Quantum State Transfer Research Articles

High-fidelity bosonic quantum state transfer using imperfect transducers and interference

We consider imperfect two-mode bosonic quantum transducers that cannot completely transfer an initial source-system quantum state due to insufficient coupling strength or other Hamiltonian non-idealities. We show that such transducers can generically be made perfect by using interference and phase-sensitive amplification. Our approach is based on the realization that a particular kind of imperfect transducer (one which implements a swapped quantum non-demolition (QND) gate) can be made into a perfect one-way transducer using feed-forward and/or injected squeezing. We show that a generic imperfect transducer can be reduced to this case by repeating the imperfect transduction operation twice, interspersed with amplification. Crucially, our scheme only requires the ability to implement squeezing operations and/or homodyne measurement on one of the two modes involved. It is thus ideally suited to schemes where there is an asymmetry in the ability to control the two coupled systems (e.g., microwave-to-optics quantum state transfer). We also discuss a correction protocol that requires no injected squeezing and/or feed-forward operation.

Arbitrated quantum signature scheme with quantum walk-based teleportation

Quantum walks can be applied for some quantum information processing tasks such as quantum search, element distinctness, state transfer and teleportation. In this paper, we present an arbitrated quantum signature scheme with quantum walk-based teleportation. The teleportation is used for the transmission of message copy from the signer Alice to the verifier Bob. The necessary entangled states for teleportation do not need to be prepared in advance in the initial phase and can be produced naturally via quantum walk in the signature phase. Furthermore, to resist against Bob’s existential forgery for Alice’s signature under known message attack in the previous arbitrated quantum signature proposals, we employ a random number and a public board in the verification phase. Security analyses show the suggested scheme is with impossibility of disavowal of Alice and Bob, impossibility of forgery of anyone. Discussions indicate that the scheme may not prevent the disavowal of Alice and we advance the potential improvements on it. Note that the proposed arbitrated quantum signature scheme may be feasible because quantum walks prove to be implemented in different physical systems and experiments.

Directional quantum state transfer in a dissipative Rydberg-atom-cavity system

Quantum state transfer is a basic task for quantum information processing, which can be easily executed using the coherent dynamics for a closed system instead of the dissipative dynamics for an open system. Here we propose a dissipation-assisted scheme to directionally transfer an arbitrary quantum state from the sender $A$ to the receiver $B$ by virtue of the Rydberg antiblockade mechanism, the laser-induced Raman transition, and the photon loss of an optical cavity. The prominent advantage of the current proposal is that it does not require accurate control over the relevant parameters of the system, as the target state is the steady state of the whole process. The effect of atomic spontaneous emission for the excited states is dramatically restricted by the adiabatic elimination, and a high population of the transferred state around $99%$ is achievable with the current experimental technology.

Swapping intraphoton entanglement to interphoton entanglement using linear optical devices

We propose a curious protocol for swapping the intra-photon entanglement between path and polarization degrees of freedom of a single photon to inter-photon entanglement between two spatially separated photons which have never interacted. This is accomplished by using an experimental setup consisting of three suitable Mach-Zehnder interferometers along with number of beam splitters, polarization rotators and detectors. Using the same setup, we have also demonstrated an interesting quantum state transfer protocol, symmetric between Alice and Bob. Importantly, the Bell-basis discrimination is not required in both the swapping and state transfer protocols. Our proposal can be implemented using linear optical devices.

Shuttling a single charge across a one-dimensional array of silicon quantum dots

Significant advances have been made towards fault-tolerant operation of silicon spin qubits, with single qubit fidelities exceeding 99.9%, several demonstrations of two-qubit gates based on exchange coupling, and the achievement of coherent single spin-photon coupling. Coupling arbitrary pairs of spatially separated qubits in a quantum register poses a significant challenge as most qubit systems are constrained to two dimensions with nearest neighbor connectivity. For spins in silicon, new methods for quantum state transfer should be developed to achieve connectivity beyond nearest-neighbor exchange. Here we demonstrate shuttling of a single electron across a linear array of nine series-coupled silicon quantum dots in ~50 ns via a series of pairwise interdot charge transfers. By constructing more complex pulse sequences we perform parallel shuttling of two and three electrons at a time through the array. These experiments demonstrate a scalable approach to physically transporting single electrons across large silicon quantum dot arrays.

Subradiant Bell States in Distant Atomic Arrays.

We study collective "free-space" radiation properties of two distant single-layer arrays of quantum emitters as two-level atoms. We show that this system can support a long-lived Bell superposition state of atomic excitations exhibiting strong subradiance, which corresponds to a nonlocal excitation of the two arrays. We describe the preparation of these states and their application in quantum information as a resource of nonlocal entanglement, including deterministic quantum state transfer with high fidelity between the arrays representing quantum memories. We discuss experimental realizations using cold atoms in optical trap arrays with subwavelength spacing, and analyze the role of imperfections.

Atomic quadrature squeezing and quantum state transfer in a hybrid atom–optomechanical cavity with two Duffing mechanical oscillators

In this paper, we investigate theoretically the quantum state transfer in a laser driven hybrid optomechanical cavity with two Duffing-like anharmonic movable end mirrors containing an ensemble of identical two-level trapped atoms. The quantum state transfer from the Bogoliubov modes of the two anharmonic oscillators to the atomic mode results in the atomic quadrature squeezing beyond the standard quantum limit of 3 dB which can be controlled by both the optomechanical and atom-field coupling strengths. Interestingly, the generated atomic squeezing can be made robust against the noise sources by means of the Duffing anharmonicity. Moreover, the results reveal that the presence of the Duffing anharmonicity provides the possibility of transferring strongly squeezed states between the two mechanical oscillators in a short operating time and with a high fidelity.

Fast and robust quantum control for multimode interactions using shortcuts to adiabaticity.

Adiabatic quantum control is a very important approach for quantum physics and quantum information processing (QIP). It holds the advantage with robustness to experimental imperfections but accumulates more decoherence due to the long evolution time. Here, we propose a universal protocol for fast and robust quantum control in multimode interactions of a quantum system by using shortcuts to adiabaticity. The results show this protocol can speed up the evolution of a multimode quantum system effectively, and it can also keep the robustness very good while adiabatic quantum control processes cannot. We apply this protocol for the quantum state transfer in QIP in the photon-phonon interactions in an optomechanical system, showing a perfect result. These good features make this protocol have the capability of improving effectively the feasibility of the practical applications of multimode interactions in QIP in experiment.

Fast Hybrid Quantum State Transfer and Entanglement Generation via No Transition Passage

AbstractQuantum information processing requires information or entanglement that can be transferred or distributed from one location to another with high fidelity. Here, a scheme for faithful quantum state transfer and entanglement generation based on the hybrid opto‐electro‐mechanical (OEM) systems in a fast and deterministic way is proposed. By applying invariant‐based inverse engineering to the interaction Hamiltonian, the couplings in the OEM system can be controlled by asynchronized driving fields, which is convenient to be realized in practice. Taking the systematic decoherence into consideration, the numerical simulation shows that the scheme can be implemented with less time and high fidelity. Therefore, the scheme provides a promising way for robust on‐chip converting of low‐frequency electrical signal into much higher‐frequency optical signal, and thus enabling large‐scale quantum information networks to grow in size and complexity.

Landau–Zener Topological Quantum State Transfer

AbstractFast and robust quantum state transfer (QST) is a major requirement in quantum control and in scalable quantum information processing. Topological protection has emerged as a promising route for the realization of QST robust against sizable imperfections in the network. Here, a scheme is presented for robust QST of topologically protected edge states in a dimeric Su–Schrieffer–Heeger spin chain assisted by Landau–Zener tunneling. As compared to topological QST protocols based on Rabi flopping proposed in recent works, the method is more advantageous in terms of robustness against both diagonal and off‐diagonal disorder in the chain, without a substantial increase of the interaction time.

Pretty good state transfer on 1-sum of star graphs

AbstractLetAbe the adjacency matrix of a graphGand supposeU(t) = exp(itA). We say that we have perfect state transfer inGfrom the vertexuto the vertexvat timetif there is a scalarγof unit modulus such thatU(t)eu=γ ev. It is known that perfect state transfer is rare. So C.Godsil gave a relaxation of this definition: we say that we have pretty good state transfer fromutovif there exists a complex numberγof unit modulus and, for each positive realϵthere is a timetsuch that ‖U(t)eu–γ ev‖ <ϵ. In this paper, the quantum state transfer on 1-sum of star graphsFk,lis explored. We show that there is no perfect state transfer onFk,l, but there is pretty good state transfer onFk,lif and only ifk=l.

Coherent microwave-to-optical conversion by three-wave mixing in a room temperature atomic system.

We experimentally observe coherent generation of a near-infrared optical field through a three-wave mixing phenomenon in an atomic energy level scheme of Rb85 atoms. This nonlinear generation process in a centro-symmetric thermally broadened atomic system is made possible through a novel interaction between induced electric and magnetic dipoles. The two-photon and three-photon coherence present in our scheme eliminates excited state decoherence. Thus, our scheme represents a minimal optical decoherence scheme which could be used to transfer quantum states between microwave-to-optical frequency regimes with near-unit fidelity.

Low temperature dynamics of netral atoms for quantum logic

We study from the point of view of quantum logic the properties of the collective oscillations of two Rydberg atoms in two harmonic traps. The difference in the frequency of two normal modes of motion expands with the difference in the mass of the two atoms. The probability of excitation of the motional quanta due to the strong dipole-dipole interaction can be made to be sufficiently small. Based on the normal modes of motion we present a scheme for quantum state transfer which is useful for quantum information process and for precision spectroscopy of atoms that lack suitable transitions for efficient laser cooling, internal state preparation, and detection.

Interference of the signal from a local dynamical process with the quantum state propagation in spin chains

The effect of a local instantaneous quantum dynamical process (QDP), either unitary or non-unitary, on the quantum state transfer through a unitary Hamiltonian evolution is investigated for both integrable and non-integrable dynamics. There are interference effects of the quantum state propagation and the QDP signal propagation. The state transfer fidelity is small for further sites, from the site where the information is coded, indicating a finite speed for the propagation of the quantum correlation. There is a small change in the state transfer fidelity for the case of the non-unitary QDP intervening in the the background of unitary dynamics. In the case of the unitary QDP, the change is more pronounced, with a substantial increase in the fidelity for appropriate sites and times. For the non-integrable case, namely a kicked Harper model, the state transfer fidelity is quite large for further sites for short times, indicating that a finite speed for the propagation of the quantum correlation cannot be defined.

Pretty good quantum state transfer in asymmetric graphs via potential

We construct infinite families of graphs in which pretty good state transfer can be induced by adding a potential to the nodes of the graph (i.e. adding a number to a diagonal entry of the adjacency matrix). Indeed, we show that given any graph with a pair of cospectral nodes, a simple modification of the graph, along with a suitable potential, yields pretty good state transfer between the nodes. This generalizes previous work, concerning graphs with an involution, to asymmetric graphs.

Optomechanical state transfer between two distant membranes in the presence of non-Markovian environments**Project supported by the National Natural Science Foundation of China (Grant Nos. 11704205, 11704026, 21773131, and 11574167), China Postdoctoral Science Foundation (Grant No. 2018M632437), the Natural Science Foundation of Ningbo City (Grant No. 2018A610199), and K C Wong Magna Fund in Ningbo University, China.

The quantum state transfer between two membranes in coupled cavities is studied when the system is surrounded by non-Markovian environments. An analytical approach for describing non-Markovian memory effects that impact on the state transfer between distant membranes is presented. We show that quantum state transfer can be implemented with high efficiency by utilizing the experimental spectral density, and the performance of state transfer in non-Markovian environments is much better than that in Markovian environments, especially when the tunneling strength between the two cavities is not very large.

Scaling Phononic Quantum Networks of Solid-State Spins with Closed Mechanical Subsystems

Phononic quantum networks feature distinct advantages over photonic networks for on-chip quantum communications, providing a promising platform for developing quantum computers with robust solid-state spin qubits. Large mechanical networks including one-dimensional chains of trapped ions, however, have inherent and well-known scaling problems. In addition, chiral phononic processes, which are necessary for conventional phononic quantum networks, are difficult to implement in a solid-state system. To overcome these seemingly unsolvable obstacles, we have developed a new network architecture that breaks a large mechanical network into small and closed mechanical subsystems. This architecture is implemented in a diamond phononic nanostructure featuring alternating phononic crystal waveguides with specially-designed bandgaps. The implementation also includes nanomechanical resonators coupled to color centers through phonon-assisted transitions as well as quantum state transfer protocols that can be robust against the thermal environment.

Pretty good state transfer via adaptive quantum error correction

We examine the role of quantum error correction (QEC) in achieving pretty good quantum state transfer over a class of $1$-d spin Hamiltonians. Recasting the problem of state transfer as one of information transmission over an underlying quantum channel, we identify an adaptive QEC protocol that achieves pretty good state transfer. Using an adaptive recovery and approximate QEC code, we obtain explicit analytical and numerical results for the fidelity of transfer over ideal and disordered $1$-d Heisenberg chains. In the case of a disordered chain, we study the distribution of the transition amplitude, which in turn quantifies the stochastic noise in the underlying quantum channel. Our analysis helps us to suitably modify the QEC protocol so as to ensure pretty good state transfer for small disorder strengths and indicates a threshold beyond which QEC does not help in improving the fidelity of state transfer.

Perfect Quantum State Transfer in a Superconducting Qubit Chain with Parametrically Tunable Couplings

Faithfully transferring the quantum state is essential for quantum information processing. Here we demonstrate a fast (in 84 ns) and high-fidelity (99.2%) transfer of arbitrary quantum states in a chain of four superconducting qubits with nearest-neighbor coupling. This transfer relies on full control of the effective couplings between neighboring qubits, which is realized only by our parametrically modulating the qubits without increasing circuit complexity. Once the couplings between qubits fulfill a specific ratio, perfect quantum state transfer can be achieved in a single step, and is therefore robust to noise and accumulation of experimental errors. This quantum state transfer can be extended to a larger qubit chain and thus adds a desirable tool for future quantum information processing. The demonstrated flexibility of the coupling tunability is suitable for quantum simulation of many-body physics, which requires different configurations of qubit couplings.

Deterministic quantum state transfer between remote atoms with photon-number superposition states

We propose a protocol for quantum networking based on deterministic quantum state transfer between distant memory nodes using photon-number superposition states (PNSS). In the suggested scheme, the quantum nodes are single atoms confined in high-finesse optical cavities linked by photonic channels. The quantum information written in a superposition of atomic Zeeman states of sending system is faithfully mapped through cavity-assisted Raman scattering onto PNSS of linearly polarized cavity photons. The photons travel to the receiving cavity, where they are coherently absorbed with unit probability creating the same superposition state of the second atom, thus ensuring high-fidelity transfer between distant nodes. We develop this approach at first for photonic qubit and show that this superposition state is no less reliably protected against the propagation losses compared to the single-photon polarization states, whereas the limitation associated with the delivery of more than one photon does not affect the process fidelity. Then, by preserving the advantages of qubits, we extend the developed technique to the case of state transfer by photonic qutrit, which evidently possesses more information capacity. This reliable and efficient scheme promises also a successful distribution of entanglement over long distances in quantum networks.