Preparation Of Entanglement Research Articles

Efficient source-independent quantum conference key agreement

Quantum conference key agreement (QCKA) enables the unconditional secure distribution of conference keys among multiple participants. Due to challenges in high-fidelity preparation and long-distance distribution of multi-photon entanglement, entanglement-based QCKA is facing severe limitations in both key rate and scalability. Here, we propose a source-independent QCKA scheme utilizing the post-matching method, feasible within the entangled photon pair distribution network. We introduce an equivalent distributing virtual multi-photon entanglement protocol for providing unconditional security proof even in the case of coherent attacks. For the symmetry star network, compared with the previous n-photon entanglement protocol, the conference key rate is improved from O(η n ) to O(η2), where η is the transmittance from the entanglement source to one participant. Simulation results show that the performance of our protocol has multiple orders of magnitude advantages in the intercity distance. We anticipate that our approach will demonstrate its potential in the implementation of quantum networks.

Quantum Circuit-Based Proxy Blind Signatures: A Novel Approach and Experimental Evaluation on the IBM Quantum Cloud Platform

Abstract This paper presents a novel approach to proxy blind signatures in the realm of quantum circuits, aiming to enhance security while safeguarding sensitive information. The main objective of this research is to introduce a Quantum Proxy Blind Signature (QPBS) protocol that utilizes quantum logical gates and quantum measurement techniques. The QPBS protocol is constructed by initial phase, proximal blinding message phase, remote authorization and signature phase, remote validation and de-blinding phase. This innovative design ensures a secure mechanism for signing documents without revealing the content to the proxy signer, providing practical security authentication in a quantum environment under the assumption that the CNOT gates are securely implemented. Unlike existing approaches, our proposed QPBS protocol eliminates the need for quantum entanglement preparation, thus simplifying the implementation process. To assess the effectiveness and robustness of the QPBS protocol, we conduct comprehensive simulation studies in both ideal and noisy quantum environments on the IBM quantum cloud platform. The results demonstrate the superior performance of the QPBS algorithm, highlighting its resilience against repudiation and forgeability, key security concerns in the realm of proxy blind signatures. Furthermore, we have established authentic security thresholds (82.102%) in the presence of real noise, thereby emphasizing the practicality of our proposed solution.

Fast quantum state transfer and entanglement preparation in strongly coupled bosonic systems

Abstract Continuous U(1) gauge symmetry, which guarantees the conservation of total excitations in linear bosonic systems, will be broken when it comes to the strong-coupling regime where the rotation wave approximation (RWA) fails. Here we develop analytic solutions for multi-mode bosonic systems with XX-type couplings beyond RWA, and propose a novel scheme to implement high-fidelity quantum state transfer (QST) and entanglement preparation (EP) with high speed. The scheme can be realized with designated coupling strength and pulse duration with which the excitation number keeps unchanged regardless of the breakdown of the global U(1) symmetry. In QST tasks, we consider several typical quantum states and demonstrate that this method is robust against thermal noise and imperfections of experimental sequence. In EP tasks, the scheme is successfully implemented for the preparation of Bell states and W-type states, within a shortest preparation time.

Error-insensitive preparation of entangled states between a Josephson qubit and microwave photons via invariant-based shortcuts

Optimal preparation of quantum entanglement is of significance to information processing and state engineering. In this paper, an efficient scheme is proposed to implement error-insensitive generation of entangled states between a Josephson qubit and microwave photons by the technique of invariant-based shortcuts to adiabaticity. A superconducting qubit is dispersively coupled to a quantized cavity field of one-dimensional transmission line resonator. Within a considered subspace spanned by three composite states, we deal with an effective interaction of the composite system with two classical drivings. A maximally entangled qubit-photon state can be deterministically induced using a splitting-like quantum state transfer. To nullify the deviation errors of Rabi coupling and frequency detuning, we optimize the driving parameters and then make the entanglement creation insusceptible to these control imperfections. Thanks to the mitigation of deviation effects, robustness against the residual noisy environment could be obtained numerically. The proposed strategy could provide a promising avenue towards fast and robust information processing with superconducting circuit quantum electrodynamics.

Distant entanglement generation and controllable information transfer via magnon–waveguide systems

The generation of entanglement and information distribution among macroscopic systems which are spatially separated are of paramount importance in the realm of quantum networks and quantum communication. In this paper, we propose a scheme that enables the preparation of long-distance entanglement between two magnons and controllable information transfer from a giant atom to either magnon, where the two magnons can be positioned symmetrically or asymmetrically in relation to a giant atom, and all of the magnons and the atom are coupled to a microwave cavity-array waveguide. By considering significant frequency detuning, we can virtually excite photons and establish an indirect interaction between the giant atom and the two magnons. Through the modulation of atom–waveguide coupling rates, we can not only evenly transfer atomic excitation to both magnons, thereby generating maximally entangled states, but also selectively transmit the atomic state to a single magnon. It is our hope that our proposed scheme will prove valuable in the field of quantum communications.

Towards entanglement distillation between atomic ensembles using high-fidelity spin operations

Entanglement distillation is an essential ingredient for long-distance quantum communication. However, owing to their demanding requirements, integrating such entanglement distillation processing in scalable quantum devices remains an outstanding challenge. Here we propose the implementation of the filtering protocol in atomic ensembles, which are promising candidates for building quantum repeater nodes, and analyze the boost entanglement distribution rate considering different scenarios. Moreover, we demonstrate the key step of this approach with a proof-of-principle experiment in a rare-earth-ion-doped crystal (143Nd3+:Y2SiO5). Leveraging its multi-level structure and long-lived coherence, spin manipulations are implemented with an average fidelity exceeding 97.2%, leading to the preparation of entanglement between the electron and nuclear spins with a concurrence of 0.75 with a sample temperature of 100 mK. The versatility, robustness, and potential scalability of our proposal contribute to the construction of quantum repeaters and quantum networks based on atomic ensembles.

Robust and fast excitation fluctuations transfer between two membranes in an optomechanical system

The quantum state control or entanglement preparation for macroscopic matter is an attractive research. Optomechanical system provides an ideal platform to observe the quantum behaviors of macroscopic matter. In this paper, we present a scheme to implement the average excitation fluctuations transfer between two membranes in an optomechanical system via shortcut to adiabatic passage which is based on transitionless quantum driving. In order to quickly attain the transfer, we choose a suitable evolution path and optimize the experimental parameters. Numerical simulation demonstrates that the proposed scheme is robust against membrane damping and cavity decay. Furthermore, this idea can be used to generate entanglement of two membrane modes in a short time. Finally, we also discuss the experimental implementation of this scheme. This work may provide a new method for generating the macroscopic superposition state in the optomechanical system.

A perspective on quantum entanglement in optomechanical systems

Quantum entanglement in optomechanical systems plays an important role in the progress of quantum science and technology, such as the exploration of fundamental physics and quantum information processing. Although the physical law of quantum mechanics does not specifically limit the size of objects that carry the entangled states, the experimental preparation and detection of quantum entanglement in the macro world still face great challenges. Fortunately, with the experimental advances in recent years, several pioneering works have demonstrated non-local correlation and entanglement among mechanical oscillators or between oscillators and electromagnetic fields. In this perspective, we summarize the theoretical and experimental progress related to the macro entanglement states in optomechanical systems and outlook its future direction and potential applications.

Image preparations of multi-mode quantum image representation and their application on quantum image reproduction

Efficient and general quantum image representation and preparation are the precondition of quantum image processing. The multi-mode quantum image representation is compatible with many important color modes. Studying image preparation and image processing will help to further improve the universality of quantum image on different application fields. In this paper, we improve the multi-mode quantum image representation to reduce the difficulty of entanglement preparation. We give a detailed image preparation process and algorithm based on this proved representation. Then, to reduce the number of Not-gates in preparation circuits, the optimal preparation is proposed. Furthermore, we give the reproduction circuit based on these preparations. The preparation and reproduction experiments are performed on the IBM Quantum lab platform. The circuits and the Bell-state statistic histograms of the measurement collapse are given. The results show that the preparations and reproduction are correct and efficient.

Polychromatic Kerr nonlinearity within electromagnetically induced transparency window

We study the nonlinear effect in a three-level atomic system in Λ configuration. As two or more fields are confined within the common electromagnetically induced transparency (EIT) window, they directly disturb EIT dark state at the same time, which leads to the self- and cross-Kerr nonlinear interactions. Our scheme is different from the existed schemes based on three-level or multilevel systems only existing single type of nonlinear interactions. In the common EIT windows, the self- and cross-Kerr nonlinearities are established with suppressed linear absorption and our scheme can be generalized polychromatic Kerr nonlinearity. Because the atoms are almost trapped in the ground states and the atom population becomes unchanged, the scheme is robust to the atomic spontaneous emission. Our scheme is a promising avenue for preparation of squeezing and entanglement.

Robust and Fast Excitation Fluctuations Transfer between Two Membranes in an Optomechanical System

The quantum state control or entanglement preparation for macroscopic matter is an attractive research. Optomechanical system provides an ideal platform to observe the quantum behaviors of macroscopic matter. In this paper, we present a scheme to implement the average excitation fluctuations transfer between two membranes in an optomechanical system via shortcut to adiabatic passage which is based on transitionless quantum driving. In order to quickly attain the transfer, we choose a suitable evolution path and optimize the experimental parameters. Numerical simulation demonstrates that the proposed scheme is robust against membrane damping and cavity decay. Furthermore, this idea can be used to generate entanglement of two membrane modes in a short time. Finally, we also discuss the experimental implementation of this scheme. This work may provide a new method for generating the macroscopic superposition state in the optomechanicalsystem.

Heralded preparation of polarization entanglement via quantum scissors

Quantum entanglement is at the heart of quantum information sciences and quantum technologies. In the optical domain, the most common type of quantum entanglement is polarization entanglement, which is usually created in a postselection manner involving destructive photon detection and thus hindering further applications which require readily available entanglement resources. In this work, we propose a scheme to prepare multipartite entangled states of polarized photons in a heralded manner, i.e., without postselection. We exploit the quantum scissors technique to truncate a given continuous-variable entanglement into the target entangled states which are of hybrid discrete-continuous or solely discrete types. We consider two implementations of the quantum scissors: one modified from the original quantum scissors [Pegg et al., Phys. Rev. Lett. 81, 1604 (1998)] using single photons and linear optics and the other designed here using a type-II two-mode squeezer. We clarify the pros and cons of these two implementations as well as discussing practical aspects of the entanglement preparation. Our work illustrates an interface between various types of optical entanglement and the proposed quantum scissors techniques could serve as alternative methods for heralded generation of polarization entanglement.

Entanglement preparation and nonreciprocal excitation evolution in giant atoms by controllable dissipation and coupling

We investigate the dynamics of giant atom(s) in a waveguide QED scenario, where the atom couples to the coupled resonator waveguide via two sites. For a single giant atom setup, we find that the atomic dissipation rate can be adjusted by tuning its size. For the two giant atoms system, the waveguide will induce the controllable individual and collective dissipation as well as effective inter-atom coupling. As a result, we can theoretically realize the robust entangled state preparation and non-reciprocal excitation evolution. We hope our study can be applied in quantum information processing based on photonic and acoustic waveguide setup.

Adiabatic preparation of maximum entanglement in hybrid quantum systems with the Z 2 symmetry

Adiabatic preparation of maximum entanglement in hybrid quantum systems with the <i>Z</i> ₂ symmetry

Quantum metrology via chaos in a driven Bose-Josephson system

Entanglement preparation and signal accumulation are essential for quantum parameter estimation, which pose significant challenges to both theories and experiments. Here, we propose how to utilize chaotic dynamics in a periodically driven Bose-Josephson system for achieving a high-precision measurement beyond the standard quantum limit (SQL). Starting from an initial non-entangled state, the chaotic dynamics generates quantum entanglement and simultaneously encodes the parameter to be estimated. By using suitable chaotic dynamics, the ultimate measurement precision of the estimated parameter can beat the SQL. The sub-SQL measurement precision scaling can also be obtained via specific observables, such as population measurements, which can be realized with state-of-art techniques. Our study not only provides new insights for understanding quantum chaos and quantum-classical correspondence, but also is of promising applications in entanglement-enhanced quantum metrology.

Preparation and verification of two-mode mechanical entanglement through pulsed optomechanical measurements

We propose a protocol how to generate and verify bipartite Gaussian entanglement between two mechanical modes coupled to a single optical cavity, by means of short optical pulses and measurement. Our protocol requires neither the resolved sideband regime, nor low thermal phonon occupancy, and allows the generation and verification of quantum entanglement in less than a mechanical period of motion. Entanglement is generated via effective two-mode mechanical squeezing through conditioning position measurements. We study the robustness of entanglement to experimental deviations in mechanical frequencies and optomechanical coupling rates.

Two-step feedback preparation of entanglement for qubit systems with time delay

Quantum entanglement plays a fundamental role in quantum computation and quantum communication. Feedback control has been widely used in stochastic quantum systems to generate given entangled states since it has good robustness, where the time required to compute filter states and conduct filter-based control usually cannot be ignored in many practical applications. This paper designed two control strategies based on the Lyapunov method to prepare a class of entangled states for qubit systems with a constant delay time. The first one is bang–bang-like control strategy, which has a simple form with switching between a constant value and zero, the stability of which is proved. Another control strategy is switching Lyapunov control, where a constant delay time is introduced in the filter-based feedback control law to compensate for the computation time. Numerical results on a two-qubit system illustrate the effectiveness of these two proposed control strategies.

Maximal steady-state entanglement and perfect thermal rectification in non-equilibrium interacting XXZ chains

We propose a scheme for dissipative preparation of maximal entanglement in a two-qubit Heisenberg XXZ model interacting asymmetrically with two independent boson thermal reservoirs with different temperature. One reservoir is common to both qubits, while the other is connected with just one qubit. We analytically and numerically investigate the steady-state entanglement of the qubits, based on the Markovian quantum master equation. We study the influence of the inherent asymmetry induced by the asymmetrically couplings of qubits to the reservoirs, on the steady-state entanglement of the qubits. While the temperature gradient of reservoirs generally deteriorate quantum correlations, we show that in the presence of the inherent asymmetry, the maximal entanglement can revive by increasing temperature gradient, at high base temperature of the reservoirs. We find that by turning on the asymmetry, perfect rectification can be achieved without introducing any additional asymmetry to the system. We also discover that the obtained perfect rectification is associated with maximizing of the steady-state entanglement.

Fast population transfer and entanglement preparation among four superconducting flux qubits

We propose a scheme whereby we optimized the driven pulses applied on qubits to realize fast and robust population of quantum state transfer and entanglement generation between four superconducting flux qubits based on adiabatic passage. The quantum state was transferred from one qubit to another directly with high fidelity through applying an inverted set of pulses. Moreover, the resident time of the quantum state populated on the qubits could be controlled by adjusting the time delay between the driven pulses during the transfer process. Analysis of the dynamics demonstrates that the scheme is insensitive to inhomogeneous qubit–resonator coupling, and even for large detuning regimes of the qubit–resonator interaction, high-fidelity quantum state transfer and entanglement generation can be obtained. Our results also show that the effect of decoherence due to resonator decay and qubit relaxation could be negligible with currently existing technology.

Robust entanglement preparation against noise by controlling spatial indistinguishability

Initialization of composite quantum systems into highly entangled states is usually a must to enable their use for quantum technologies. However, unavoidable noise in the preparation stage makes the system state mixed, hindering this goal. Here, we address this problem in the context of identical particle systems within the operational framework of spatially localized operations and classical communication (sLOCC). We define the entanglement of formation for an arbitrary state of two identical qubits. We then introduce an entropic measure of spatial indistinguishability as an information resource. Thanks to these tools we find that spatial indistinguishability, even partial, can be a property shielding nonlocal entanglement from preparation noise, independently of the exact shape of spatial wave functions. These results prove quantum indistinguishability is an inherent control for noise-free entanglement generation.