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The efficacy of dexmedetomidine in the prevention of postoperative delirium (POD) remains ambiguous, however, it has been used to reduce the incidence of delirium in elderly patients. Here, we conducted a meta-analysis study for assessing the effects of dexmedetomidine on POD among elderly patients following non-cardiac surgery. A systematic literature search was performed against the PubMed, EMBASE, Cochrane Library, and Web of Science databases, and all relevant literature published till November 30, 2019, were considered. Our analysis included 16 randomised controlled trials conducted with 4534 patients for exploring the effects of dexmedetomidine on POD in elderly patients following non-cardiac surgery. It was observed that the overall incidence of POD was significantly lower in the dexmedetomidine group than in the control group (risk ratio [RR] 0.51, 95% confidence interval [CI] 0.43-0.61, P < .01). Similar results were obtained from subgroup analysis upon comparison of the placebo (RR 0.52, 95% CI 0.41-0.66, P < .01, moderate quality of evidence), propofol-treated (RR 0.55, 95% CI 0.38-0.78, P < .01, low quality of evidence), and midazolam-treated (RR 0.38, 95% CI 0.20-0.71, P < .01, low quality of evidence) groups. Trial sequential analysis revealed that the cumulative z-value superseded the monitoring boundary and reached the required information size. However, patients who received dexmedetomidine had a higher incidence of bradycardia and hypotension. In conclusion, the meta-analysis revealed that dexmedetomidine appears to decrease the risk of POD in elderly patients following non-cardiac surgery. However, as some of the studies were heterogeneous and of low quality, high-quality trials are necessary for drawing more definitive conclusions.

Electromagnetically induced transparency (EIT) in quantum dot exciton systems in which the exciton behaves as a two-level system is investigated theoretically. It is shown that due to strong exciton–phonon coupling EIT can occur in such a quantum dot system and ultraslow light can propagate. The nonlinear optical absorption and Kerr coefficient based on EIT are also calculated. The numerical results show that giant nonlinear optical effects can be obtained while the frequency of the signal field differs only by an amount of LO phonon frequency from the exciton frequency in quantum dot systems.

The quantum oscillations of population in an optically driven asymmetrical double quantum dot device coupled to phonons are investigated theoretically and an analytical result is obtained. It shows that, even at zero temperature, the phonon effect is considerable. The Rabi frequency and tunneling rate between two dots are renormalized by a factor and its square, respectively. The ideal Rabi oscillation is changed into a beat pattern.

The decoherence of a central spin in an antiferromagnetic environment is investigated theoretically in terms of the spin wave approximation. It is analytically shown that the decoherence factor which displays a Gaussian decay strongly depends on the quantum correlations and the structure of the environment. The relation between the decoherence factor and the environmental temperature is also given explicitly.

Using the spin wave approximation, we study the entanglement of a two-spin system in an antiferromagnetic environment. It is shown analytically that the concurrence of the two-spin system displays a Gaussian decay and depends on the quantum correlations and the structure of the environment. The relation between the concurrence and the environmental temperature is given explicitly.

Taking electron–phonon interaction into consideration, we analyze the dynamical behavior of a radiated quantum dot molecule with two interacting electrons in it. The results show that the electron–phonon interaction modifies the conditions of single-electron and two-electron resonance and plays an important role on the evolution of the quantum system even at zero temperature.

For two coupled identical quantum dots in a two-mode cavity, we determine the conditions of two-photon and single-photon resonance. It is shown that the exciton-phonon interaction reduces the Rabi frequencies of each model and the Forster interaction between double quantum dots even at absolute zero temperature. The exciton-phonon interaction also makes a contribution to the static exciton-exciton dipole interaction energy. Furthermore, the additional interactions can modify the conditions of photon resonance significantly. A more realistic case of two nonidentical quantum dots is also considered. The influence of parameter misfits on the quantum system is discussed.

For two coupled quantum dots within cavity QED, we show that the exciton–phonon interaction reduces the Rabi frequency and Forster interaction even at absolute zero temperature. The exciton–phonon interaction also makes an additional contribution to the static exciton–exciton dipole interaction energy.

The excitonic nonlinear optical responses due to exciton-phonon interactions in strongly coupled exciton-phonon systems are investigated theoretically. It is shown that the influence of exciton-phonon interactions on the nonlinear optical absorptions and Kerr nonlinear coefficients is significant as the signal field frequency detuning from the exciton frequency approaches to the optical phonon frequency. How to manipulate the nonlinear optical responses by using the control fields is also presented.

We study the behavior of the Rabi oscillations of a driven central spin (qubit) coupled to an antiferromagnetic spin bath (environment). It is found that the decoherence behavior of the central spin depends on the detuning, driving strength, the qubit-bath coupling and an important factor, associated with the number of the coupled atoms, the detailed lattice structure, and the temperature of the environment. If the detuning exists, the Rabi oscillations may show the behavior of collapses and revivals; however, if the detuning is zero, such a behavior will not appear. We investigate the weighted frequency distribution of the time evolution of the central spin inversion and give this phenomenon of collapses and revivals a reasonable explanation. We also discuss the decoherence and the pointer states of the qubit from the perspectives of the von Neumann entropy. It is found that the eigenstates of the qubit self-Hamiltonian emerge as the pointer states in the weak system-environment coupling limit., Accepted for publication in New Journal of Physics (19 pages, 4 figures)

Using the spin-wave approximation, we study the geometric phase (GP) of a central spin (signal qubit) coupled to an antiferromagnetic (AF) environment under the application of an external global magnetic field. The external magnetic field affects the GP of the qubit directly and also indirectly through its effect on the AF environment. We find that when the applied magnetic field is increased to the critical magnetic field point, the AF environment undergoes a spin-flop transition, a first-order phase transition, and at the same time the GP of the qubit changes abruptly to zero. This sensitive change of the GP of a signal qubit to the parameter change of a many-body environment near its critical point may serve as another efficient tool or witness to study the many-body phase transition. The influences of the AF environment temperature and crystal anisotropy field on the GP are also investigated., Comment: 5 figures; Phys. Rev. A (in press)

In this letter we have studied the effect of image potential on the ground state energy of a shallow donor impurity near a sharp surface of a semi-infinite crystal. The energy expression of the system as a function of its position is calculated with the variational method. The results are discussed.

We propose a scheme that allows generation of the Bell and $W$-type entangled states of excitons in quantum dots confined in a single-mode microcavity. It is shown that the entanglement of excitons can be generated when the photons leaking out of the cavity are detected by photon counter. The effect of environmental temperature on the entanglement of excitonic states is also studied.

Using the spin wave approximation, we study the decoherence dynamics of a central spin coupled to an antiferromagnetic environment under the application of an external global magnetic field. The external magnetic field affects the decoherence process through its effect on the antiferromagnetic environment. It is shown explicitly that the decoherence factor which displays a Gaussian decay with time depends on the strength of the external magnetic field and the crystal anisotropy field in the antiferromagnetic environment. When the values of the external magnetic field is increased to the critical field point at which the spin-flop transition (a first-order quantum phase transition) happens in the antiferromagnetic environment, the decoherence of the central spin reaches its highest point. This result is consistent with several recent quantum phase transition witness studies. The influences of the environmental temperature on the decoherence behavior of the central spin are also investigated., 29 preprint pages, 4 figures, to appear in New Journal of Physics

The exact quantum dynamics of the reduced density matrix of two coupled spin qubits in a quantum Heisenberg XY spin star environment in the thermodynamic limit at arbitrarily finite temperatures is obtained using a novel operator technique. In this approach, the transformed Hamiltonian becomes effectively Jaynes-Cumming like and thus the analysis is also relevant to cavity quantum electrodynamics. This special operator technique is mathematically simple and physically clear, and allows us to treat systems and environments that could all be strongly coupled mutually and internally. To study their entanglement evolution, the concurrence of the reduced density matrix of the two coupled central spins is also obtained exactly. It is shown that the dynamics of the entanglement depends on the initial state of the system and the coupling strength between the two coupled central spins, the thermal temperature of the spin environment and the interaction between the constituents of the spin environment. We also investigate the effect of detuning which in our model can be controlled by the strength of a locally applied external magnetic field. It is found that the detuning has a significant effect on the entanglement generation between the two spin qubits., 9 pages (two-coulumn), 6 figures. To appear in Phys. Rev. B

The Berry phase of two coupled quantum dots is investigated. The coupled quantum dots are embedded in a high-$Q$ single mode cavity and coupled to the common phonon fields. We show how the Berry phase depends on the environmental temperatures.

The excitonic dynamics in a single quantum dot within a microcavity is investigated theoretically in terms of the perturbation treatment based on a unitary transformation. The excitonic Rabi oscillations with a damping rate are obtained explicitly. It is shown that the damping rate depends on exciton-phonon coupling constant and the vacuum Rabi frequency. Even at absolute zero temperature and in the vacuum cavity, the exciton-phonon interaction and exciton-photon interaction still cause excitonic decoherence. We also predict that under strong control fields the collapse and revival of excitonic Rabi oscillation may be observed for the quantum dots with small exciton-phonon coupling in the $T\ensuremath{\rightarrow}0$ limit.

The dynamics of charge qubit in a double quantum dot coupled to phonons is investigated theoretically in terms of a perturbation treatment based on a unitary transformation. The dynamical tunneling current is obtained explicitly. The result is compared with the standard perturbation theory at Born-Markov approximation. The decoherence induced by acoustic phonons is analyzed at length. It is shown that the contribution from deformation potential coupling is comparable to that from piezoelectric coupling in small dot size and large tunneling rate case. A possible decoupling mechanism is predicted., Comment: 8 pages, 6 figures

We propose a scheme to demonstrate the electromagnetically induced transparency (EIT) in a system of a superconducting Cooper-pair box coupled to a nanomechanical resonator. In this scheme, the nanomechanical resonator plays an important role to contribute additional auxiliary energy levels to the Cooper-pair box so that the EIT phenomenon could be realized in such a system. We call it here resonator-assisted induced transparency (RAIT). This RAIT technique provides a detection scheme in a real experiment to measure physical properties, such as the vibration frequency and the decay rate, of the coupled nanomechanical resonator., To appear in New Journal of Physics: Special Issue "Mechanical Systems at the Quantum Limit"

We report the results of a variational calculation for the ground state of a near-surface hydrogenic donor interacting with both surface and bulk longitudinal-optical (SO and BO) phonons in polar crystals. In calculation we also consider the effect of the image potentials. The variations of ground-state energies and binding energies with the depth R from the crystal surface are given for some materials. The results are discussed.