Juan Mauricio Torres, Emerson Sadurni, Thomas H. Seligman
We present a simple exactly solvable extension of of the Jaynes-Cummings model by adding dissipation. This is done such that the total number of excitations is conserved. The Liouville operator in the resulting master equation can be reduced to blocks of $4\times 4$ matrices.
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We study the intrinsic decoherence of coupled harmonic oscillators. The Milburn master equation is solved exactly, and the dynamics of virtual ground state excitations are investigated. The interaction of quantum correlations and virtual excitation was then studied. The following is a summary of our major findings. (i) The damped oscillatory profile of all three quantities is the same. (ii) Ultra-strong coupling combined with huge anisotropy values results in the reemergence of entanglement and steering. (iii) To sustain entanglement and steering, virtual excitations are required. (iv) The qua…
Entangled photons from quantum-dot-cavity systems under non-Markovian decoherence by pulsed excitation
研究通过脉冲双光子共振激发量子点谐振腔系统，在非马尔可夫衰减条件下计算纠缠光子对的纠缠度，提出算法降低非马尔可夫动力学模拟的计算成本。
Decoherence of Single-Excitation Entanglement over DLCZ Quantum Networks Caused by Slow-Magnetic-Field Fluctuations and Protection Approach
本研究针对慢磁场涨落未被现有量子中继协议考虑的问题，构建含该噪声的自旋波模型并通过实验验证其会引发单激发纠缠退相干，提出方案将纠缠寿命从约135毫秒提升至约1.7秒。
We introduce Hermite polynomial excitation squeezed vacuum (SV) H_{n}(O)S(r)|0> with O=u a+v a^{+}. We investigate analytically the nonclassical properties according to Mandel's Q parameter, second correlation function, squeezing effect and the negativity of Wigner function (WF). It is found that all these nonclassicalities can be enhanced by H_{n}(O)operation and adjustable parameters u and v. In particular, the optimal negative volume delta_{opt}of WF can be achieved by modulating u and v for n>=2,while delta is kept unchanged for n=1. Furthermore, the decoherence effect of phase-sensitive e…
Violations of a Bell inequality are reported for an experiment where one of two entangled qubits is stored in a collective atomic memory for a user-defined time delay. The atomic qubit is found to preserve the violation of a Bell inequality for storage times up to 21 microseconds, 700 times longer than the duration of the excitation pulse that creates the entanglement. To address the question of the security of entanglement-based cryptography implemented with this system, an investigation of the Bell violation as a function of the cross-correlation between the generated nonclassical fields is …
Quantum Hall edge channels at integer filling factor provide a unique test-bench to understand decoherence and relaxation of single electronic excitations in a ballistic quantum conductor. In this Letter, we obtain a full visualization of the decoherence scenario of energy (Landau) and time (Levitov) resolved single electron excitations at filling factor $ν=2$. We show that the Landau excitation exhibits a fast relaxation followed by spin-charge separation whereas the Levitov excitation only experiences spin-charge separation. We finally suggest to use Hong-Ou-Mandel type experiments to probe …
Geometry versus excitation sector in the decoherence of asymmetric $N$-qubit $W$ states
该研究对比非对称N量子比特W态退相干中网络几何与激发扇区对两体纠缠的影响，推导噪声模型下的并发度动力学，明确两者为纠缠鲁棒性的独立控制要素。
Heralded entanglement between collective excitations in two atomic ensembles is probabilistically generated, stored, and converted to single photon fields. By way of the concurrence, quantitative characterizations are reported for the scaling behavior of entanglement with excitation probability and for the temporal dynamics of various correlations resulting in the decay of entanglement. A lower bound of the concurrence for the collective atomic state of 0.9\pm 0.3 is inferred. The decay of entanglement as a function of storage time is also observed, and related to the local dynamics.
A Mean-Field Lindblad Master Equation Framework for Interaction-Driven Decoherence in Solid-State Qubit Ensembles
提出多量子比特平均场Lindblad主方程框架，通过解析和数值方法研究相互作用、浓度、空间分布及噪声对固态量子比特弛豫和退相干时间的影响，并应用于Er³⁺掺杂CeO₂系统识别主导机制。
A theoretical model describing the Raman scattering process in atomic vapors is constructed. The treatment investigates the low-excitation regime suitable for modern experimental applications. Despite the incorporated decoherence effects (possibly mode dependent) it allows for a direct separation of the time evolution from the spatial degrees of freedom. The impact of noise on the temporal properties of the process is examined. The model is applied in two experimentally relevant situations of ultra-cold and room-temperature atoms. The spatial eigenmodes of the Stokes photons and their coupling…
We investigate cat codes that can correct multiple excitation losses and identify two types of logical errors: bit-flip errors due to excessive excitation loss and dephasing errors due to quantum back-action from the environment. We show that selected choices of logical subspace and coherent amplitude can efficiently reduce dephasing errors. The trade-off between the two major errors enables optimized performance of cat codes in terms of minimized decoherence. With high coupling efficiency, we show that one-way quantum repeaters with cat codes feature drastically boosted secure communication r…
We revisit the problem of decoherence of a qubit centrally coupled to an interacting spin environment, here modeled by a quantum compass chain or an extended XY model in a staggered magnetic field. These two models both support distinct spin liquid phases, adding a new element to the problem. By analyzing their Loschmidt echoes when perturbed by the qubit we find that a fast decoherence of the qubit is conditioned on the presence of propagating quasiparticles which couple to it. Different from expectations based on earlier works on central spin models, our result implies that the closeness of …
Sudden Decoherence by Resonant Particle Excitation for Testing Gravity-Induced Entanglement
本研究提出一种通过共振粒子激发引发突发退相干来探测引力诱导纠缠的新方法，利用浅势阱粒子与双频叠加简谐振子的引力相互作用，以粒子检测触发的退相干为纠缠证据，并探讨光力学实验实现方案。
We suggest a new method of studying coherence in finite level systems coupled to the environment and use it for the Hamiltonian that has been used to describe the light-harvesting pigment-protein complex. The method works with the adiabatic states and transforms the Hamiltonian to a form in which the terms responsible for decoherence and population relaxation are separated out. Decoherence is then accounted for non-perturbatively, and population relaxation using a Markovian master equation. Analytical results can be obtained for the seven level system and the calculations are very simple for s…
A general expression is derived for the momentum diffusion constant of a small polarizable particle in blackbody radiation, and is shown to be closely related to the long-wavelength collisional decoherence rate for such a particle in a thermal environment. We show how this diffusion constant appears in the steady-state photon emission rate of two dipoles induced by blackbody radiation. We consider in addition the Einstein--Hopf drag force on a small polarizable particle moving in a blackbody field, and derive its fully relativistic form from the Lorentz transformation of forces.
Surface Excitations, Energy Loss, and Decoherence in Electron Interferometry
本文建立了介电表面附近分束电子干涉测量中退相干的模式分辨描述，揭示了退相干率与电子能量损失谱的加权积分关系，并指出热权重可用于近场测温。
We present an all-optical implementation of quantum computation using semiconductor quantum dots. Quantum memory is represented by the spin of an excess electron stored in each dot. Two-qubit gates are realized by switching on trion-trion interactions between different dots. State selectivity is achieved via conditional laser excitation exploiting Pauli exclusion principle. Read-out is performed via a quantum-jump technique. We analyze the effect on our scheme's performance of the main imperfections present in real quantum dots: exciton decay, hole mixing and phonon decoherence. We introduce a…
We study decoherence of propagating spin-1/2 excitations in generic (non-integrable and/or disordered) spin chains. We find the relevant decoherence times to be shorter in both the near-critical and diffusive regimes (if any), which fact might have important implications for the recently proposed spin chain-based implementations of quantum information processing.
The interaction of (two-level) Rydberg atoms with dissipative QED cavity fields can be described classically or quantum mechanically, even for very low temperatures and mean number of photons, provided the damping constant is large enough. We investigate the quantum-classical border, the entanglement and decoherence of an analytically solvable model, analog to the atom-cavity system, in which the atom (field) is represented by a (driven and damped) harmonic oscillator. The maximum value of entanglement is shown to depend on the initial state and the dissipation-rate to coupling-constant ratio.…
In the framework of Lindblad theory for open quantum systems, we calculate the entropy of a damped quantum harmonic oscillator which is initially in a quasi-free state. The maximally predictable states are identified as those states producing the minimum entropy increase after a long enough time. In general, the states with a squeezing parameter depending on the environment's diffusion coefficients and friction constant are singled out, but if the friction constant is much smaller than the oscillator's frequency, coherent states (or thermalized coherent states) are obtained as the preferred cl…
We present and discuss a general density-matrix description of energy-dissipation and decoherence phenomena in open quantum systems, able to overcome the intrinsic limitations of the conventional Markov approximation. In particular, the proposed alternative adiabatic scheme does not threaten positivity at any time. The key idea of our approach rests in the temporal symmetrization and coarse graining of the scattering term in the Liouville-von Neumann equation, before applying the reduction procedure over the environment degrees of freedom. The resulting dynamics is genuinely Lindblad-like and …
We analyze the effects that general environments, namely ohmic and non-ohmic, at zero and high temperature induce over a quantum Brownian particle. We state that the evolution of the system can be summarized in terms of two main environmental induced physical phenomena: decoherence and energy activation. In this article we show that the latter is a post-decoherence phenomenon. As the energy is an observable, the excitation process is a direct indication of the system-environment entanglement particularly useful at zero temperature.
We study propagation of the decohering influence caused by a local measurement performed on a distributed quantum system. As an example, the gas of bosons forming a Bose-Einstein condensate is considered. We demonstrate that the local decohering perturbation exerted on the measured region propagates over the system in the form of a decoherence wave, whose dynamics is governed by elementary excitations of the system. We argue that the post-measurement evolution of the system (determined by elementary excitations) is of importance for transfer of decoherence, while the initial collapse of the wa…
We present a new method for the solution of the behavior of an ensemble of qubits in a random time-dependent external field. The forward evolution in time is governed by a transfer matrix. The elements of this matrix determine the various decoherence times. The method provides an exact solution in cases where the noise is piecewise constant in time. We show that it applies, for example, to a realistic model of decoherence of electron spins in semiconductors. Results are obtained for the non-perturbative regimes of the models, and we see a transition from weak relaxation to overdamped behavior …
We address the issue why a cosmological constant (dark energy) possesses a small positive value instead of being zero. Motivated by the cosmic landscape picture, we mimic the dark energy by a scalar field with potential wells and show that other degrees of freedom interacting with it can localize this field by decoherence in one of the wells. Dark energy can then acquire a small positive value. We also show that the additional degrees of freedom enhance the tunneling rate between the wells. The consideration is performed in detail for the case of two wells and then extended to a large number o…
Preparing and detecting spatially extended quantum superpositions of a massive object comprises an important fundamental test of quantum theory. These quantum states are extremely fragile and tend to quickly decay into incoherent mixtures due to the environmental decoherence. Experimental setups considered up to date address this threat in a conceptually straightforward way -- by eliminating the environment, i.e. by isolating an object in a sufficiently high vacuum. We show that another option exists: decoherence is suppressed in the presence of a strongly interacting environment if this envir…
The great success of point defects and dopants in semiconductors for quantum information processing has invigorated a search for molecules with analogous properties. Flexibility and tunability of desired properties in a large chemical space have great advantages over solid-state systems. The properties analogous to point defects were demonstrated in Cr(IV)-based molecular family, Cr(IV)(aryl)$_4$, where the electronic spin states were optically initialized, read out, and controlled. Despite this kick-start, there is still a large room for enhancing properties crucial for molecular qubits. Here…
Effects of finite trapping on the decay, recoil, and decoherence of dark states of quantum emitter arrays
本文研究了有限阱深和光介导力对量子发射体阵列中亚辐射态的影响，发现这些效应会导致衰减率随时间变化、振动能量转移及状态混合，并提出了通过优化阵列配置以减轻退相干的策略。
Fewest switches surface hopping with decoherence in the Marcus inverted regime: correct rates but wrong thermal populations
本研究指出，在马库斯倒置区域中，AFSSH方法能正确计算速率常数但存在热人口计算错误，通过分析推导揭示其机理。
If a magnetic polarization excess is locally injected in a crystal of interacting spins, this "excitation" would spread as consequence of spin-spin interactions. Such an apparently irreversible process is known as spin diffusion and it can lead the system back to "equilibrium". Even so, a unitary quantum dynamics would ensure a precise memory of the non-equilibrium initial condition. Then, if at certain time, say $t/2$, an experimental protocol reverses the many-body dynamics, it would drive the system back to the initial non-equilibrium state at time $t$. As a matter of fact, the reversal is …
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