Publisher's Note: Quantum Fisher information of the Greenberger-Horne-Zeilinger state in decoherence channels [Phys. Rev. A 84, 022302 (2011)]
No abstract prepared.
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Engineering topics
Sun, C P
Publications and source records attributed to Sun, C P.
Quantum Fisher information of the Greenberg-Horne-Zeilinger state in decoherence channels
Quantum Fisher information of a parameter characterizes the sensitivity of the state with respect to changes of the parameter. In this article, we study the quantum Fisher information of a state with respect to SU(2) rotations under three decoherence channels: the amplitude-damping, phase-damping, and depolarizing channels. The initial state is chosen to be a Greenberg-Horne-Zeilinger state of which the phase sensitivity can achieve the Heisenberg limit. By using the Kraus operator representation, the quantum Fisher information is obtained analytically. We observe the decay and sudden change of the quantum Fisher information in all three channels.
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Multistability of electromagnetically induced transparency in atom-assisted optomechanical cavities
We study how an oscillating mirror affects the electromagnetically induced transparency (EIT) of an atomic ensemble confined in a gas cell, which is placed inside a microcavity with an oscillating mirror in one end. The cavity field acts as a probe of the EIT system and also produces a light pressure on the mirror. The back-action from the mirror to the cavity field results in several (from one to five) steady-states for this atom-assisted optomechanical cavity, producing a complex structure in its EIT. The multiequilibrium positions of the oscillating mirror have been calculated, and then the susceptibility is studied with respect to the different equilibrium positions. We find that the EIT of the atomic ensemble can be significantly changed by the oscillating mirror, and also the various steady states of the mirror have different effects on the EIT.
74 ATOMIC AND MOLECULAR PHYSICS↗
Analog of the electromagnetically-induced-transparency effect for two nanomechanical or micromechanical resonators coupled to a spin ensemble
We study a hybrid nanomechanical system coupled to a spin ensemble as a quantum simulator to favor a quantum interference effect, electromagnetically induced transparency (EIT). This system consists of two nanomechanical resonators (NAMRs), each of which is coupled to a nuclear spin ensemble, and can be regarded as a crucial element in the quantum network of NAMR arrays coupled to spin ensembles. Here, the nuclear spin ensembles behave as a long-lived transducer to store and transfer the NAMRs' quantum information. This system shows the analog of the EIT effect under the driving of a probe microwave field. The double EIT phenomenon emerges in the large-N (the number of nuclei) limit within the low excitation approximation, because the interactions between the spin ensemble and the two NAMRs are reduced to the coupling of three harmonic oscillators. Furthermore, the group velocity is reduced in the two absorption windows.
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Dispersive-coupling-based quantum Zeno effect in a cavity-QED system
We present a dispersive-coupling-based interpretation for the quantum Zeno effect (QZE) where measurements are dynamically treated as dispersive couplings of the measured system to the apparatus rather than the von Neumann's projections. It is found that the explicit dependence of the survival probability on the decoherence time quantitatively distinguishes this dynamic QZE from the usual one based on projection measurements. By revisiting the cavity-QED experiment of the QZE [J. Bernu et al., Phys. Rev. Lett. 101, 180402 (2008)], we suggest an alternative scheme to verify our theoretical consideration that frequent measurements slow down the increase of photon number inside a microcavity due to the nondemolition couplings with the atoms in large detuning.
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Multiatomic mirror for perfect reflection of single photons in a wide band of frequency
A resonant two-level atom doped in a one-dimensional waveguide behaves as a mirror, but this single-atom ''mirror'' can only reflect single photons perfectly at a specific frequency. For a one-dimensional coupled-resonator waveguide, we propose to extend the perfect-reflection region from a specific frequency point to a wide band by placing many atoms individually in the resonators in a finite coordinate region of the waveguide. Such a doped resonator array promises to control the propagation of a practical photon wave packet with a certain momentum distribution instead of a single photon, which is ideally represented by a plane wave with a specific momentum. The studies based on the discrete-coordinate scattering theory indicate that such a hybrid structure with finite atoms indeed provides a near-perfect reflection for a single photon in a wide band. We also calculated the photon group velocity distribution, which shows that the perfect-reflection wide band exactly corresponds to the stopping light region.
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Coherent excitation-energy transfer and quantum entanglement in a dimer
We study coherent energy transfer of a single excitation and quantum entanglement in a dimer, which consists of a donor and an acceptor modeled by two two-level systems. Between the donor and the acceptor, there exists a dipole-dipole interaction, which provides the physical mechanism for coherent energy transfer and entanglement generation. The donor and the acceptor couple to two independent heat baths with diagonal couplings that do not dissipate the energy of the noncoupling dimer. Special attention is paid to the effect on single-excitation energy transfer and entanglement generation of the energy detuning between the donor and the acceptor and the temperatures of the two heat baths. It is found that, the probability for single-excitation energy transfer largely depends on the energy detuning in the low temperature limit. Concretely, the positive and negative energy detunings can increase and decrease the probability at steady state, respectively. In the high temperature limit, however, the effect of the energy detuning on the probability is negligibly small. We also find that the probability is negligibly dependent on the bath temperature difference of the two heat baths. In addition, it is found that quantum entanglement can be generated in the process of coherent energy transfer. As the bath temperature increases, the generated steady-state entanglement decreases. For a given bath temperature, the steady-state entanglement decreases with the increase of the absolute value of the energy detuning.
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Quantum Fisher information flow and non-Markovian processes of open systems
We establish an information-theoretic approach for quantitatively characterizing the non-Markovianity of open quantum processes. Here, the quantum Fisher information (QFI) flow provides a measure to statistically distinguish Markovian and non-Markovian processes. A basic relation between the QFI flow and non-Markovianity is unveiled for quantum dynamics of open systems. For a class of time-local master equations, the exactly analytic solution shows that for each fixed time the QFI flow is decomposed into additive subflows according to different dissipative channels.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Qubit-induced phonon blockade as a signature of quantum behavior in nanomechanical resonators
The observation of quantized nanomechanical oscillations by detecting femtometer-scale displacements is a significant challenge for experimentalists. We propose that a phonon blockade can serve as a signature of quantum behavior in nanomechanical resonators. In analogy to the photon blockade and Coulomb blockade for electrons, the main idea for phonon blockade is that the second phonon cannot be excited when there is one phonon in the nonlinear oscillator. To realize phonon blockade, a superconducting quantum two-level system is coupled to the nanomechanical resonator and is used to induce the phonon self-interaction. Using Monte Carlo simulations, the dynamics of the induced nonlinear oscillator is studied via the Cahill-Glauber s-parametrized quasiprobability distributions. We show how the oscillation of the resonator can occur in the quantum regime and demonstrate how the phonon blockade can be observed with the currently accessible experimental parameters.
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Adiabatic creation of atomic squeezing in dark states versus decoherences
We study the multipartite correlations of the multiatom dark states, which are characterized by the atomic squeezing beyond the pairwise entanglement. It is shown that, in the photon storage process with atomic ensemble via the electromagnetically induced transparency (EIT) mechanism, the atomic squeezing and the pairwise entanglement can be created by adiabatically manipulating the Rabi frequency of the classical light field on the atomic ensemble. We also consider the sudden death for the atomic squeezing and the pairwise entanglement under various decoherence channels. An optimal time for generating the greatest atomic squeezing and pairwise entanglement is obtained by studying in detail the competition between the adiabatic creation of quantum correlation in the atomic ensemble and the decoherence that we describe with three typical decoherence channels.
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Bloch oscillations of polaritons of an atomic ensemble in magnetic fields
We study a washboard potential in a light-driven ensemble of three-level atoms induced by the externally applied magnetic fields under electromagnetically induced transparency (EIT). We find that a dark-state polariton, which is formed by an atomic ensemble dressed by the photon can display a typical quantum interference effect (i.e., the quasiparticle Bloch oscillation). The dark-state polariton is subjected to a washboard configuration potential with a spatially uniform force and a periodic potential provided by the linearly and periodically external magnetic fields, respectively. Due to the slower group velocity of the photons in the EIT medium, the period of Bloch oscillation can achieve a millisecond order of magnitude. Also, in our protocol, the Bloch oscillation of the dark-state polariton is feasibly modulated through the applied control and magnetic fields.
74 ATOMIC AND MOLECULAR PHYSICS↗
Single-particle machine for quantum thermalization
The long time accumulation of the random actions of a single particle 'reservoir' on its coupled system can transfer some temperature information of its initial state to the coupled system. This dynamic process can be referred to as a quantum thermalization in the sense that the coupled system can reach a stable thermal equilibrium with a temperature equal to that of the reservoir. We illustrate this idea based on the usual micromaser model, in which a series of initially prepared two-level atoms randomly pass through an electromagnetic cavity. It is found that, when the randomly injected atoms are initially prepared in a thermal equilibrium state with a given temperature, the cavity field will reach a thermal equilibrium state with the same temperature as that of the injected atoms. As in two limit cases, the cavity field can be cooled and 'coherently heated' as a maser process, respectively, when the injected atoms are initially prepared in ground and excited states. Especially, when the atoms in equilibrium are driven to possess some coherence, the cavity field may reach a higher temperature in comparison with the injected atoms. We also point out a possible experimental test for our theoretical prediction based on a superconducting circuit QED system.
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Controlling the transport of single photons by tuning the frequency of either one or two cavities in an array of coupled cavities
We theoretically study how to control transport, bound states, and resonant states of a single photon in a one-dimensional coupled-cavity array. We find that the transport of a single photon in the cavity array can be controlled by tuning the frequency of either one or two cavities. If one of the cavities in the array has a tunable frequency, and its frequency is tuned to be larger (or smaller) than those of other cavities, then there is a photon bound state above (or below) the energy band of the coupled-cavity array. However, if two cavities in the array have tunable frequencies, then there exist both bound states and resonant states. If the frequencies of the two cavities are chosen to be much larger than those of other cavities, and the hopping couplings between any two nearest-neighbor cavities are weak, then a single photon with a resonant wave vector can be trapped in the region between the two frequency-tunable cavities. In this case, a quantum supercavity can be formed by these two frequency-tunable cavities. We also study how to apply this photon transport control to an array of coupled superconducting transmission line resonators.
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