Two-mode Squeezed Vacuum State Research Articles

Effect of noisy environment on secure quantum teleportation of unimodal Gaussian states

Quantum networks rely on quantum teleportation, a process where an unknown quantum state is transmitted between sender and receiver via entangled states and classical communication. In our study, we utilize a continuous variable two-mode squeezed vacuum state as the primary resource for quantum teleportation, shared by Alice and Bob, while exposed to a squeezed thermal environment. Secure quantum teleportation necessitates a teleportation fidelity exceeding 2/3 and the establishment of two-way steering of the resource state. We investigate the temporal evolution of steering and teleportation fidelity to determine critical parameter values for secure quantum teleportation of a coherent Gaussian state. Our findings reveal constraints imposed by temperature, dissipation rate, and squeezing parameters of the squeezed thermal reservoir on the duration of secure quantum teleportation. Intriguingly, we demonstrate that increasing the squeezing parameter of the initial state effectively extends the temporal window for a successful secure quantum teleportation.

Practical approach to extending baselines of telescopes using continuous-variable quantum information

Abstract Interferometric telescopes are instrumental for the imaging of distant astronomical bodies, but optical loss heavily restricts how far telescopes in an array can be placed from one another, leading to a bottleneck in the resolution that can be achieved. An entanglement-assisted approach to this problem has been proposed by (Gottesman et al 2011 Phys. Rev. Lett. 109 070503), as a possible solution to the issue of optical loss if the entangled state can be distributed across long distances by employing a quantum repeater network. In this paper, we propose an alternative entanglement-assisted scheme that interferes a two-mode squeezed vacuum state with the astronomical state and then measures the resulting state by means of homodyne detection. We use a continuous-variable approach and compute the Fisher information with respect to the mutual coherence of the astronomical source. We show that when the Fisher information is observed cumulatively at the rate at which successful measurements can be performed, our proposed scheme does not outperform the traditional direct detection approach or the entanglement-assisted approach of GJC12.

Mode-selective photon-added two-mode squeezed vacuum state and its entanglement properties

A class of non-Gaussian entangled states is introduced by applying the nonlocal single-photon addition to two-mode squeezed vacuum state and the properties of entanglement are numerically investigated according to linear entropy and Einstein–Podolsky–Rosen (EPR) steering. After the nonlocal single-photon addition operation, Wigner function of the generated state appears some negative region and loses its Gaussian property in phase space. In essence, non-Gaussian entangled states are generated after applying nonlocal single-photon addition. Additionally, by studying the linear entropy and EPR steering, we find that single-photon addition can enhance their entanglement degree and non-Gaussian steering can be witnessed in a large range of squeezing parameter for the second-order quadratures, which may provide a well application in the fields of quantum information processing.

Security enhancement of amplitude-shift keying-type asymmetric quantum communication systems

Recently, we proposed an amplitude-shift keying asymmetric quantum communication system and evaluated its reliability when using the quasi-Bell state and two-mode squeezed vacuum state (TSVS) as an entangled light source. In this paper, we evaluate the security of the system and find that either security or reliability can be enhanced depending on the entangled light sources. We also consider an approach to enhance the security of the system as well as its reliability by increasing the number of signal modes. Interestingly, we find that the quasi-Bell state always performs better than the TSVS under certain conditions.

Enhancement of teleportation average fidelity via photon addition operation

In this paper, using the linear entropy criterion to quantify the degree of entanglement, we demonstrate that the addition of photons can enhance the entanglement degree of the photon-added two-mode squeezed vacuum states (PATMSVSs). Besides, the entanglement degree can approach ideal in case of squeezing parameter or number of added photons is high. When using PATMSVSs as entanglement resources to teleport a coherent state via a canonical protocol, the results show that the average fidelity of the quantum teleportation process is enhanced by the photon addition operation. The average fidelity increases as the number of photons added to the two-mode increases. In addition, we show that an enhancement in average fidelity can also be achieved by increasing the squeezing parameter of the TMSVS.

Quantum illumination with noisy probes: Conditional advantages of non-Gaussianity

Entangled states, like the two-mode squeezed vacuum state, are known to give quantum advantage in the illumination protocol, a method to detect a weakly reflecting target submerged in a thermal background. We use non-Gaussian photon-added and -subtracted states, affected by local Gaussian noise on top of the omnipresent thermal noise, as probes in the illumination protocol. Based on the difference between the Chernoff bounds obtained with the coherent state and the non-Gaussian state having equal signal strengths, whose positive values denote quantum advantage in illumination, we highlight the hierarchy among non-Gaussian states, which is compatible with correlations per unit signal strength, although the Gaussian states offer the best performance. Interestingly, such hierarchy is different when comparisons are made using the Chernoff bounds. The entire analysis is performed in the presence of different imperfect apparatus like faulty twin-beam generator, imperfect photon addition (subtraction) as well as with noisy non-Gaussian probe states.

Detection scheme using a beam splitter and on-off detectors for non-Gaussian state-based quantum illumination with attenuation

Quantum illumination is an entanglement-based protocol for target detection. The use of a two-mode squeezed vacuum (TMSV) state as a type of Gaussian state has been widely discussed. In our previous study, we found that the quasi-Bell state, which is a non-Gaussian state, outperforms the TMSV state in the quantum illumination protocol with attenuation. In this paper, we construct a detection scheme using practical elements and demonstrate that it can outperform the TMSV state without using the photon-number resolution.

Photon subtraction with a Mach–Zehnder interferometer and its application to entanglement enhancement

Photon subtraction (PS) is an important operation for optic quantum information processing. Conventional PS is implemented using a single linear beam splitter (BS) and photon detector. However, in this study, we show that the PS effect can be enhanced using two beam splitters and an optional phase modulator. This can be considered PS with an extended version of the well-known Mach–Zehnder (MZ) interferometer. By tuning the transmittance of the two beam splitters and phase modulator, the probability of success can be considerably improved over that of the original PS scheme with a single BS and photon detector. Moreover, if applied to a single-photon input, our proposed scheme can even implement deterministic PS, which is almost impossible for the original scheme with a single BS and photon detector. Owing to the higher probability of success, applying the PSMZ method to the entanglement enhancement of a very weak two-mode squeezed vacuum state is straightforward. Our result is helpful for improving the yield of output entanglement.

Continuous Variable Quantum Teleportation in a Dissipative Environment: Comparison of Non‐Gaussian Operations Before and After Noisy Channel

AbstractThis article explores the relative advantages in continuous‐variable quantum teleportation when non‐Gaussian operations, namely, photon subtraction, addition, and catalysis, are performed before and after interaction with a noisy channel. The resource state for teleporting unknown coherent and squeezed vacuum states is generated using two distinct strategies: i) Implementation of non‐Gaussian operations on two mode squeezed vacuum (TMSV) state before interaction with a noisy channel, ii) Implementation of non‐Gaussian operations after interaction of TMSV state with a noisy channel. The results show that non‐Gaussian operations can enhance teleportation fidelity in a dissipative environment. However, the most advantageous non‐Gaussian operation and appropriate strategy depend on the state and channel parameters. The results suggest that employing such strategies can be advantageous in other non‐Gaussian continuous variable quantum information (QIP) processing tasks in a dissipative environment.

Reduction of g2(0) value in heralded spontaneous parametric down-conversion sources using photon number resolving detectors

Single Photon Sources (SPSs) play a pivotal role in fields such as quantum communication and quantum cryptography by generating information in a secure manner. However, realizing the ideal emission of single photons with high efficiency is still a theoretical model. This leads to the presence of multiphoton components in SPSs, which could potentially compromise security. This study focuses on enhancing the purity of a class of sources by characterizing their photon number distribution and mitigating the impact of the multiphoton components. We propose the use of Photon Number Resolving Detectors (PNRD) as a technique to exclude multiphoton contributions, particularly in sources like Spontaneous Parametric Down Conversion sources, where emitted photons can be represented as Two-Mode Squeezed Vacuum states. By analyzing the second-order cross-correlation function, g2(0), using either PNRD or Single Photon Detectors, we can quantify the reduction in multiphoton contributions.

Analysis of quantum properties of two-mode coupled Harmonic Oscillator based on the entangled state representation

The quantum oscillator model plays a significant role in quantum optics and quantum information and has been one of the hot research topics in related fields. Inspired by the single-mode linear harmonic oscillator and the two-mode entangled state representation, this paper constructs a two-mode coupled harmonic oscillator. Different from the quantum transformation method used in previous literature, this paper directly uses the entangled state representation to solve its energy eigenvalues ​​and eigenfunctions easily. Compared with the one-mode harmonic oscillator, the energy eigenvalues ​​and eigenfunctions of this two-mode coupled harmonic oscillator are continuous.<br>Using the matrix theory of quantum operators, we derive the transformation and inverse transformation of the time evolution operator corresponding to the two-mode coupled harmonic oscillator. In addition, using the entangled state representation, the specific form of the time evolution of the two-mode vacuum state under the action of the oscillator is obtained. Through the analysis of quantum fidelity, it is found that the fidelity of the output quantum state decreases with the increase of the oscillator frequency, and the fidelity eventually tends to zero with the increase of time.<br>When analyzing the orthogonal squeezing properties of the output quantum state, this type of two-mode oscillator does not have the orthogonal squeezing effect, but instead has a strong quantum dissipation effect. This conclusion is further verified by the quasi-probability distribution Q function of the quantum state phase space. Therefore, the two-mode coupled harmonic oscillator has a major reference value in quantum control such as quantum decoherence and quantum information transmission.<br>Like the two-mode squeezed vacuum state, the photon distribution of the output quantum light field corresponding to the two-mode harmonic oscillator presents a super-Poisson distribution, and the photons exhibit a strong anti-bunching effect. Using the three-dimensional discrete plot of the photon number distribution, the super-Poisson distribution and quantum dissipation effect of the output quantum state are intuitively demonstrated.<br>Finally, the SV entanglement criterion is used to determine that the output quantum state has a high degree of entanglement. Further numerical analysis shows that the degree of entanglement increases with the action time and the oscillator frequency.<br>In summary, the two-mode coupled harmonic oscillator constructed in this paper can be used to prepare highly entangled quantum states through a complete quantum dissipation process. This provides theoretical support for the experimental preparation of quantum entangled states based on dissipative mechanisms.

Effect of phase-sensitive manipulations on generation of low-frequency two-mode orthogonal squeezed vacuum states

<sec>Two-mode orthogonal squeezed vacuum states are an important quantum resource for quantum communication, quantum computing, quantum simulation, quantum precision measurement and sensing. It is essential to obtain stable two-mode orthogonal squeezed vacuum states in a low frequency range and compact configurations for practical applications, especially in quantum precision measurement and sensing. Two-mode orthogonal squeezed vacuum states are commonly produced via a subthreshold nondegenerate optical parametric amplifier (NOPA) in a continuous variable system. However, it is a difficult problem that the subthreshold NOPA cavity is phase sensitive manipulated to obtain stable squeezed vacuum states. Previous signal light injecting scheme relies on an injection of a weak light field into the subthreshold NOPA for phase sensitive manipulation. The injected signal light has the same frequency as the generated squeezed vacuum state. Thereby even the weakest injected signal light can introduce large amounts of excessive noise at low frequencies and the squeezing degree of two-mode squeezed vacuum states will be reduced or squeezing cannot be achieved.</sec><sec>In this paper, a single sideband frequency shifted light injecting scheme is proposed for phase sensitive manipulation of NOPA. The comparison between the single sideband frequency shifted light injecting scheme and the signal light injecting scheme for realization of phase sensitive manipulation of NOPA is conducted. The effects of the two schemes on the generation of the low-frequency two-mode orthogonal squeezed vacuum state light field are investigated experimentally . The experimental results show that in the signal light injecting scheme for phase sensitive manipulation, the squeezing degree of the two-mode orthogonal squeezed vacuum state continuously decreases until it disappears as the power of injected signal light increases. In the process of phase sensitive manipulation of NOPA by using the single sideband frequency shifted light injecting scheme, the squeezing degree of the two-mode orthogonal squeezed vacuum state does not change with the power of the injected frequency shifted light increasing. Stable phase sensitive manipulation is realized by injecting single sideband frequency shifted light into NOPA. The NOPA is operated in a phase sensitive amplification state for 30 min. Stable low-frequency two-mode orthogonal squeezed vacuum states are obtained. The (4.1 ± 0.1) dB amplitude orthogonal squeezed vacuum states and (4.0 ± 0.2) dB phase orthogonal squeezed vacuum states at a frequency of 200 kHz are generated stably, in a compact NOPA configuration.</sec>

Generalized sub-Poissonian states of two-beam fields.

Two-beam states obtained by partial photon-number-resolving detection in one beam of a multi-mode twin beam are experimentally investigated using an intensified CCD camera. In these states, sub-Poissonian photon-number distributions in one beam are accompanied by sub-shot-noise fluctuations in the photon-number difference of both beams. Multi-mode character of the twin beam implying the beam nearly Poissonian statistics is critical for reaching sub-Poissonian photon-number distributions, which contrasts with the use of a two-mode squeezed vacuum state. Relative intensities of both nonclassical effects as they depend on the generation conditions are investigated both theoretically and experimentally using photon-number distributions of these fields. Fano factor, noise-reduction parameter, local and global nonclassicality depths, degree of photon-number coherence, mutual entropy as a non-Gaussianity quantifier, and negative quasi-distributions of integrated intensities are used to characterize these fields. Spatial photon-pair correlations as means for improving the field properties are employed. These states are appealing for quantum metrology and imaging including the virtual-state entangled-photon spectroscopy.

Bound for Gaussian-state quantum illumination using a direct photon measurement.

It is important to find feasible measurement bounds for quantum information protocols. We present analytic bounds for quantum illumination with Gaussian states when using an on-off detection or a photon number resolving (PNR) detection, where its performance is evaluated with signal-to-noise ratio. First, for coincidence counting measurement, the best performance is given by the two-mode squeezed vacuum (TMSV) state which outperforms the coherent state and the classically correlated thermal (CCT) state. However, the coherent state can beat the TMSV state with increasing signal mean photon number in the case of the on-off detection. Second, the performance is enhanced by taking Fisher information approach with all counting probabilities including non-detection events. In the Fisher information approach, the TMSV state still presents the best performance but the CCT state can beat the TMSV state with increasing signal mean photon number in the case of the on-off detection. Furthermore, we show that it is useful to take the PNR detection on the signal mode and the on-off detection on the idler mode, which reaches similar performance of using PNR detection on both modes.

Steering witnesses for unknown Gaussian quantum states

We define and fully characterize the witnesses based on second moments detecting steering in Gaussian states by means of Gaussian measurements. All such tests, which arise from linear combination of variances or second moments of canonical operators, are easily implemented in experiments. We propose also a set of linear constraints fully characterizing steering witnesses when the steered party has one bosonic mode, while in the general case the constraints restrict the set of tests detecting steering. Given an unknown quantum state we implement a semidefinite program providing the appropriate steering test with respect to the number of random measurements performed. Thus, it is a ‘repeat-until-success’ method allowing for steering detection with less measurements than in full tomography. We study the efficiency of steering detection for two-mode squeezed vacuum states, for two-mode general unknown states, and for three-mode continuous variable GHZ states. In addition, we discuss the robustness of this method to statistical errors.

Enhanced entanglement and quantum teleportation of two-mode squeezed vacuum state via multistage non-Gaussian operations

The improvement of quantum features and processes, prominent as entanglement and quantum teleportation, of the two-mode squeezed vacuum state (TMSVS) in the small squeezed parameter domain is of great importance. Therefore, it has attracted the attention of scientists in the field of quantum information in recent years. In this paper, we introduce a new optical scheme to enhance the degree of entanglement and quantum teleportation fidelity of such a state using ordinary quantum devices including beam splitters and photon-number-resolving detectors. The scheme allows us to sequentially perform non-Gaussian operations, namely, photon addition, photon subtraction, quantum optical catalysis, and combinations of these techniques, into both modes of the TMSVS. The investigated results show that the degree of entanglement and fidelity in the novel two-mode non-Gaussian state is enhanced, especially in the small regions of the squeezed parameter compared with the original TMSVS and non-Gaussian states constructed from it in previous works. They also indicate that the enhanced zones recede to the small squeezed parameter areas with increasing the number of stages of the non-Gaussian effect.

How to verify identity in the continuous variable quantum system?

Continuous variable quantum cryptography has developed rapidly in recent decades, but how to verify identity in the continuous variable quantum system is still an urgent issue. To solve this problem, we propose a continuous variable quantum identification (CV-QI) protocol based on the correlation of the two-mode squeezed vacuum state and the continuous variable teleportation. The bidirectional identity verification between two participants of the communication can be achieved by the proposed CV-QI protocol. To guarantee the security, we make full use of the decoy state sequences during the whole process of the proposed CV-QI protocol. Besides, we provide the security analyses of the proposed CV-QI protocol, and analyses indicate that the security of the proposed CV-QI protocol is guaranteed.

Quantum loss sensing with two-mode squeezed vacuum state under noisy and lossy environment

We investigate quantum advantages in loss sensing when the two-mode squeezed vacuum state is used as a probe. Following an experimental demonstration in PRX 4, 011049, we consider a quantum scheme in which the signal mode is passed through the target and a thermal noise is introduced to the idler mode before they are measured. We consider two detection strategies of practical relevance: coincidence-counting and intensity-difference measurement, which are widely used in quantum sensing and imaging experiments. By computing the signal-to-noise ratio, we verify that quantum advantages persist even under strong thermal background noise, in comparison with the classical scheme which uses a single-mode coherent state that directly suffers from the thermal noise. Such robustness comes from the fact that the signal mode suffers from the thermal noise in the classical scheme, while in the quantum scheme, the idler mode does. For a fairer comparison, we further investigate a different setup in which the thermal noise is introduced to the signal mode in the quantum schemes. In this new setup, we show that the quantum advantages are significantly reduced. Remarkably, however, under an optimum measurement scheme associated with the quantum Fisher information, we show that the two-mode squeezed vacuum state does exhibit a quantum advantage over the entire range of the environmental noise and loss. We expect this work to serve as a guide for experimental demonstrations of quantum advantages in loss parameter sensing, which is subject to lossy and noisy environment.

Quantum repeater using two-mode squeezed states and atomic noiseless amplifiers

We perform a theoretical investigation into how a two-mode squeezed vacuum state, which has undergone photon loss, can be stored and purified using noiseless amplification with a collection of solid-state qubits. The proposed method may be used to probabilistically increase the entanglement between the two parties sharing the state. The proposed amplification step is similar in structure to a set of quantum scissors. However, in this work the amplification step is realized by a state transfer from an optical mode to a set of solid-state qubits, which act as a quantum memory. We explore two different applications, the generation of entangled many-qubit registers and the construction of quantum repeaters for long-distance quantum key distribution.

Unconditional remote entanglement using second-harmonic generation and twin two-mode squeezed vacuum states

We propose a photonics-based, continuous-variable (CV) form of remote entanglement utilizing strictly second-order nonlinear optical interactions that does not require the implementation of a state-projective measurement (i.e. remote entanglement without conditioning). This scheme makes use of two separate down-converters, wherein the corresponding nonlinear crystals are driven by strong classical fields as prescribed by the parametric approximation, as well as a fully quantum mechanical model of nondegenerate second harmonic generation (SHG) whose evolution is described by the trilinear Hamiltonian of the form $\hat{H}_{\text{shg}} = i\hbar\kappa\big(\hat{a}\hat{b}\hat{c}^{\dagger} - \hat{a}^{\dagger}\hat{b}^{\dagger}\hat{c}\big)$. By driving the SHG process with the signal modes of the two down-converters, we show entanglement formation between the generated second-harmonic mode (SH-mode) and the non-interacting joint-idler subsystem without the need for any state-reductive measurements on the interacting modes.