% mechanical valves, 41% bioprostheses). Among the derivation cohort (n = 25), quantitative indices paralleled visual scores, with stepwise increases in jet size and density in relation to visually graded MR severity (both p = 0.001). Patients with severe MR had an almost three-fold increase in quantitative jet area (p = 0.002), and a two-fold increase in density (p = 0.04) than did other patients. Among the multicenter cohort, cine-CMR and TEE (Δ =. 2 ± 3 days) demonstrated moderate agreement (κ = 0.44); 64% of discordances differed by ≤ 1 grade (Δ = 1.2 ± 0.5). Using a TEE reference, cine-CMR yielded excellent diagnostic performance for severe MR (sensitivity, negative predictive value = 100%). Patients with visually graded severe MR also had more frequent PVSFR (p cine-CMR. Cine-CMR is useful for the assessment of PMV-associated MR, which manifests concordant quantitative and qualitative changes in size and density of inter-voxel dephasing. Visual MR
Simprini, Lauren A.; Afroz, Anika; Cooper, Mitchell A.; Klem, Igor; Jensen, Christoph; Kim, Raymond J.; Srichai, Monvadi B.; Heitner, John F.; Sood, Michael; Chandy, Elizabeth; Shah, Dipan J.; Lopez-Mattei, Juan; Biederman, Robert W.; Grizzard, John D.; Fuisz, Anthon; Ghafourian, Kambiz; Farzaneh-Far, Afshin; Weinsaft, Jonathan
2016-01-01
Background/Aim MR is an important complication after PMV. Transthoracic echocardiography is widely used to screen for native MR, but can be limited with PMV. Cine-CMR holds potential to non-invasively assess regurgitant severity based on MR-induced inter-voxel dephasing. This study evaluated routine cine-CMR for visual assessment of prosthetic mitral valve (PMV) associated mitral regurgitation (MR). Methods Routine cine-CMR was performed at 9 sites. A uniform protocol was used to grade MR based on jet size in relation to the left atrium (mild 2/3): MR was graded in each long axis orientation, with overall severity based on cumulative grade. Cine-CMR was also scored for MR density and pulmonary vein systolic flow reversal (PSFR). Visual interpretation was compared to quantitative analysis in a single center (derivation) cohort, and to transesophageal echocardiography (TEE) in a multicenter (validation) cohort. Results The population comprised 85 PMV patients (59% mechanical, 41% bioprosthetic). Among the derivation cohort (n=25), quantitative indices paralleled visual scores, with stepwise increases in jet size and density in relation to visually graded MR severity (both p=0.001): Patients with severe MR had nearly a 3-fold increase in quantitative jet area (p=0.002), and 2-fold increase in density (p=0.04) than did others. Among the multicenter cohort, cine-CMR and TEE (Δ=2±3 days) demonstrated moderate agreement (κ=0.44); 64% of discordances differed by ≤ 1 grade (Δ=1.2±0.5). Using a TEE reference, cine-CMR yielded excellent diagnostic performance for severe MR (sensitivity, negative predictive value=100%). Patients with visually graded severe MR also had more frequent PVSFR (pcine-CMR. Conclusions Cine-CMR is useful for assessment of PMV-associated MR, which manifests concordant quantitative and qualitative changes in size and density of inter-voxel dephasing. Visual MR assessment based on jet size provides an accurate non-invasive means of screening for
Energy Technology Data Exchange (ETDEWEB)
Weber, Carsten
2008-07-01
This work is focused on the optical dynamics of mesoscopic semiconductor heterostructures, using as prototypes zero-dimensional quantum dots and quantum cascade lasers which consist of quasitwo- dimensional quantum wells. Within a density matrix theory, a microscopic many-particle theory is applied to study scattering effects in these structures: the coupling to external as well as local fields, electron-phonon coupling, coupling to impurities, and Coulomb coupling. For both systems, the investigated effects are compared to experimentally observed results obtained during the past years. In quantum dots, the three-dimensional spatial confinement leads to the necessity to consider a quantum kinetic description of the dynamics, resulting in non-Markovian electron-phonon effects. This can be seen in the spectral phonon sidebands due to interaction with acoustic phonons as well as a damping of nonlinear Rabi oscillations which shows a nonmonotonous intensity and pulse duration dependence. An analysis of the inclusion of the self-interaction of the quantum dot shows that no dynamical local field terms appear for the simple two-level model. Considering local fields which have their origin in many quantum dots, consequences for a two-level quantum dot such as a zero-phonon line broadening and an increasing signal in photon echo experiments are found. For the use of quantum dots in an optical spin control scheme, it is found that the dephasing due to the electron-phonon interaction can be dominant in certain regimes. Furthermore, soliton and breather solutions are studied analytically in nonlinear quantum dot ensembles. Generalizing to quasi-two-dimensional structures, the intersubband dynamics of quantum cascade laser structures is investigated. A dynamical theory is considered in which the temporal evolution of the subband populations and the current density as well as the influence of scattering effects is studied. In the nonlinear regime, the scattering dependence and
Hydrodynamic Modeling of Nokoué Lake in Benin
Directory of Open Access Journals (Sweden)
Josué Zandagba
2016-12-01
Full Text Available Nokoué Lake is a complex ecosystem, the understanding of which requires control of physical processes that have occurred. For this, the Surface Water Modeling System (SMS hydrodynamic model was calibrated and validated on the water depth data. The results of these simulations show a good match between the simulated and observed data for bottom roughness and turbulent exchange coefficients, of 0.02 m−1/3·s and 20 m2/s respectively. Once the ability of the model to simulate the hydrodynamics of the lake is testified, the model is used to simulate water surface elevation, exchanged flows and velocities. The simulation shows that the tidal amplitude is maximum at the inlet of the channel and decreases gradually from the inlet towards the lagoon’s main body. The propagation of the tidal wave is characterized by the dephasing and the flattening of the amplitude tide, which increases as we move away from the channel. This dephasing is characterized by a high and low tides delay of about 1 or 4 h and also depends on the tide amplitude and location. The velocities inside the lake are very low and do not exceed 0.03 m/s. The highest are obtained at the entrance of the channel. In a flood period, in contrast with the low-water period, incoming flows are higher than outflows, reinforced by the amplitude of the tide. An average renewal time of the lake has been estimated and corresponds during a flood period to 30 days for an average amplitude tide and 26.3 days on a high amplitude tide. In a low water period it is 40.2 days for an average amplitude tide and 30 days for a high amplitude tide. From the results obtained, several measures must be taken into account for the rational management of the lake water resources. These include a dam construction at the lake upstream, to control the river flows, and the dredging of the channel to facilitate exchanges with the sea.
Coherent properties of single quantum dot transitions and single photon emission
Energy Technology Data Exchange (ETDEWEB)
Ester, Patrick
2008-04-23
In this work, the properties and the different dephasing mechanisms of single QD transitions are analyzed. In addition, some applications are presented which arise due to the properties of the confined exciton. The isolation of a single QD out of the ensemble is achieved via near field shadow masks, which restricts excitation and QD luminescence to a single QD. The integration of a QD-layer into a diode structure allows for an analysis of various dephasing mechanisms of a confined electron hole pair. The single QD is characterized regarding the energy of nearly all possible transitions, e.g. the ground state, excited states, charged states, multiple occupations, and phonon assisted absorptions. A very important issue in this content is the voltage dependence of the transition energy and thereby the ability of tunneling processes of charge carriers in and out of the QD. The QD-states, which are subject of investigation here, are the single exciton ground state, the first excited state (p-shell), and the (GaAs-) LO (longitudinal optical) phonon assisted absorption. By applying a suitable voltage, the resonantly excited ground state exciton is able to decay by a tunneling process, which reflects the transition energy in the photocurrent spectra. The p-shell transition decays by a relaxation process into the ground state, followed by an optical recombination process. The phonon assisted absorption differs from the p-shell transition. The resonant excitation energy fits to the exciton ground state energy plus the energy of a GaAs LO phonon. In this case, the single exciton (ground state) is generated as well as a GaAs LO phonon. These three states are investigated in different respects, such as different applied voltages, excitation polarizations, excitation intensities, and coherent properties. The LO-assisted absorption shows also a saturation behavior. The exciton in the QD is able to interfere with the second laser pulse due to the storage of the phase information
Exciton-polariton dynamics in quantum dot-cavity system
Energy Technology Data Exchange (ETDEWEB)
Neto, Antonio F.; Lima, William J.; Villas-Boas, Jose M. [Universidade Federal de Uberlandia (UFU), MG (Brazil). Inst. de Fisica
2012-07-01
Full text: One of the basic requirement for quantum information processing systems is the ability to completely control the state of a single qubit. This imply in know all sources of decoherence and elaborate ways to avoid them. In recent work, A. Laucht et al. [1] presented detailed theoretical and experimental investigations of electrically tunable single quantum dot (QD) - photonic crystal (PhC) nanocavity systems operating in the strong coupling regime of the light matter interaction. Unlike previous studies, where the exciton-cavity spectral detuning was varied by changing the lattice temperature, or by the adsorption of inert gases at low temperatures, they employ the quantum confined Stark-effect to electro-optically control the exciton-cavity detuning. The new built device enabled them to systematically probe the emission spectrum of the strongly coupled system as a function of external control parameters, as for example the incoherent excitation power density or the lattice temperature. Those studies reveal for the first time insights in dephasing mechanisms of 0D exciton polaritons [1]. In another study [2], using a similar device, they investigate the coupling between two different QDs with a single cavity mode. In both works, incoherent pumping was used, but for quantum information, coherent and controlled excitations are necessary. Here, we theoretically investigate the dynamics a single quantum dot inside a cavity under coherent pulse excitation and explore a wide range of parameters, as for example, the exciton-cavity detunings, the excitation power, the spontaneous decay, and pure dephasing. We use density matrix formalism in the Lindblad form, and we solve it numerically. Our results show that coherent excitation can be used to probe strong coupling between exciton and cavity mode by monitoring the exciton Rabi oscillation as function of the cavity detuning. This can give new insights for future experimental measurement focusing on quantum
Spin-transport-phenomena in metals, semiconductors, and insulators
Energy Technology Data Exchange (ETDEWEB)
Althammer, Matthias Klaus
2012-07-19
Assuming that one could deterministically inject, transport, manipulate, store and detect spin information in solid state devices, the well-established concepts of charge-based electronics could be transferred to the spin realm. This thesis explores the injection, transport, manipulation and storage of spin information in metallic conductors, semiconductors, as well as electrical insulators. On the one hand, we explore the spin-dependent properties of semiconducting zinc oxide thin films deposited via laser-molecular beam epitaxy (laser-MBE). After demonstrating that the zinc oxide films fabricated during this thesis have excellent structural, electrical, and optical properties, we investigate the spin-related properties by optical pump/probe, electrical injection/optical detection, and all electrical spin valve-based experiments. The two key results from these experiments are: (i) Long-lived spin states with spin dephasing times of 10 ns at 10 K related to donor bound excitons can be optically addressed. (ii) The spin dephasing times relevant for electrical transport-based experiments are {<=} 2 ns at 10 K and are correlated with structural quality. On the other hand we focus on two topics of current scientific interest: the comparison of the magnetoresistance to the magnetothermopower of conducting ferromagnets, and the investigation of pure spin currents generated in ferromagnetic insulator/normal metal hybrid structures. We investigate the magnetoresistance and magnetothermopower of gallium manganese arsenide and Heusler thin films as a function of external magnetic field orientation. Using a series expansion of the resistivity and Seebeck tensors and the inherent symmetry of the sample's crystal structure, we show that a full quantitative extraction of the transport tensors from such experiments is possible. Regarding the spin currents in ferromagnetic insulator/normal metal hybrid structures we studied the spin mixing conductance in yttrium iron garnet
Saitow, Ken-ichi; Sasaki, Jungo
2005-03-08
The short-range structure of supercritical methanol (CH(3)OH) is investigated by measuring the spontaneous Raman spectra of the C-O stretching mode. The spectra are obtained at a reduced temperature, T(r)=T/T(c)=1.02 (522.9 K), which permits the neat fluid to be studied isothermally as a function of density. As the density increases, the spectral peaks shift toward the lower energy side and the spectra broaden. In the supercritical region, the amount of shifting shows nonlinear density dependence and the width becomes anomalously large. We use the perturbed hard-sphere model to analyze these density dependencies along the vibrational coordinate. The amount of shifting is decomposed into attractive and repulsive components, and the changes in attractive and repulsive energies are evaluated as functions of density and packing fraction, both of which are continuously varied by a factor of 120. Here we show that the shift amount consists principally of the attractive component at all densities, since the attractive energy is about eight times the repulsive energy. The density dependence of the widths is analyzed by calculating homogeneous and inhomogeneous widths as a function of density. The results show that, although vibrational dephasing and density inhomogeneity contribute similarly to the width at low and middle densities, at high density the main contributor turns out to be the vibrational dephasing. We estimate the local density enhancements of supercritical CH(3)OH as function of bulk density by two methods. The results of these analyses show common features, and both the estimated local density enhancements of CH(3)OH are considerably larger than the local density enhancements of simple fluids, i.e., those having nonhydrogen bonding. It is revealed that the local density of supercritical CH(3)OH is 40%-60% greater than the local densities of the simple fluids. We also estimate the local density fluctuation using the obtained values of attractive shift
Coherent properties of single quantum dot transitions and single photon emission
International Nuclear Information System (INIS)
Ester, Patrick
2008-01-01
In this work, the properties and the different dephasing mechanisms of single QD transitions are analyzed. In addition, some applications are presented which arise due to the properties of the confined exciton. The isolation of a single QD out of the ensemble is achieved via near field shadow masks, which restricts excitation and QD luminescence to a single QD. The integration of a QD-layer into a diode structure allows for an analysis of various dephasing mechanisms of a confined electron hole pair. The single QD is characterized regarding the energy of nearly all possible transitions, e.g. the ground state, excited states, charged states, multiple occupations, and phonon assisted absorptions. A very important issue in this content is the voltage dependence of the transition energy and thereby the ability of tunneling processes of charge carriers in and out of the QD. The QD-states, which are subject of investigation here, are the single exciton ground state, the first excited state (p-shell), and the (GaAs-) LO (longitudinal optical) phonon assisted absorption. By applying a suitable voltage, the resonantly excited ground state exciton is able to decay by a tunneling process, which reflects the transition energy in the photocurrent spectra. The p-shell transition decays by a relaxation process into the ground state, followed by an optical recombination process. The phonon assisted absorption differs from the p-shell transition. The resonant excitation energy fits to the exciton ground state energy plus the energy of a GaAs LO phonon. In this case, the single exciton (ground state) is generated as well as a GaAs LO phonon. These three states are investigated in different respects, such as different applied voltages, excitation polarizations, excitation intensities, and coherent properties. The LO-assisted absorption shows also a saturation behavior. The exciton in the QD is able to interfere with the second laser pulse due to the storage of the phase information
4D-MR flow analysis in patients after repair for tetralogy of Fallot
International Nuclear Information System (INIS)
Geiger, J.; Markl, M.; Jung, B.; Langer, M.; Grohmann, J.; Stiller, B.; Arnold, R.
2011-01-01
Comprehensive analysis of haemodynamics by 3D flow visualisation and retrospective flow quantification in patients after repair of tetralogy of Fallot (TOF). Time-resolved flow-sensitive 4D MRI (spatial resolution ∝ 2.5 mm, temporal resolution = 38.4 ms) was acquired in ten patients after repair of TOF and in four healthy controls. Data analysis included the evaluation of haemodynamics in the aorta, the pulmonary trunk (TP) and left (lPA) and right (rPA) pulmonary arteries by 3D blood flow visualisation using particle traces, and quantitative measurements of flow velocity. 3D visualisation of whole heart haemodynamics provided a comprehensive overview on flow pattern changes in TOF patients, mainly alterations in flow velocity, retrograde flow and pathological vortices. There was consistently higher blood flow in the rPA of the patients (rPA/lPA flow ratio: 2.6 ± 2.5 vs. 1.1 ± 0.1 in controls). Systolic peak velocity in the TP was higher in patients (1.9 m/s ± 0.7 m/s) than controls (0.9 m/s ± 0.1 m/s). 4D flow-sensitive MRI permits the comprehensive evaluation of blood flow characteristics in patients after repair of TOF. Altered flow patterns for different surgical techniques in the small patient cohort may indicate its value for patient monitoring and potentially identifying optimal surgical strategies. (orig.)
4D-MR flow analysis in patients after repair for tetralogy of Fallot
Energy Technology Data Exchange (ETDEWEB)
Geiger, J.; Markl, M.; Jung, B.; Langer, M. [University Hospital Freiburg, Department of Radiology, Medical Physics, Freiburg (Germany); Grohmann, J.; Stiller, B.; Arnold, R. [University Hospital Freiburg, Department of Congenital Heart Disease and Pediatric Cardiology, Freiburg (Germany)
2011-08-15
Comprehensive analysis of haemodynamics by 3D flow visualisation and retrospective flow quantification in patients after repair of tetralogy of Fallot (TOF). Time-resolved flow-sensitive 4D MRI (spatial resolution {proportional_to} 2.5 mm, temporal resolution = 38.4 ms) was acquired in ten patients after repair of TOF and in four healthy controls. Data analysis included the evaluation of haemodynamics in the aorta, the pulmonary trunk (TP) and left (lPA) and right (rPA) pulmonary arteries by 3D blood flow visualisation using particle traces, and quantitative measurements of flow velocity. 3D visualisation of whole heart haemodynamics provided a comprehensive overview on flow pattern changes in TOF patients, mainly alterations in flow velocity, retrograde flow and pathological vortices. There was consistently higher blood flow in the rPA of the patients (rPA/lPA flow ratio: 2.6 {+-} 2.5 vs. 1.1 {+-} 0.1 in controls). Systolic peak velocity in the TP was higher in patients (1.9 m/s {+-} 0.7 m/s) than controls (0.9 m/s {+-} 0.1 m/s). 4D flow-sensitive MRI permits the comprehensive evaluation of blood flow characteristics in patients after repair of TOF. Altered flow patterns for different surgical techniques in the small patient cohort may indicate its value for patient monitoring and potentially identifying optimal surgical strategies. (orig.)
Biomimetic micromechanical adaptive flow-sensor arrays
Krijnen, Gijs; Floris, Arjan; Dijkstra, Marcel; Lammerink, Theo; Wiegerink, Remco
2007-05-01
We report current developments in biomimetic flow-sensors based on flow sensitive mechano-sensors of crickets. Crickets have one form of acoustic sensing evolved in the form of mechanoreceptive sensory hairs. These filiform hairs are highly perceptive to low-frequency sound with energy sensitivities close to thermal threshold. In this work we describe hair-sensors fabricated by a combination of sacrificial poly-silicon technology, to form silicon-nitride suspended membranes, and SU8 polymer processing for fabrication of hairs with diameters of about 50 μm and up to 1 mm length. The membranes have thin chromium electrodes on top forming variable capacitors with the substrate that allow for capacitive read-out. Previously these sensors have been shown to exhibit acoustic sensitivity. Like for the crickets, the MEMS hair-sensors are positioned on elongated structures, resembling the cercus of crickets. In this work we present optical measurements on acoustically and electrostatically excited hair-sensors. We present adaptive control of flow-sensitivity and resonance frequency by electrostatic spring stiffness softening. Experimental data and simple analytical models derived from transduction theory are shown to exhibit good correspondence, both confirming theory and the applicability of the presented approach towards adaptation.
Directory of Open Access Journals (Sweden)
Stalder Aurelien F
2008-06-01
Full Text Available Abstract Aneurysm formation is a life-threatening complication after operative therapy in coarctation. The identification of patients at risk for the development of such secondary pathologies is of high interest and requires a detailed understanding of the link between vascular malformation and altered hemodynamics. The routine morphometric follow-up by magnetic resonance angiography is a well-established technique. However, the intrinsic sensitivity of magnetic resonance (MR towards motion offers the possibility to additionally investigate hemodynamic consequences of morphological changes of the aorta. We demonstrate two cases of aneurysm formation 13 and 35 years after coarctation surgery based on a Waldhausen repair with a subclavian patch and a Vosschulte repair with a Dacron patch, respectively. Comprehensive flow visualization by cardiovascular MR (CMR was performed using a flow-sensitive, 3-dimensional, and 3-directional time-resolved gradient echo sequence at 3T. Subsequent analysis included the calculation of a phase contrast MR angiography and color-coded streamline and particle trace 3D visualization. Additional quantitative evaluation provided regional physiological information on blood flow and derived vessel wall parameters such as wall shear stress and oscillatory shear index. The results highlight the individual 3D blood-flow patterns associated with the different vascular pathologies following repair of aortic coarctation. In addition to known factors predisposing for aneurysm formation after surgical repair of coarctation these findings indicate the importance of flow sensitive CMR to follow up hemodynamic changes with respect to the development of vascular disease.