Pair Coherent States Research Articles

Improved experimental scheme for the generation of pair coherent state in traveling-wave optical fields

Abstract Pair coherent state (PCS) is a two-mode non-Gaussian state recently generated within spatially confined superconducting cavities. Under typical conditions, it is unsuitable for performing global quantum missions in open space. Several methods have been proposed to generate this state with the capability to propagate unrestrictedly. However, these methods employed an excessive amount of unnecessary physical resources or relied on coherent displacement within the low regime. This paper presents a novel experimental approach to generate this state, specifically designed for facilitating long-distance quantum information processing and communication tasks. The method involves the utilization of two weak cross-Kerr nonlinear media, two balanced beam splitters, and an on/off photodetector. Furthermore, the input comprises three CSs with high amplitudes. These physical resources are potentially accessible within existing technology. The analysis of success probability and fidelity demonstrates that the PCS can be successfully generated with a high coherent parameter amplitude, even in scenarios where the photodetector efficiency is low, provided that the coherent amplitudes are sufficiently high.

Application of generalized photon-added pair coherent state to quantum teleportation via atom-field entangled channel

Application of generalized photon-added pair coherent state to quantum teleportation via atom-field entangled channel

The Physical Transient Spectrum and Squeezing of a Three-Level Atom Interacting with Two-Mode Field in Finite Pair Coherent State in the Presence of a Classical External Field

The Physical Transient Spectrum and Squeezing of a Three-Level Atom Interacting with Two-Mode Field in Finite Pair Coherent State in the Presence of a Classical External Field

Enhancing quantum features and teleportation fidelity of two-mode non-Gaussian states using conditional measurements

The family of two-mode non-Gaussian entangled states, including the pair coherent states (PCSs) and their genealogies, has been extensively investigated regarding their quantum properties and their practical applications in quantum information. Specifically, certain states, such as the multiphoton catalytic pair coherent states (MCPCSs), have been newly introduced under specific experimental conditions. For a more feasible approach, in this paper, we introduce novel nonclassical states obtained by subtracting photons through conditional measurements using beam splitters applied to the two modes of the PCSs. These states are called pair coherent states with conditional measurements (PCSCMs). Our purpose is to demonstrate that the quantum features, such as entanglement, Einstein–Podolsky–Rosen (EPR) correlation, EPR steering, and the average fidelity in teleportation can be enhanced in comparison with both the original PCSs and the MCPCSs. In specific cases, several characteristics are observed in PCSCMs but not inspected in both PCSs and MCPCSs. In our findings, we prove that the quantum characteristics within the PCSCMs are influenced not just by the number of detected photons, denoted by variables k and l, but also by the discrepancy in photon numbers, especially by the difference of k − l.

Enhancement of non-Gaussianity and nonclassicality of pair coherent states by superposition of photon addition and subtraction

Pair coherent states (PCSs) as a kind of two-mode non-Gaussian and nonclassical states were introduced and studied. Some nonclassical characteristics of them such as two-mode sum-squeezing, two-mode antibunching, and entanglement have been well investigated. In this paper, we focus on studying the superposition of photon addition and subtraction to the PCSs called superposition of photon-added and photon-subtracted pair coherent states (SPAPSPCSs). Our main purpose is to show that the non-Gaussian feature and all the above-mentioned nonclassical properties of the SPAPSPCSs can be enhanced compared with the photon-added-and-subtracted two modes pair coherent states (PAASTMPCSs) and the original PCSs. In general, we demonstrate that the SPAPSPCSs have more enhanced non-Gaussian character and nonclassical properties than the PCSs and the PAASTMPCSs by examining the negativity of the Wigner function. Specifically, we indicate that both the SPAPSPCSs and the PAASTMPCSs can exist in two-mode sum-squeezing while the original PCSs (without photon-addition and photon-subtraction) cannot, and the degree of squeezing is stronger in the SPAPSPCSs than in the PAASTMPCSs. The obtained results also indicate that the superposition of photon addition and subtraction of the SPAPSPCSs plays a vital role in enhancing the two-mode antibunching property and the entanglement degree compared with the PCSs and the PAASTMPCSs.

Enhancement of dynamical entanglement in a dispersive two-mode Jaynes–Cummings model via superposition of photon-added pair coherent state

In this paper, we introduce a new non-Gaussian state called superposition of photon-added pair coherent state (SPAPCS) by superposition addition of photons to two modes of a pair coherent state (PCS). It is demonstrated that the SPAPCS has an enhanced non-Gaussian property by testing its Wigner function when increasing the number of photons added to two modes of the PCS. We use the field as a SPAPCS to study a dynamical entanglement in a dispersive two-mode Jaynes–Cummings model in dissipation atom-field interaction. We detect the dynamical entanglement degrees of the global system and subsystems by using the linear entropy criteria. The obtained results show the dynamical entanglement degrees can be enhanced by the phase damping effect as well as the superposition adding photons to two modes of the field in SPAPCS.

Experimental Realization and Characterization of Stabilized Pair-Coherent States

Experimental Realization and Characterization of Stabilized Pair-Coherent States

QUANTUM TELEPORTATION OF ENTANGLED STATES VIA GENERALIZED PHOTON-ADDED PAIR COHERENT STATE

In this paper, we study the quantum teleportation of an unknown atomic state based on the two-photon Jaynes-Cummings model, consisting of an effective two-level atom with a two-mode field in the generalized photon-added pair coherent state (GPAPCS). By applying the detecting method, we use a scheme that includes two two-level atoms and a cavity field to teleport the unknown atomic state from a sender to a receiver. The results show that the number of photons added to the field and the intensity of the initial field influence the average fidelity and success probability of the teleportation process. The time-evolution dependence of the average fidelity is also considered and compared for the field in the pair coherent state and in the GPAPCS.

Competition between Two-Photon Driving, Dissipation, and Interactions in Bosonic Lattice Models: An Exact Solution.

We present an exact solution in arbitrary dimensions for the steady states of a class of quantum driven-dissipative bosonic models, where a set of modes is subject to arbitrary two-photon driving, single-photon loss, and a global Hubbard (or Kerr)-like interaction. Our solutions reveal a wealth of striking phenomena, including the emergence of dissipative phase transitions, nontrivial mode competition physics and symmetry breaking, and the stabilization of many-body SU(1,1) pair-coherent states. Our exact solutions enable the description of spatial correlations, and are fully valid in regimes where traditional mean-field and semiclassical approaches break down.

Nonclassical properties of a non-degenerate parametric amplifier

Nonclassical properties of electromagnetic radiation propagating through a non-degenerate parametric amplifier (NDPA) are investigated. A complete quantum mechanical description is being used to describe the system. Under rotating wave approximation, the exact analytical solutions of the Heisenberg’s equations of motion for signal and idler modes are used to investigate the existence of various nonclassical properties of the radiation fields. These nonclassical properties include squeezing, intermodal entanglement and antibunching. The analytical results confirm the presence of these nonclassical properties for both the input composite number and coherent states. In addition, mixed mode squeezing is observed for input pair coherent states in both the quadratures. The analytical results are compared with their numerical counterpart obtained by QuTiP. The perfect matching of these results justifies the correctness of the analytical results.

Atomic Marginal Distribution and Squeezing Phenomena of Correlated Two Modes Interacting with a Three-Level Atom in the Presence of an External Classical Field

The influence of the external classical field on a correlated two-mode of the electromagnetic field interacting with a three-level atom in the Λ structure is studied. A rotation of the atomic basis is used to remove the classical field terms. The time-dependent wave function is obtained by solving the Schrödinger equation. The influence of the classical field on the phenomenon of revival, collapse, squeezing, and marginal atomic distribution are discussed. In our analysis, the cavity field is prepared in the entangled pair coherent states and the atomic system in the upper state. The results showed that the occupation of the atomic level is significantly affected by the addition of the classical field. The presence of the classical field reduces the squeezing intervals and the extreme values of the atomic marginal distribution.

Generalized entanglement measure for continuous-variable systems

Concurrence, introduced by Hill and Wootters [Hill and Wootters, Phys. Rev. Lett. 78, 5022 (1997)], provides an important measure of entanglement for a general pair of qubits that is strictly positive for entangled states and vanishes for all separable states. We present an extension of the entanglement measure to general pure continuous variable states of multiple degrees of freedom by generalizing the Lagrange's identity and wedge product framework proposed by Bhaskara and Panigrahi [Bhaskara and Panigrahi, Quantum Inf. Process. 16, 118 (2017)] for pure discrete-variable systems in arbitrary dimensions and extending the concept to mixed continuous-variable states. A family of faithful entanglement measures is constructed that admits necessary and sufficient conditions for separability across arbitrary bipartitions presented by Vedral et al. [Vedral, Plenio, Rippin, and Knight, Phys. Rev. Lett. 78, 2275 (1997)]. The computed entanglement measure in the present approach for general Gaussian states, pair-coherent states, and non-Gaussian continuous-variable Bell states matches with known results. We also quantify entanglement of phase-randomized squeezed states and superposition of squeezed states. Our results also simplify several results in quantum entanglement theory.

Sum squeezing, entanglement and quantum teleportation of the superposition of photon-added pair coherent state

In this paper, we study some non-classical properties of the superposition of photon-added pair coherent state (SPAPCS) such as two-mode sum squeezing and entanglement. The obtained results show that this state has two-mode sum squeezing behavior but the pair coherent state does not. The degree of squeezing of the SPAPCS is enhanced as more and more photons are added to the two modes of the original pair coherent state. Besides, this state is an entangled state and the entanglement degree can be enhanced by adding photons to both modes of the state. When using the SPAPCS as an entangled resource for a coherent state quantum teleportation, it is shown that the quantum teleportation process is successful and the average fidelity of the process can be higher than that of the case where the original pair coherent state is used if the parameters are selected appropriately.

Dynamical Properties of the Field In Generalized Photon-Added Pair Coherent State in the Jaynes-Cummings Model

Dynamical Properties of the Field In Generalized Photon-Added Pair Coherent State in the Jaynes-Cummings Model

Passive decoy state phase matching quantum key distribution

In this paper, a passive decoy state phase matching quantum key distribution scheme is proposed based on the heralded pair coherent state light source to make the protocol more practical and safe. Without changing the intensity of the light source, we can derive four different data sets by dividing the raw key data into four groups according to the combined results of detectors in source end. The scheme can make use of the different data sets to estimate the parameters and extract the secret key. The key generation rate formula is derived after the parameter estimation. The performance of the proposed scheme is analyzed with and without taking statistical fluctuation into consideration. The simulation results show that compared with the existing active decoy-state method, the proposed passive method has slightly lower key rate when the transmission distance is short, and has obviously higher key rate when the transmission distance exceeds 406[Formula: see text]km. The maximum safety transmission distance of the proposed scheme is 452[Formula: see text]km which is relatively further. According to the influence of statistical fluctuation, the performance of the proposed scheme declines as the length of the data falls. Even though the data size is [Formula: see text], the max safety transmission distance is also more than 400[Formula: see text]km.

Detecting nonclassicality and non-Gaussianity by the Wigner function and quantum teleportation in photon-added-and-subtracted two modes pair coherent state

We introduce a new state called photon-added-and-subtracted two modes pair coherent state (PAASTMPCS) by simultaneously adding and subtracting photons to the different modes of a pair coherent state. Its nonclassical and non-Gaussian properties are strengthened by the negative values of its Wigner function as the numbers of photons added or substracted increases. Based on the linear entropy criterion, we indicate that the PAASTMPCS is an entangled state. When increasing the numbers of photons added or substracted to a pair coherent state, the degree of entanglement in the PAASTMPCS is enhanced compared with the original pair coherent state. By using a PAASTMPCS as a non-Gaussian entangled resource, the quantum teleportation process is studied in detail. The results show that the number sum and phase difference measurements protocol is more appropriate than the orthogonal quadrature components measurements protocol in the quantum teleportation process of a coherent state.

Continuous-variable Clauser-Horne Bell-type inequality: A tool to unearth the nonlocality of continuous-variable quantum-optical systems

We consider a multiphoton Bell-type inequality to study nonlocality in four-mode continuous variable systems, which goes beyond two-photon states and can be applied to mixed as well as states with fluctuating photon number. We apply the inequality to a wide variety of states such as pure and mixed Gaussian states (including squeezed thermal states) and non-Gaussian states. We consider beam splitters as a model for leakage and show that the inequality is able to detect nonclassicality of noisy Gaussian states as well. Finally, we investigate nonlocality in pair-coherent states and entangled coherent states, which are prominent examples of nonclassical, non-Gaussian states.

Effect of a deformed cavity on a time-dependent quantum system containing an entangled two modes.

In this manuscript, the phenomenon of time dependence is treated using the integral property of a model consisting of interaction of an atom with a cavity in which a bi-mode field of an amplifier type. The exact solution is obtained through the Schrodinger equation, followed by the wave function characteristic of the proposed system. The effect of both the deformed pair coherent states and the time dependence on some statistical quantities are studied. The phenomena of revival and collapse are studied by computing the atomic inversion. Moreover, the entanglement between the parts of the quantum system is studied, and the periods of squeezing are determined by entropy squeezing and variance squeezing. The results are also compared and statistical quantities linked together.

Dephasing Process of a Single Atom Interacting with a Two-Mode Field.

We consider the interaction of a qubit system with a two-mode field in the presence of multi-photon transition and phase damping effect. We use the master equation to obtain the density operator when the qubit is initially prepared in its excited state and the field is in a finite-dimensional pair coherent state. The properties of the considered system, such as the population inversion, amount of the mixedness, parameter estimation, and squeezing, are explored for one- and two-photon transitions. The effects of photon addition to the field and phase damping on the evaluation of these quantumness measures are also investigated.

Measurement-device-independent quantum key distribution protocols against collective noise

In order to eliminate the influence of the channel noise, two new measurement-device-independent quantum key distribution (MDI-QKD) protocols are proposed with logical quantum states. They can resist collective-dephasing noise and collective-rotation noise, respectively. This paper produces logical quantum states by adding the auxiliary light sources, the CNOT operations and the Hadamard transforms in the system model. The main light sources and auxiliary light sources are flexible and easily implemented, since they can be weak coherent state (WCS) sources, heralded single-photon sources (HSPSs) or heralded pair coherent state (HPCS) sources. To generate one key bit, the new MDI-QKD protocols only need one logical qubit with two particles so that they have high qubit efficiency. Moreover, the new protocols also use partial Bell-state measurement (BSM) which is very easily implemented with existing technologies.