High entanglement generation and high fidelity quantum state transfer in a non-Markovian environment

This paper analyses a system of two independent qubits off-resonantly coupled to a common non-Maxkovian reservoir at zero temperature. Compared with the results in Markovian reservoirs, we find that much higher values of entanglement can be obtained for an initially factorized state of the two-qubit system. The maximal value of the entanglement increases as the detuning grows. Moreover, the entanglement induced by non-Maxkovian environments is more robust against the asymmetrical couplings between the two qubits and the reservoir. Based on this system, we also show that quantum state transfer can be implemented for arbitrary input states with high fidelity in the non-Markovian regime rather than the Markovian case in which only some particular input states can be successfully transferred.

Quantum state transfer between atomic ensembles trapped in separate cavities via adiabatic passage

We propose a new approach for quantum state transfer（QST） between atomic ensembles separately trapped in two distant cavities connected by an optical fiber via adiabatic passage. The three-level Λ-type atoms in each ensemble dispersively interact with the nonresonant classical field and cavity mode. By choosing appropriate parameters of the system, the effective Hamiltonian describes two atomic ensembles interacting with ＂the same cavity mode＂ and has a dark state. Consequently, the QST between atomic ensembles can be implemented via adiabatic passage. Numerical calculations show that the scheme is robust against moderate fluctuations of the experimental parameters. In addition, the effect of decoherence can be suppressed effectively. The idea provides a scalable way to an atomic-ensemble-based quantum network, which may be reachable with currently available technology.

High-dimensional quantum state transfer in a noisy network environment

We propose and analyze an efficient high-dimensional quantum state transfer protocol in an XX coupling spin network with a hypercube structure or chain structure. Under free spin wave approximation, unitary evolution results in a perfect high-dimensional quantum swap operation requiring neither external manipulation nor weak coupling. Evolution time is independent of either distance between registers or dimensions of sent states, which can improve the computational efficiency. In the low temperature regime and thermodynamic limit, the decoherence caused by a noisy environment is studied with a model of an antiferromagnetic spin bath coupled to quantum channels via an Ising-type interaction. It is found that while the decoherence reduces the fidelity of state transfer, increasing intra-channel coupling can strongly suppress such an effect. These observations demonstrate the robustness of the proposed scheme.

Long-distance quantum state transfer through cavity-assisted interaction

We propose a scheme for long-distance quantum state transfer between different atoms based on cavity-assisted interactions. In our scheme, a coherent optical pulse sequentially interacts with two distant atoms trapped in separated cavities. Through the measurement of the state of the first atom and the homodyne detection of the final output coherent light, the quantum state can be transferred into the second atom with a success probability of unity and a fidelity of unity. In addition, our scheme neither requires the high-Q cavity working in the strong coupling regime nor employs the single-photon quantum channel, which greatly relaxes the experimental requirements.

Enhancement of multiatom non-classical correlations and quantum state transfer in atom–cavity–fiber system

Taking the advantage of "parity kicks" pulses, we investigate the non-classical correlation dynamics and quantum state transfer in an atom–cavity–fiber system, which consists of two identical subsystems, each subsystem comprising of multiple two-level atoms trapped in two remote single-model optical cavities that are linked by an optical fiber. It is found that the non-classical correlations and the fidelity of quantum state transfer(between the atoms) can be greatly improved by the parity kicks pulses. In particular, with decrease of the time intervals between two consecutive pulses, perfect non-classical correlation transfer and entangled state transfer can be achieved.

Fast achievement of quantum state transfer and distributed quantum entanglement by dressed states

We propose schemes to realize quantum state transfer and prepare quantum entanglement in coupled cavity and cavity-fiber-cavity systems,respectively,by using the dressed state method.We first give the expression of pulses shape by using dressed states and then find a group of Gaussian pulses that are easy to realize in experiment to replace the ideal pulses by curve fitting.We also study the influence of some parameters fluctuation,atomic spontaneous emission,and photon leakage on fidelity.The results show that our schemes have good robustness.Because the atoms are trapped in different cavities,it is easy to perform different operations on different atoms.The proposed schemes have the potential applications in dressed states for distributed quantum information processing tasks.

Quantum State Transfer among Three Ring-Connected Atoms

A robust quantum state transfer scheme is discussed for three atoms that are trapped by separated cavities linked via optical fibers in a ring connection. It is shown that, under the effective three-atom Ising model, an arbitrary unknown quantum state can be transferred from one atom to another deterministically via an auxiliary atom with maximum unit fidelity. The only required operation for this scheme is replicating turning on/off the local laser fields applied to the atoms for two steps with time cost √2π/Γ0. The scheme is insensitive to cavity leakage and atomic position due to the condition Δ≈κ》g. Another advantage of this scheme is that the cooperative influence of spontaneous emission and operating time error can reduce the time cost for maximum fidelity and thus can speed up the implementation of quantum state transfer.

Quantum state transfer via a hybrid solid–optomechanical interface

We propose a scheme to implement quantum state transfer between two distant quantum nodes via a hybrid solid–optomechanical interface. The quantum state is encoded on the native superconducting qubit, and transferred to the microwave photon, then the optical photon successively, which afterwards is transmitted to the remote node by cavity leaking,and finally the quantum state is transferred to the remote superconducting qubit. The high efficiency of the state transfer is achieved by controllable Gaussian pulses sequence and numerically demonstrated with theoretically feasible parameters.Our scheme has the potential to implement unified quantum computing–communication–computing, and high fidelity of the microwave–optics–microwave transfer process of the quantum state.

Quantum State Transfer between a Mechanical Oscillator and a Distant Moving Atom

We propose a scheme for high fidelity quantum state transfer from a mechanical oscillator to a distant moving atom. In the scheme, two optical cavities connected by an optical fiber are interacted effectively through adiabatically eliminating fiber mode under large detuning limit. The quantum state transfer fidelity can be raised asymptotically to 100% by optimizing the Gaussian pulse G(t), the maximum atom-cavity coupling strength Ωmax, and the atomic velocity v. We also show that the affect of dissipation can be obviously depressed by synchronously increasing Ωmax and v.

Quantum state transfer via adiabatic passage

Based on adiabatic passage, we propose a scheme for implementing the quantum transfer of an unknown atomic state. In our scheme, we utilize photons for ideal quantum transmission between two cavities with the successful probability being about 1. Meanwhile, the scheme is robust against the effects of atomic spontaneous emission. It may be useful for transferring quantum information among spatially distant atoms.

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 theirreducible tensor method in angular momentum theory,we investigate the effect of environment on the efficiency of QSTfor both cases at zero and finite temperatures.We not only show the generic exponential decay of QST efficiency as thenumber of sites increase,but also find some counterintuitive effect,the QST can be enhanced as temperature increasesin some cases.

Deterministic Generation of Quantum State Transfer Between Spatially Separated Single Molecule Magnets

We propose a new scheme for realizing deterministic quantum state transfer (QST) between two spatiallyseparated single molecule magnets (SMMs) with the framework of cavity quantum electrodynamics (QED).In the presentscheme,two SMMs are trapped in two spatially separated optical cavities coupled by an optical fiber.Through strictlynumerically simulating,we demonstrate that our scheme is robust with respect to the SMMs' spontaneous decay andfiber loss under the conditions of dispersive SMMs-field interaction and strong coupling of cavity fiber.In addition,wealso discuss the influence of photon leakage out of cavities and show that our proposal is good enough to demonstrate thegeneration of QST with high fidelity utilizing the current experimental technology.The present investigation providesresearch opportunities for realizing QST between solid-state qubits and may result in a substantial impact on the progressof solid-state-based quantum communications network.

Three-Dimensional Quantum State Transferring Between Two Remote Atoms by Adiabatic Passage under Dissipation

Recently,Zhou et al.[Phys.Rev.A 79 (2009) 044304] proposed a scheme for transferring three-dimensionalquantum states between remote atomic qubits confined in cavities connected by fibers through adiabatic passage.Inorder to avoid the decoherence due to spontaneous emission,Zhou et ad.utilized the large detuning atom-field interaction.In the present paper,we discuss the influence of dissipation on the scheme in both the resonant atom-field interactioncase and the large detuning case.We numerically analyze the success probability and the transferring fidelity.It is shownthat the resonant case is a preferable choice for the technique of the stimulated Raman adiabatic passage (STIRAP) dueto the shorter operation time and the smaller probability of dissipation.

Robust beam splitter with fast quantum state transfer through a topological interface

The Su–Schrieffer–Heeger(SSH)model,commonly used for robust state transfers through topologically protected edge pumping,has been generalized and exploited to engineer diverse functional quantum devices.Here,we propose to realize a fast topological beam splitter based on a generalized SSH model by accelerating the quantum state transfer(QST)process essentially limited by adiabatic requirements.The scheme involves delicate orchestration of the instantaneous energy spectrum through exponential modulation of nearest neighbor coupling strengths and onsite energies,yielding a significantly accelerated beam splitting process.Due to properties of topological pumping and accelerated QST,the beam splitter exhibits strong robustness against parameter disorders and losses of system.In addition,the model demonstrates good scalability and can be extended to two-dimensional crossed-chain structures to realize a topological router with variable numbers of output ports.Our work provides practical prospects for fast and robust topological QST in feasible quantum devices in large-scale quantum information processing.

Two-band model as a quantum data bus for quantum state transfer

We study the dynamics of an electron spin state transfer along a half-filled two-band model(TBM).It is shown that this solvable and realistic medium has an energy gap between the ground and first-excited states in the half-filled case.By connecting two qubits to two sites of the TBM,the system can accomplish a high-fidelity and long-distance quantum state transfer(QST).Moreover,numerical simulations have been performed for a finite system.The results show that the numerical and analytical results of the effective coupling strength agree well with each other.Furthermore,the investigation shows that the reduced density matrix also has high fidelity beyond the range of perturbation.

Fast and perfect state transfer in superconducting circuit with tunable coupler

In quantum computation and quantum information processing, the manipulation and engineering of quantum systems to suit certain purposes are an ongoing task. One such example is quantum state transfer(QST), an essential requirement for both quantum communication and large-scale quantum computation. Here we engineer a chain of four superconducting qubits with tunable couplers to realize the perfect state transfer(PST) protocol originally proposed in quantum spin networks and successfully demonstrate the efficient transfer of an arbitrary single-qubit state from one end of the chain to the other,achieving a high fidelity of 0.986 in just 25 ns. This demonstrated QST is readily to extend to larger chain and multi-node configurations, thus serving as a desirable tool for scalable quantum information processing.

State transfer and entanglement between two-and four-level atoms in a cavity

Qudits with a large Hilbert space to host quantum information are widely utilized in various applications, such as quantum simulation and quantum computation, but the manipulation and scalability of qudits still face challenges. Here, we propose a scheme to directly and locally transfer quantum information from multiple atomic qubits to a single qudit and vice versa in an optical cavity. With the qubit–qudit interaction induced by the cavity, our scheme can transfer quantum states efficiently and measurement-independently. In addition, this scheme can robustly generate a high-dimensional maximal entangled state with asymmetric particle numbers, showing its potential in realizing an entanglement channel. Such an information interface for qubits and qudit may have enlightening significance for future research on quantum systems in hybrid dimensions.

High-fidelity quantum state transfer through a dissipative quantum data bus

We propose and analyze a robust quantum state transfer protocol through a scalable quantum data bus that consists of a network of controlled dissipative modules.In particular,we first demonstrate the ability to achieve perfect state transfer between two distinct quantum sites which are adiabatically coupled to the data bus in non-dissipative situation.We then consider the role of dissipation in adiabatic quantum state transfer via using Born–Markov master equation in the standard Lindblad form.Numerical simulation shows that the dissipation effect on the quality of transmission can be suppressed by engineering the network couplings of data bus properly.

Long-range adiabatic quantum state transfer through a linear array of quantum dots

We introduce an adiabatic long-range quantum communication proposal based on a quantum dot array.By adiabatically varying the external gate voltage applied on the system,the quantum information encoded in the electron can be transported from one end dot to another.We numerically solve the schr dinger equation for a system with a given number of quantum dots.It is shown that this scheme is a simple and efficient protocol to coherently manipulate the population transfer under suitable gate pulses.The dependence of the energy gap and the transfer time on system parameters is analyzed and shown numerically.We also investigate the adiabatic passage in a more realistic system in the presence of inevitable fabrication imperfections.This method provides guidance for future realizations of adiabatic quantum state transfer in experiments.