单光子量子路由的耗散影响

单光子量子路由对于在芯片中实现量子信息交换具有重大意义。研究单光子量子路由中的耗散影响能够更加真实的模拟实际实验的结果。研究发现耗散能级的存在使得同等条件下的量子路由概率减小,并且需要相对较强的耦合才能取得最大量子路由概率。同时,也建立了共振条件下量子路由概率同耦合强度以及耗散强度间的关系。     

Stark-Chirped Rapid Adiabatic Passage in Presence of Dissipation for Quantum Computation

Stark-chirped rapid adiabatic passage （SCRAP） is an important technique used for coherent quantum controls. In this paper we investigate how the practically-existing dissipation of the system influences on the efficiency of the passage, and thus the fidelities of the SCRAP-based quantum gates. With flux-biased Josephson qubits as a specifical example, our results show clearly that the efficiency of the logic gates implemented by SCRAP are robust against the weak dissipation. The influence due to the non-adiabtic transitions between the adiabatic passages is comparatively significantly small. Therefore, the SCRAP-based logic gates should be feasible for the realistic physical systems with noises.     

Brownian Motion of the Quantum Dissipation in the RWA

A microscopic approach treating the quantum dissipation process presented by Sun and Yu (Phys. Rev. A49 (1994) 592; A51 (1995) 1845) is invoked to construct the wavefunction of the composite system——the model for a harmonic oscillator interacting with a many-oscillator bath under the rotating wave approximation. It shows the back-action of the system on the bath. In particular, the dynamic evolution of the wavefunction for the composite system maintains a factorized form in its wavefunction. In the limited temperature, the reduced density matrix for the system is also calculated to clarify the influence of Brownian motion on the system.     

Quantum Thermal Amplifiers with Engineered Dissipation

A three-terminal device, able to control the heat currents flowing through it, is known as a quantum thermal transistor whenever it amplifies two output currents as a response to the external source acting on its third terminal. Several efforts have been proposed in the direction of addressing different engineering options of the configuration of the system. Here, we adhere to the scheme in which such a device is implemented as a three-qubit system that interacts with three separate thermal baths. However, another interesting direction is how to engineer the thermal reservoirs to magnify the current amplification. Here, we derive a quantum dynamical equation for the evolution of the system to study the role of distinct dissipative thermal noises. We compare the amplification gain in different configurations and analyze the role of the correlations in a system exhibiting the thermal transistor effect, via measures borrowed from the quantum information theory.     

Geometric Quantum Computing and Dissipation Models

Based on a simple periodical external field model, we investigate the impact of standard Leggett's dissipation on the Berry's phase, which is necessary for any practical implementation of geometric phase gate. It is found that the environmental noise, including the thermal and vacuum parts, could lead to a decaying term in the matrix of Berry's phase, which corresponds to the decoherence process of a qubit as a function of both time and temperature. A new type of two-level-system reservoir is also discussed, it is shown that the decaying term only depends on time, but not on temperature. A concrete case is exhibited by using the 1D Ohmic function.     

Dissipation and Decoherence in a Quantum Oscillator

The time development of the reduced density matrix for a quantum oscillator damped by coupling it to an ohmic environment is calculated via an identity of the Debye-Waller form. Results obtained some years ago by Hakim and the author in the free-particle limit⁽¹⁰⁾ are thus recovered. The evolution of a free particle in a prepared initial state is examined, and a previously published exchange^(5,9) is illuminated with figures showing no decoherence without dissipation. PACS number: 03.75.Ss     

Dissipation and quantum transport simulations in nanoscale devices

A key simulation issue is the development of a dissipation formalism for the time dependent density operator equation, that is amenable to numerical methods and incorporates the role of the environment on state renormalization and dissipation. Using standard super-operator calculus, projection operators, and separating the system of interest from the reservoir, the relevant operator equation is derived. In addition, the role of the reservoir on renormalizing the energy spectrum is discussed.     

量子耗散微扰方法的适用性

将微扰量子耗散理论得出的两态线性吸收光谱与严格结果相比较. 所考虑的近似理论为两套完备两阶量子耗散方程,其一为标准的编时微扰方法,另一为所谓的完备二阶驱动耗散耦合方程. 对于两态线性吸收光谱,可以得到解析解,将结果与严格公式比较,来评估这两种方法的适用性和应用范围.     

基于级联方程的量子耗散半经典方法

We present a semiclassical (SC) approach for quantum dissipative dynamics, constructed on basis of the hierarchical-equation-of-motion (HEOM) formalism. The dynamical components considered in the developed SC-HEOM are wavepackets'' phase-space moments of not only the primary reduced system density operator but also the auxiliary density operators (ADOs) of HEOM. It is a highly numerically efficient method, meanwhile taking into account the high-order effects of system-bath couplings. The SC-HEOM methodology is exemplified in this work on the hierarchical quantum master equation[J. Chem. Phys. 131, 214111 (2009)] and numerically demonstrated on linear spectra of anharmonic oscillators.     

Normal Ordering Solution to Quantum Dissipation and Its Induced Decoherence

We implement the normal ordering technique to study the quantum dissipation of a single mode harmonic oscillator system. The dynamic evolution of the system is investigated for a reasonable initial state by solving the Schrödinger equation directly through the normal ordering technique. The decoherence process of the system for the cases T=0 K and T≠0 K is investigated as an application.     

Direct Observation of Dissipation in Dynamical Search Algorithm using Transmon Qubits

Following recent work [Fortschritte der Physik 66, 1700080 (2018)], the dissipation effect of the dynamical quantum search algorithm (DQSA) is investigated. Such an algorithm is realized with the interaction of multi superconducting transmon qubits inside a 3D bus cavity. The dissipation of such system is caused by managing the sensitivity to charge noise via tuning the qubit frequency by employing Josephson energy. The probabilities of marked and unmarked states for the present algorithm have been calculated analytically and numerically. Such probabilities of marked states are sensitive to any change in the dissipation parameter. A deficiency causes the dissipation for the marked states, and that deficiency is added to the unmarked states. It is interesting to mention that one of the datasets at large dissipation rates gives an observation of the marked states probabilities which is related to the decoherence free subspace. It is predicted that the algorithm can be successfully implemented in the current experiments.     

Quantum State Transfer in Engineered Spin Chain under Influence of Spatially Distributed Environment

It has been shown that a quantum state could be perfectly transferred via a spin chain with engineered ＂always-on interaction＂. In this paper, we study a more realistic problem for such a quantum state transfer （QST） protocol, how the efficacy of QST is reduced by the quantum decoherence induced by a spatially distributed environment. Here, the environment is universally modeled as a bath of fermions located in different positions. By making use of the irreducible tensor method in angular momentum theory, we investigate the effect of environment on the efficiency of QST for both cases at zero and finite temperatures. We not only show the generic exponential decay of QST efficiency as the number of sites increase, but also find some counterintuitive effect, the QST can be enhanced as temperature increases in some cases.     

Quantum Secure Dialogue with Quantum Encryption

How to solve the information leakage problem has become the research focus of quantum dialogue. In this paper, in order to overcome the information leakage problem in quantum dialogue, a novel approach for sharing the initial quantum state privately between communicators, i.e., quantum encryption sharing, is proposed by utilizing the idea of quantum encryption. The proposed protocol uses EPR pairs as the private quantum key to encrypt and decrypt the traveling photons, which can be repeatedly used after rotation. Due to quantum encryption sharing, the public announcement on the state of the initial quantum state is omitted, thus the information leakage problem is overcome.The information-theoretical efficiency of the proposed protocol is nearly 100%, much higher than previous information leakage resistant quantum dialogue protocols. Moreover, the proposed protocol only needs single-photon measurements and nearly uses single photons as quantum resource so that it is convenient to implement in practice.     

Quantum State Transfer in Engineered Spin Chain under Influence of Spatially Distributed Environment

It has been shown that a quantum state could be perfectly transferred via a spin chain with engineered ``always-on interaction". In this paper, we study a more realistic problem for such a quantum state transfer (QST) protocol, how the efficacy of QST is reduced by the quantum decoherence induced by a spatially distributed environment. Here, the environment is universally modeled as a bath of fermions located in different positions. By making use of the irreducible tensor method in angular momentum theory, we investigate the effect of environment on the efficiency of QST for both cases at zero and finite temperatures. We not onlyshow the generic exponential decay of QST efficiency as the number of sites increase, but also find some counterintuitive effect, the QST can be enhanced as temperature increases in some cases.     

Quantum Secure Dialogue with Quantum Encryption

How to solve the information leakage problem has become the research focus of quantum dialogue. In this paper, in order to overcome the information leakage problem in quantum dialogue, a novel approach for sharing the initial quantum state privately between communicators, i.e., quantum encryption sharing, is proposed by utilizing the idea of quantum encryption. The proposed protocol uses EPR pairs as the private quantum key to encrypt and decrypt the traveling photons, which can be repeatedly used after rotation. Due to quantum encryption sharing, the public announcement on the state of the initial quantum state is omitted, thus the information leakage problem is overcome. The information-theoretical efficiency of the proposed protocol is nearly 100%, much higher than previous information leakage resistant quantum dialogue protocols. Moreover, the proposed protocol only needs single-photon measurements and nearly uses single photons as quantum resource so that it is convenient to implement in practice.     

Towards Quantum Control with Advanced Quantum Computing: A Perspective

We propose the combination of digital quantum simulation and variational quantum algorithms as an alternative approach to numerical methods for solving quantum control problems. As a hybrid quantum–classical framework, it provides an efficient simulation of quantum dynamics compared to classical algorithms, exploiting the previous achievements in digital quantum simulation. We analyze the trainability and the performance of such algorithms based on our preliminary works. We show that specific quantum control problems, e.g., finding the switching time for bang-bang control or the digital quantum annealing schedule, can already be studied in the noisy intermediate-scale quantum era. We foresee that these algorithms will contribute even more to quantum control of high precision if the hardware for experimental implementation is developed to the next level.