Model for dissipative conductance in fractional quantum Hall states

We present a model of dissipative transport in the fractional quantum Hall regime. Our model takes account of tunneling through saddle points in the effective potential for excitations created by impurities. We predict the temperature range over which activated behavior is observed and explain why this range nearly always corresponds to around a factor two in temperature in both integer quantum Hall and fractional quantum Hall systems. We identify the ratio of the gap observed in the activated behavior and the temperature of the inflection point in the Arrhenius plot as an important diagnostic for determining the importance of tunneling in real samples.     

Detectability of dissipative motion in quantum vacuum via superradiance

We propose an experiment for generating and detecting vacuum-induced dissipative motion. A high frequency mechanical resonator driven in resonance is expected to dissipate mechanical energy in quantum vacuum via photon emission. The photons are stored in a high quality electromagnetic cavity and detected through their interaction with ultracold alkali-metal atoms prepared in an inverted population of hyperfine states. Superradiant amplification of the generated photons results in a detectable radio-frequency signal temporally distinguishable from the expected background.     

Accuracy for superposition of squeezed states in lossless and dissipative channel

The analysis of accuracy for superposition of squeezed states(SSSs) in lossless and loss case has been performed in this study.In lossless case,time accuracies of SSSs with mean photon number n s have a scaling of ns-2 in two limits of large and small squeezing.With the help of photon loss model,the dissipative channel will degrade accuracies has been proved.In the limit of large squeezing,the accuracy will slowly decrease with the reduction of transmittance.In the limit of small squeezing,time accuracy scales as 1/(η4ns2) and will decrease much faster along with decreases.     

Controlled quantum key distribution with three-photon polarization-entangled states via the collective noise channel

Using three-photon polarization-entangled GHZ states or W states, we propose controlled quantum key distribution protocols for circumventing two main types of collective noise, collective dephasing noise, or collective rotation noise. Irrespective of the number of controllers, a three-photon state can generate a one-bit secret key. The storage technique of quantum states is dispensable for the controller and the receiver, and it therefore allows performing the process in a more convenient mode. If the photon cost in a security check is disregarded, then the efficiency theoretically approaches unity.     

Perturbative expansion of quantum states of extended objects

We construct an effective Hamiltonian at fixed momentum which can be used to calculate higher-order corrections to quantum states of localized classical solutions of scalar field theories in 1 + 1 dimensions. We use the quantization scheme discussed first by Creutz and also by Rothe and one of the present authors (J.B.). The effective Hamiltonian is similar to, but nevertheless different from the one obtained in the collective coordinate method. The agreement of the energy corrections at the two-loop level has been checked.     

耗散腔中两二能级原子态的量子信息保真度

在能量耗散腔中,原子用泡利算符描述,光场用相干态描述,运用密度矩阵理论,得到了两二能级原子密度矩阵元的演化规律,针对不同的初态,分析与单模辐射场作用过程中原子态的量子信息保真度.结果表明:当两原子初始处于不同的量子态时,量子信息在传输过程中可能不失真或部分失真,也可能出现周期性演化;在输出态和输入态具有相同的纠缠度时,量子信息可能不失真,也可能完全失真.     

Evolution of a two-mode squeezed vacuum in the amplitude dissipative channel

For the first time we derive the dissipating result of an initial two-mode squeezed pure vacuum state passing through a two-mode amplitude dissipative channel described by the direct product of two independent single-mode master equations. Although these two master equations do not mix the two modes (there is no coupling between them), since the two-mode squeezed state is simultaneously an entangled state, the final state which emerges from passing this channel is a two-mode mixed density operator. The compact expression of the outcoming state is obtained, which manifestly shows that as time evolves, the squeezing effect decreases.     

Evolution of a two-mode squeezed vacuum in the amplitude dissipative channel

For the first time we derive the dissipating result of an initial two-mode squeezed pure vacuum state passing through a two-mode amplitude dissipative channel described by the direct product of two independent single-mode master equations. Although these two master equations do not mix the two modes (there is no coupling between them), since the two-mode squeezed state is simultaneously an entangled state, the final state which emerges from passing this channel is a two-mode mixed density operator. The compact expression of the outcoming state is obtained, which manifestly shows that as time evolves, the squeezing effect decreases.     

Evolution of the single-mode squeezed vacuum state in amplitude dissipative channel

Using the way of deriving infinitive sum representation of density operator as a solution to the master equation describing the amplitude dissipative channel by virtue of the entangled state representation, we show manifestly how the initial density operator of a single-mode squeezed vacuum state evolves into a definite mixed state which turns out to be a squeezed chaotic state with decreasing-squeezing and deeoherence. We investigate average photon number, photon statistics distributions for this mixed state.     

Reconstructing quantum states via quantum tomography and atom interferometry

Received: 25 July 1997     

Evolution law of a negative binomial state in an amplitude dissipative channel

For the first time we derive the evolution law of the negative binomial state In） （nI in an ampli-tude dissipative channel with a damping constant to. We find that after passing through the channel, the final state is still a negative binomial state, however the parameter γ evolves into The decay law of theaverage photon number is also obtained.     

Manipulating many-body quantum states via single-photon resonance

For an atomic Bose-Hubbard dimer quantum control via multiphoton processes have been investigated widely. We here explore how to manipulate the many-body quantum states via single-photon resonance by treating the periodic driving as a weak perturbation. The transition probabilities up to second-order approximation are given as functions of the driving parameters, which are considerable only for the single-photon resonance case. Due to some transition matrix elements vanishing, the first-order quantum transition obeys a selection rule. The non-forbidden transitions involve states of different entanglement entropies and all (part) of the forbidden transitions relate to the entropy balances between two states for odd (even) number of particles. The results provide a new route for manipulating many-body quantum states and entanglement entropies, and controlling the atomic tunnelings of the Bose-Hubbard dimer.     

Evolution of cat states in a dissipative parametric amplifier: decoherence and entanglement

The evolution of the Schr?dinger-cat states in a dissipative parametric amplifier is examined. The main tool in the analysis is the normally ordered characteristic function. Squeezing, photon-number distribution and reduced factorial moments are discussed for the single- and compound-mode cases. Also the single-mode Wigner function is demonstrated. In addition to the decoherence resulting from the interaction with the environment (damped case) there are two sources which can cause such decoherence in the system even if it is completely isolated: these are the decay of the pump and the relative phases of the initial cat states. Furthermore, for the damped case there are two regimes, which are underdamped and overdamped. In the first (second) regime the signal mode or the idler mode “collapses" to a statistical mixture (thermal field). Received 25 September 2001 / Received in final form 30 May 2002 Published online 13 December 2002 RID="a" ID="a"e-mail: sebaweh@awalnet.net.sa RID="b" ID="b"Joint Laboratory of Optics of Palacky University and Institute of Physics, Academy of Sciences of the Czech Republic, 17. listopadu 50, 772 07 Olomouc, Czech Republic.     

Entangled phase states via quantum beam splitter

We study the entanglement effect of beam splitter on the temporally stable phase states. Specifically, we consider the eigenstates (phase states) of a unitary phase operator resulting from the polar decomposition of ladder operators of generalized Weyl-Heisenberg algebras possessing finite dimensional representation space. The linear entropy that measures the degree of entanglement at the output of the beam splitter is analytically obtained. We find that the entanglement is not only strongly dependent on the Hilbert space dimension but also quite related to strength the parameter ensuring the temporal stability of the phase states. Finally, we discuss the evolution of the entangled phase states.     

Non-Gaussian quantum states generation and robust quantum non-Gaussianity via squeezing field

Recent studies show that quantum non-Gaussian states or using non-Gaussian operations can improve entanglement distillation, quantum swapping, teleportation, and cloning. In this work, employing a strategy of non-Gaussian operations(namely subtracting and adding a single photon), we propose a scheme to generate non-Gaussian quantum states named single-photon-added and-subtracted coherent(SPASC) superposition states by implementing Bell measurements, and then investigate the corresponding nonclassical features. By squeezed the input field, we demonstrate that robustness of nonGaussianity can be improved. Controllable phase space distribution offers the possibility to approximately generate a displaced coherent superposition states(DCSS). The fidelity can reach up to F ≥ 0.98 and F ≥ 0.90 for size of amplitude z = 1.53 and 2.36, respectively.     

Preservation of quantum states via a super-Zeno effect on ensemble quantum computers

Following a recent proposal by Dhar et al (2006 Phys. Rev. Lett. 96 100405), we demonstrate experimentally the preservation of quantum states in a two-qubit system based on a super-Zeno effect using liquid-state nuclear magnetic resonance techniques. Using inverting radiofrequency pulses and delicately selecting time intervals between two pulses, we suppress the effect of decoherence of quantum states. We observe that preservation of the quantum state |11\rg with the super-Zeno effect is three times more efficient than the ordinary one with the standard Zeno effect.