Quantum State Transfer Research Articles

A game of quantum catch.

Quantum Optics Realization of a quantum communication network or quantum internet will depend on the ability to successfully transfer quantum states between nodes of the network. Photons are expected to be the carriers of that information, but scattering losses and a mismatch between sender and

Robust quantum state transfer inspired by Dzyaloshinskii-Moriya interactions

Quantum state transfer (QST) is a fundamental problem in quantum mechanics and is important for quantum information processing. In this paper we explore a fast, robust, and efficient QST in spin-based quantum dots. Differing from the usual method that only uses the exchange interactions to control the evolution of the spin system, here we treat the non-negligible Dzyaloshinskii-Moriya (DM) interactions that can be electrically and thermally controlled in quantum dots as an assisted driving to accelerate the population transfer. We demonstrate that the DM interactions are not an error source, but are beneficial for population evolution under certain condition because they can sufficiently eliminate the undesirable quantum transitions among adiabatic passages and strictly maintain the population evolution in a designed passage with high efficiency. We give a generic $N$-spin anisotropic Heisenberg spin model to describe the population evolution and take specific two- and three-spin systems as examples to demonstrate the advantages of the DM interactions for QST.

Guest Editorial – Special Issue on Quantum Circuits

Guest Editorial – Special Issue on Quantum Circuits

Multi-path photon-phonon converter in optomechanical system at single-quantum level.

Based on photon-phonon nonlinear interaction, a scheme of controllable photon-phonon converters is proposed at single-quantum level in a composed quadratically coupled optomechanical system. With the assistance of the mechanical oscillator, the Kerr nonlinear effect between photon and phonon is enhanced so that the single-photon state can be converted into the phonon state with high fidelity even under the current experimental condition that the single-photon coupling rate is much smaller than mechanical frequency (g ≪ ωm). The state transfer protocols and their transfer fidelity are discussed analytically and numerically. A multi-path photon-phonon converter is designed by combining the optomechanical system with low frequency resonators, which can be controlled by experimentally adjustable parameters. This work provides us a potential platform for quantum state transfer and quantum information.

Second-order magnetic field gradient-induced strong coupling between nitrogen-vacancy centers and a mechanical oscillator

We consider a cantilever mechanical oscillator(MO) made of diamond. There is a nitrogen-vacancy(NV) center at the end of the cantilever. Two magnetic tips induce strong second order magnetic field gradient near the NV center. Under a coherent driving on MO, we find that the coupling between the MO and the NV center can be greatly enhanced. We studied how to realize quantum state transfer between MO and NV center and generate entanglement between them. We also proposed a scheme to generate the two-mode squeezing between different MO modes by coupling them to the same NV center. The decoherence and dissipation effects for both MO and NV center are numerically calculated by taking the present experimental parameters. It is found that high fidelity quantum state transfer, entanglement generation, and large two-mode squeezing could be achieved.

Realization of a Cascaded Quantum System: Heralded Absorption of a Single Photon Qubit by a Single-Electron Charged Quantum Dot.

Photonic losses pose a major limitation for the implementation of a quantum state transfer between nodes of a quantum network. A measurement that heralds a successful transfer without revealing any information about the qubit may alleviate this limitation. Here, we demonstrate the heralded absorption of a single photonic qubit, generated by a single neutral quantum dot, by a single-electron charged quantum dot that is located 5m away. The transfer of quantum information to the spin degree of freedom takes place upon the emission of a photon; for a properly chosen or prepared quantum dot, the detection of this photon yields no information about the qubit. We show that this process can be combined with local operations optically performed on the destination node by measuring classical correlations between the absorbed photon color and the final state of the electron spin. Our work suggests alternative avenues for the realization of quantum information protocols based on cascaded quantum systems.

Robust quantum entanglement generation and generation-plus-storage protocols with spin chains

Reliable quantum communication/processing links between modules are a necessary building block for various quantum processing architectures. Here we consider a spin chain system with alternating strength couplings and containing three defects, that impose three domain walls between topologically distinct regions of the chain. We show that -- in addition to its useful, high fidelity, quantum state transfer properties -- an entangling protocol can be implemented in this system, with optional localisation and storage of the entangled states. We demonstrate both numerically and analytically that, given a suitable initial product-state injection, the natural dynamics of the system produces a maximally entangled state at a given time. We present detailed investigations of the effects of fabrication errors, analyzing random static disorder both in the diagonal and off-diagonal terms of the system Hamiltonian. Our results show that the entangled state formation is very robust against perturbations of up to $\sim10\%$ the weaker chain coupling, and also robust against timing injection errors. We propose a further protocol which manipulates the chain in order to localise and store each of the entangled qubits. The engineering of a system with such characteristics would thus provide a useful device for quantum information processing tasks involving the creation and storage of entangled resources.

Coupling librational and translational motion of a levitated nanoparticle in an optical cavity

An optically levitated nonspherical nanoparticle can exhibit both librational and translational vibrations due to orientational and translational confinements of the optical tweezer, respectively. Usually, the frequency of its librational mode in a linearly-polarized optical tweezer is much larger than the frequency of its translational mode. Because of the frequency mismatch, the intrinsic coupling between librational and translational modes is very weak in vacuum. Here we propose a scheme to couple its librational and center-of-mass modes with an optical cavity mode. By adiabatically eliminating the cavity mode, the beam splitter Hamiltonian between librational and center-of-mass modes can be realized. We find that high-fidelity quantum state transfer between the librational and translational modes can be achieved with practical parameters. Our work may find applications in sympathetic cooling of multiple modes and quantum information processing.

Quantum speed limits for quantum-information-processing tasks

We derive algebraic bounds on achievable rates for quantum state transfer and entanglement generation in general quantum systems. We apply these bounds to graph-based models of local quantum spin systems to obtain speed limits on these tasks. A comparison to numerical optimal control results for spin chains suggests that unexplored regions of the dynamical landscape may support enhanced performance of key quantum information processing tasks.

Fast adiabatic quantum state transfer and entanglement generation between two atoms via dressed states

We propose a dressed-state scheme to achieve shortcuts to adiabaticity in atom-cavity quantum electrodynamics for speeding up adiabatic two-atom quantum state transfer and maximum entanglement generation. Compared with stimulated Raman adiabatic passage, the dressed-state scheme greatly shortens the operation time in a non-adiabatic way. By means of some numerical simulations, we determine the parameters which can guarantee the feasibility and efficiency both in theory and experiment. Besides, numerical simulations also show the scheme is robust against the variations in the parameters, atomic spontaneous emissions and the photon leakages from the cavity.

Rapid quantum state transfer based on bang–bang Lyapunov control under various dissipative modes

In quantum state transfer and tracking, fast control of quantum states are effective against the decoherence caused by external environment and information processing. The variational method and maximum principle are often used to solve the time-optimal control problems. However, analytic results cannot be obtained for many cases and it is necessary to find methods that can solve optimal control problems very efficiently. By comparing the advantages and disadvantages of the existing Lyapunov control and bang–bang control, we apply in this paper a new method that combines bang–bang control and Lyapunov control and can solve the time-optimal control problems in the open quantum system. Numerical simulations for a two-level open quantum system validate the effectiveness of the method. Furthermore, the optimized scheme avoids high frequency oscillation that occurs in bang–bang control.

Deterministic transfer of an unknown qutrit state assisted by the low-Q microwave resonators

Qutrits (i.e., three-level quantum systems) can be used to achieve many quantum information and communication tasks due to their large Hilbert spaces. In this work, we propose a scheme to transfer an unknown quantum state between two flux qutrits coupled to two superconducting coplanar waveguide resonators. The quantum state transfer can be deterministically achieved without measurements. Because resonator photons are virtually excited during the operation time, the decoherences caused by the resonator decay and the unwanted inter-resonator crosstalk are greatly suppressed. Moreover, our approach can be adapted to other solid-state qutrits coupled to circuit resonators. Numerical simulations show that the high-fidelity transfer of quantum state between the two qutrits is feasible with current circuit QED technology.

Intracity Quantum Communication via Thermal Microwave Networks

Communication over proven-secure quantum channels is potentially one of the most wide-ranging applications of currently developed quantum technologies. It is generally envisioned that in future quantum networks, separated nodes containing stationary solid-state or atomic qubits are connected via the exchange of optical photons over large distances. In this work we explore an intriguing alternative for quantum communication via all-microwave networks. To make this possible, we describe a general protocol for sending quantum states through thermal channels, even when the number of thermal photons in the channel is much larger than one. The protocol can be implemented with state-of-the-art superconducting circuits and enables the transfer of quantum states over distances of ~100 m via microwave transmission lines cooled to only T=4K. This opens up completely new possibilities for quantum communication within and across buildings, and consequently, for the implementation of intra-city quantum networks based on microwave technology only.

Quantum State Transfer via Noisy Photonic and Phononic Waveguides

We describe a quantum state transfer protocol, where a quantum state of photons stored in a first cavity can be faithfully transferred to a second distant cavity via an infinite 1D waveguide, while being immune to arbitrary noise (e.g., thermal noise) injected into the waveguide. We extend the model and protocol to a cavity QED setup, where atomic ensembles, or single atoms representing quantum memory, are coupled to a cavity mode. We present a detailed study of sensitivity to imperfections, and apply a quantum error correction protocol to account for random losses (or additions) of photons in the waveguide. Our numerical analysis is enabled by matrix product state techniques to simulate the complete quantum circuit, which we generalize to include thermal input fields. Our discussion applies both to photonic and phononic quantum networks.

Comparing the effects of atomic damping and velocity fluctuations upon transfer of quantum state in a bimodal cavity QED

In the present work we study the influence of both the fluctuation effects of the atom velocity and the atomic decay on the fidelity corresponding to a protocol for the quantum state transfer between two modes of a bimodal cavity QED. In our model the atom interacts separately with each mode, which is made possible by applying the Stark shift effect on the atomic-levels to tuning (detuning) properly modes A and B.

Multiple data access via a common cavity bus in circuit QED

SummaryAccessing multiple data through a common bus in quantum information processing is challenging. Experimental demonstration of quantum state transfer between a pair of superconducting phase qubit [M. A. Sillanpää et al., Nature 449, 438 (2007)] motivates us to construct a scheme for accessing and transferring multi‐qubit quantum information through a common cavity bus. Here, we have presented an efficient scheme to access multiple data through single channel using superconducting qubit and superconducting cavity resonator. The qubit–cavity photon coupling offers transfer of quantum data in different location of a quantum processing system from multiple users through a common superconducting cavity resonator. Instead of phase qubit, charge qubit is found to be more advantageous in qubit–cavity interaction for quantum data transformation, because charge qubit is immune to flux and external flux is used to select specific qubit from a set of qubits. The scheme is very generic and provides M‐output from N‐number of inputs via a common cavity in circuit quantum electrodynamics. The flexibility of the scheme allows us to implement multiplexer, demultiplexer, and so on for quantum data manipulation in a similar manner as in classical digital electronics. This scheme is useful to reduce the circuit complexity in quantum processor named as ‘quprocessor’. Copyright © 2017 John Wiley & Sons, Ltd.

Sublattice dynamics and quantum state transfer of doublons in two-dimensional lattices

We study the dynamics of two strongly-interacting fermions moving in 2D lattices under the action of a periodic electric field, both with and without a magnetic flux. Due to the interaction, these particles bind together forming a doublon. We derive an effective Hamiltonian that permits us to understand the interplay between the interaction and the driving, revealing surprising effects that constrain the movement of the doublons. We show that it is possible to confine doublons to just the edges of the lattice, and also to a particular sublattice, if different sites in the unit cell have different coordination numbers. Contrary to what happens in 1D systems, here we observe the coexistence of both topological and Shockley-like edge states when the system is in a non-trivial phase.

Perfect state transfer on graphs with a potential

In this paper we study quantum state transfer (also called quantum tunneling) on graphs when there is a potential function on the vertex set. We present two main results. First, we show that for paths of length greater than three, there is no potential on the vertices of the path for which perfect state transfer between the endpoints can occur. In particular, this answers a question raised by Godsil in Section 20 of [1]. Second, we show that if a graph has two vertices that share a common neighborhood, then there is a potential on the vertex set for which perfect state transfer will occur between those two vertices. This gives numerous examples where perfect state transfer does not occur without the potential, but adding a potential makes perfect state transfer possible. In addition, we investigate perfect state transfer on graph products, which gives further examples where perfect state transfer can occur.

Systematic Magnus-Based Approach for Suppressing Leakage and Nonadiabatic Errors in Quantum Dynamics

We present a systematic, perturbative method for correcting quantum gates to suppress errors that take the target system out of a chosen subspace. It addresses the generic problem of non-adiabatic errors in adiabatic evolution and state preparation, as well as general leakage errors due to spurious couplings to undesirable states. The method is based on the Magnus expansion: by correcting control pulses, we modify the Magnus expansion of an initially-given, imperfect unitary in such a way that the desired evolution is obtained. Applications to adiabatic quantum state transfer, superconducting qubits and generalized Landau-Zener problems are discussed.

Optimal control for perfect state transfer in linear quantum memory

A quantum memory is a system that enables transfer, storage, and retrieval of optical quantum states by ON/OFF switching of the control signal in each stage of the memory. In particular, it is known that, for perfect transfer of a single-photon state, appropriate shaping of the input pulse is required. However, in general, such a desirable pulse shape has a complicated form, which would be hard to generate in practice. In this paper, for a wide class of linear quantum memory systems, we develop a method that reduces the complexity of the input pulse shape of a single photon while maintaining the perfect state transfer. The key idea is twofold; (i) the control signal is allowed to vary continuously in time to introduce an additional degree of freedom, and then (ii) an optimal control problem is formulated to design a simple-formed input pulse and the corresponding control signal. Numerical simulations are conducted for Λ-type atomic media and networked atomic ensembles, to show the effectiveness of the proposed method.