Decoupling Bang-Bang Group for Adiabatic Decoherence Control in a Three-Level Atom

In this paper, we study the control problem of adiabatic decoherence in a three-level atom. We will find thedecoupling bang-bang group for various configurations, including the V configuration and the cascade type of three-level atom subjected to adiabatic decoherence. We also give the programs to design a sequence of periodic twinborn pulses to suppress the decoherence.     

On Effectiveness of Protocol Creating Maximum Entanglement of Two Charge-Phase Qubits by Cavity Field

We revisit the protocols to create maximally entangled states between two Josephson junction （33） charge phase qubits coupled to a microwave field in a cavity as a quantum data bus. We analyze a novel mechanism of quantum decoherence due to the adiabatic entanglement between qubits and the data bus, the off-resonance microwave field. We show that even if the variable of the data bus can be adiabatically eliminated, the entanglement between the qubits and data bus remains and can decohere the superposition of two-particle state. Fortunately we can construct a decoherencefree subspace of two-dimension to against this adiabatic decoherence. To carry out the analytic study for this decoherence problem, we develop Frohlich transformation to re-derive the effective Hamiltonian of these systems, which is equivalent to that obtained from the adiabatic elimination approach.     

Holonomic quantum computation in the presence of decoherence

We present a scheme to study non-Abelian adiabatic holonomies for open Markovian systems. As an application of our framework, we analyze the robustness of holonomic quantum computation against decoherence. We pinpoint the sources of error that must be corrected to achieve a geometric implementation of quantum computation completely resilient to Markovian decoherence.     

Adiabatic quantum computation in open systems

We analyze the performance of adiabatic quantum computation (AQC) subject to decoherence. To this end, we introduce an inherently open-systems approach, based on a recent generalization of the adiabatic approximation. In contrast to closed systems, we show that a system may initially be in an adiabatic regime, but then undergo a transition to a regime where adiabaticity breaks down. As a consequence, the success of AQC depends sensitively on the competition between various pertinent rates, giving rise to optimality criteria.     

The Influence of Non‐Markovian Characters on Quantum Adiabatic Evolution

The influence of non‐Markovian characters on the adiabatic evolution is investigated. The adiabatic Raman process is simulated in a three‐level system coupled to two independent environments. The results show that the memory effect of environments can restrain the decoherence effect of the system. Even if the system has strong decay rates in the non‐Markovian environments, the adiabatic population transfer can be still completed efficiently. Moreover, the memory effect can reduce the dependence of the adiabatic evolution on the Rabi frequency. Specifically, the two independent non‐Markovian baths can suppress the decoherence more effectively than a single non‐Markovian bath.     

Localization of a macroscopic object induced by the factorization of internal adiabatic motion

To account for the phenomenon of quantum decoherence of a macroscopic object, such as the localization and disappearance of interference, we invoke the adiabatic quantum entanglement between its collective states (such as that of the center-of-mass (CM)) and its inner states based on our recent investigation. Under the adiabatic limit where motion of the CM does not excite the transition of inner states, it is shown that the wave function of the macroscopic object can be written as an entangled state with correlation between adiabatic inner states and quasi-classical motion configurations of the CM. Since the adiabatic inner states are factorized with respect to each component of the macroscopic object, this adiabatic separation can induce the quantum decoherence. This observation thus provides us with a possible solution to the Schr?dinger cat paradox. Received 24 October 2000 and Received in final form 8 March 2001     

Decoherence-free generation of many-particle entanglement by adiabatic ground-state transitions

We discuss a decoherence insensitive method to create many-particle entanglement in a spin system with controllable collective interactions and propose an implementation in an ion trap. An adiabatic change of parameters allows a transfer from separable to a large variety of entangled eigenstates. We show that the Hamiltonian can have a supersymmetry permitting an explicit construction of the ground state at all times. Of particular interest is a transition in a nondegenerate ground state with a finite energy gap since here the influence of collective as well as individual decoherence mechanisms is substantially reduced. A lower bound for the energy gap is given.     

Entangled atomic state generation via adiabatic evolution of dark eigenstates in cavity QED

We propose a scheme for generating a two-atom entangled state and an N-atom W state using adiabatic evolution of dark eigenstates in cavity QED. The time required to complete the process does not need precise control. Since the cavity modes are never excited during the operations by engineering adiabatic evolution and controlling the atom–cavity couplings, the decoherence of the cavity decay can be suppressed.     

分子磁体与环境的纠缠和退相干

本文研究了双轴分子磁体在耗散环境中的相干量子隧穿,作为环境的声子库抑制了相干量子隧穿,从而引起分子磁体中薛定谔猫态的退相干. 而环境内部声子之间的相互作用会导致分子磁体与热库之间退耦合,于是对退相干有一定的抑制作用. 在绝热近似和非绝热近似下,借助于约化密度矩阵计算了超Ohmo耗散中分子磁体与环境之间的纠缠度,当纠缠达到最大时,相干隧穿被完全抑制.     

Adiabatic quantum computing with phase modulated laser pulses

Implementation of quantum logical gates for multilevel systems is demonstrated through decoherence control under the quantum adiabatic method using simple phase modulated laser pulses. We make use of selective population inversion and Hamiltonian evolution with time to achieve such goals robustly instead of the standard unitary transformation language.     

Adiabatic cavity QED with pairs of atoms

We study the dynamics of a pair of atoms, resonantly interacting with a single mode cavity, in the situation where the atoms enter the cavity with a time delay between them. Using time dependent coupling functions to represent the spatial profile of the mode, we considered the adiabatic limit of the system. Although the time evolution is mostly adiabatic, energy crossings play an important role in the system dynamics. Following from this, entanglement, and a procedure for cavity state teleportation are considered. We examine the behaviour of the system when we introduce decoherence, a finite detuning, and potential asymmetries in the coupling profiles of the atoms.     

Spin-1/2 geometric phase driven by decohering quantum fields

We calculate the geometric phase of a spin-1/2 system driven by one and two mode quantum fields subject to decoherence. Using the quantum jump approach, we show that the corrections to the phase in the no-jump trajectory are different when considering adiabatic and nonadiabatic evolutions. We discuss the implications of our results from both fundamental as well as quantum computational perspectives.     

Experimental implementation of an adiabatic quantum optimization algorithm

We report the realization of a nuclear magnetic resonance computer with three quantum bits that simulates an adiabatic quantum optimization algorithm. Adiabatic quantum algorithms offer new insight into how quantum resources can be used to solve hard problems. This experiment uses a particularly well-suited three quantum bit molecule and was made possible by introducing a technique that encodes general instances of the given optimization problem into an easily applicable Hamiltonian. Our results indicate an optimal run time of the adiabatic algorithm that agrees well with the prediction of a simple decoherence model.     

通过绝热过程实现任意一原子态的隐形传态(英文)

我们利用腔场和激光相互作用,提出一个冗余的、对消相干不敏感的方案,来传输任意一个三能级原子的态.由于原子自发跃迁和腔延迟作用会造成信息丢失,通过用部分绝热过程和适当的原子场耦合的设计,信息丢失能够被有效的抑制,此方案传送成功的几率是0.5,保真度是1.     

Geometric phase gate with trapped ions in thermal motion by adiabatic passage

We propose a scheme for implementing two-qubit geometric phase gate via the adiabatic evolution for trapped ions in thermal motion, leveraging on the stimulated Raman adiabatic passage with the geometric phase mechanism. Evolution along a dark state makes our scheme not only immune from decoherence due to spontaneous emission from excited states, but also rid off the dynamical phase. Furthermore, due to the opposite detuning of the driving lasers, the vibrational states of the trapped ions are only virtually excited during the operations, so our scheme is also insensitive to the occupation number of the vibrational mode.     

Realization of adiabatic and diabatic CZ gates in superconducting qubits coupled with a tunable coupler

High fidelity two-qubit gates are fundamental for scaling up the superconducting qubit number.We use two qubits coupled via a frequency-tunable coupler which can adjust the coupling strength,and demonstrate the CZ gate using two different schemes,adiabatic and diabatic methods.The Clifford based randomized benchmarking(RB) method is used to assess and optimize the CZ gate fidelity.The fidelities of adiabatic and diabatic CZ gates are 99.53(8)% and 98.72(2)%,respectively.We also analyze the errors induced by the decoherence.Comparing to 30 ns duration time of adiabatic CZ gate,the duration time of diabatic CZ gate is 19 ns,revealing lower incoherence error rate r'_(incoherent,int)=0.0197(5) compared to r_(incoherent,int)=0.0223(3).     

Nonadiabatic corrections to a quantum dot quantum computer working in adiabatic limit

The time of operation of an adiabatic quantum computer must be less than the decoherence time, otherwise the computer would be nonoperative. So far, the nonadiabatic corrections to an adiabatic quantum computer are merely theoretical considerations. By the above reason, we consider the particular case of a quantum-dot-confined electron spin qubit working adiabatically in the nanoscale regime (e.g., in the MeV range of energies) and include nonadiabatic corrections in it. If the decoherence times of a quantum dot computer are ～100 ns [J M Kikkawa and D D Awschalom, Phys. Rev. Lett. 80, 4313 (1998)] then the predicted number of one qubit gate (primitive) operations of the Loss–DiVincenzo quantum computer in such an interval of time must be >10 ¹⁰. However, if the quantum-dot-confined electron spin qubit is very excited (i.e., the semiclassical limit) the number of operations of such a computer would be approximately the same as that of a classical computer. Our results suggest that for an adiabatic quantum computer to operate successfully within the decoherence times, it is necessary to take into account nonadiabatic corrections.     

Scalable Implementation of Multi-qubit Quantum Grover Search with Atomic Ensembles by Adiabatic Passage

We propose a simple scheme to implement multi-qubit quantum Grover search with atomic ensembles by adiabatic passage. The scheme is immune to the atomic spontaneous emission, cavity decay and fiber decay. Furthermore, the process can be speeded up with atomic ensemble instead of single atom, which is important in view of decoherence. With each atomic ensemble confined in an individual cavity, our scheme is experimentally scalable to multi-qubit cases.     

Generation of Wn state with three atoms trapped in two remote cavities coupled by an optical fibre

We propose two schemes for the generation of the Wn state with three atoms separately trapped in two distant cavities coupled by an optical fibre.One is implemented by controlling the interaction time,the other is implemented via the adiabatic passage.The influence of various decoherence processes,such as spontaneous emission of the atoms and photon leakages of the cavities and the optical fibre,on the fidelity is also investigated.It is found that the Wn state can be generated with high fidelity even when these decoherence processes are present.