Difference Squeezing Research Articles

NONCLASSICAL PROPERTIES OF TWO-MODE DISPLACED FOCK STATE

In this paper, we investigate a variety of nonclassical properties of a two-mode displaced Fock state (TMDFS). Nonclassical properties such as sum squeezing, difference squeezing, antibunching effect, and the Cauchy-Schwarz inequality will be discussed analytically for the TMDFS. The results show that by changing the Fock state parameters between modes and the displacement parameter, the TMDFS exhibits enhanced nonclassical behaviors and makes a valuable contribution to quantum optics.

Multichannel Six‐Wave Mixing with Spatial Multimode and Squeezing via Atomic Coherence

AbstractMultimode properties, based on nonlinear parametric processes, have potential research value on entanglement imaging. This paper studies the spatial and frequency multimode from dressing parametric‐amplified six‐wave mixing (PA‐SWM) process with three entangled signals. The S1 signal contains fifth‐order nonlinearity, the S2 signal contains electromagnetically induced absorption and fifth‐order nonlinearity, and the S3 signal contains Autler–Townes splitting (AT), second‐ and fifth‐order nonlinearity. The frequency multimode is attributed to dressing energy level splitting in spontaneous SWM (SSWM) process. The spatial multimode is due to frequency multimode and beam splitting via Kerr nonlinearity. In the spatial domain, it finds the optimal conditions of intensity difference squeezing (IDS) and spatial imaging along with their competitive relationship. On the one hand, the light spots with single spatial mode are contributed to the maximum IDS but not conducive to entanglement imaging; on the other hand, the light spots with multiple spatial modes are instrumental in entanglement imaging but not appropriate for the IDS. This research has potential applications in squeezed light sources for quantum metrology, and correlated imaging of spatial signals.

Enhanced intensity difference squeezing with a low gain off-resonant Four-Wave Mixing in potassium vapor

Although potassium stands out among alkalies by its smallest ground state hyperfine splitting, smaller than Doppler broadening, investigations of its four-wave mixing (FWM) quantum properties, like squeezing and entanglement, were neglected. Here we present measurements of quantum correlations in potassium vapor using far-detuned double Λ scheme for FWM. We obtained the relative intensity difference squeezing (IDS) of -6.1 dB, with the squeezing bandwidth between 0.9 to 4.5 MHz on the noise spectra. The squeezing maximum in potassium compares well with the best results obtained in Rb and Cs, and has larger value than previously reported IDS in potassium. This result agrees qualitatively well with the squeezing calculated using analytical expressions from the model of operators when with chosen parameters FWM generates both squeezing and probe at their maximums. The ultimate squeezing level in potassium, predicted by the model, when conjugate absorption in the cell and optical losses behind the cell are neglected, is −10.29 dB. This is among the largest predicting squeezing obtained by FWM in alkalies.

Difference Squeezing in Degenerate Three-Photon Absorption Six-Wave Interaction Process

: In this paper, difference squeezing in the degenerate three-photon absorption six-wave interaction process is examined. The difference squeezing in fields between the pump and Stokes modes can be converted to normal squeezing in the signal mode, and vice versa. It is demonstrated that in the pump mode, amplitude-cubed squeezing is directly turned into normal squeezing in the signal mode. The squeezing in the stimulated interaction, which reduces the depth of classicality of the field amplitude, is seen to be larger than the corresponding squeezing in the spontaneous interaction, despite having the same number of pump photons. Difference squeezing is observable only in certain domain values of pump photons. It is deduced that the multi-photon absorption nonlinear optical approach is the best way to generate optimal squeezed laser light in any optical system.

Generation of plasmon-polaritons in epsilon-near-zero polaritonic metamaterial

In this paper, we study some non-classical properties and propose the generation schemes of the superposition of multiple-photon-added two-mode squeezed vacuum state (SMPA-TMSVS). Based on the Wigner function, we clarify that this state is a non-Gaussian state, while the original two-mode squeezed vacuum state (TMSVS) is a Gaussian state. Besides, the SMPA-TMSVS is sum squeezing, as well as difference squeezing. In particular, the manifestation of the sum squeezing and the difference squeezing in the SMPA-TMSVS becomes more pronounced when increasing parameters r and e. In addition, by exploiting the schemes of photon-added superposition in the usual order, we give some schemes that the SMPA-TMSVS can be generated with the higher-order photon-added superposition by using some optical devices.

Non-classical properties and generation schemes of superposition of multiple-photon-added two-mode squeezed vacuum state

In this paper, we study some non-classical properties and propose the generation schemes of the superposition of multiple-photon-added two-mode squeezed vacuum state (SMPA-TMSVS). Based on the Wigner function, we clarify that this state is a non-Gaussian state, while the original two-mode squeezed vacuum state (TMSVS) is a Gaussian state. Besides, the SMPA-TMSVS is sum squeezing, as well as difference squeezing. In particular, the manifestation of the sum squeezing and the difference squeezing in the SMPA-TMSVS becomes more pronounced when increasing parameters r and e. In addition, by exploiting the schemes of photon-added superposition in the usual order, we give some schemes that the SMPA-TMSVS can be generated with the higher-order photon-added superposition by using some optical devices.

Squeezing in the Difference of the Fields in Degenerate Four-and Five-wave Interaction Processes

Squeezing in the difference of the fields in degenerate four- and five-wave interaction processes is studied. It is shown that the difference squeezing can be led to normal squeezing of the field for uncorrelated modes. It is found that the amplitude-squared squeezing of the fundamental mode directly converted into the normal squeezing of the signal mode in the four-wave interaction process and amplitude-cubed of the fundamental directly converted into the normal squeezing of the signal mode in the five-wave interaction process. Detection of higher-order squeezing in these processes is also studied. It is observed that difference squeezing responds nonlinearly to the number of pump photons and found greater in the stimulated process than in spontaneous one. Difference squeezing exists only in certain domain value of pump photons. It is inferred that the multi-photon absorption process is more suitable for the generation of optimum squeezed light.

Broadband quadrature-squeezed vacuum and nonclassical photon number correlations from a nanophotonic device

We report demonstrations of both quadrature-squeezed vacuum and photon number difference squeezing generated in an integrated nanophotonic device. Squeezed light is generated via strongly driven spontaneous four-wave mixing below threshold in silicon nitride microring resonators. The generated light is characterized with both homodyne detection and direct measurements of photon statistics using photon number-resolving transition-edge sensors. We measure 1.0(1) decibels of broadband quadrature squeezing (~4 decibels inferred on-chip) and 1.5(3) decibels of photon number difference squeezing (~7 decibels inferred on-chip). Nearly single temporal mode operation is achieved, with measured raw unheralded second-order correlations g (2) as high as 1.95(1). Multiphoton events of over 10 photons are directly detected with rates exceeding any previous quantum optical demonstration using integrated nanophotonics. These results will have an enabling impact on scaling continuous variable quantum technology.

Quantum Noise Correlations of an Optical Parametric Oscillator Based on a Nondegenerate Four Wave Mixing Process in Hot Alkali Atoms.

We present the first measurement of two-mode squeezing between the twin beams produced by a doubly resonant optical parameter oscillator (OPO) in an above threshold operation based on parametric amplification by nondegenerate four wave mixing with rubidium (^{85}Rb). We demonstrate a maximum intensity difference squeezing of -2.7 dB (-3.5 dB corrected for losses) with a pump power of 285mW and an output power of 12mW for each beam, operating close to the D1 line of Rb atoms. The use of open cavities combined with the high gain media can provide a strong level of noise compression and the access to new operation regimes that could not be explored by crystal based OPOs. The spectral bandwidth of the squeezed light is broadened by the cavity dynamics, and the squeezing level is robust for strong pump powers. Stable operation was obtained up to 4 times above the threshold. Moreover, operation of the OPO close to the atomic resonances of alkali atoms allows a natural integration into quantum networks, including structures such as quantum memories.

Enhanced squeezing of four-wave mixing by phase-sensitive dressed effect in a hot atomic system

In this paper, we demonstrate that the intensity difference squeezing (IDS) of parametric amplified four-wave mixing (PA-FWM) can be modulated by the phase-sensitive dressed effect in a hot rubidium (Rb) atomic system. The introduction of phase-sensitive dressed effect can enhance the degree of IDS of PA-FWM to −8.1 dB, as compared to that in the phase-insensitive dressed PA-FWM of −6.6 dB. The phase-sensitive dressing field can not only enhance the degree of IDS of PA-FWM by the dressed effect, but can also be treated as the seed beam of the PA-six wave mixing process. So, double-injected three-mode IDS obviously has a bigger degree of IDS compared with the single-injection case. One advantage of the current scheme for enhancing the generated IDS is that the experimental setup is simple and mechanically stable. These outcomes can be used in the fabrication of quantum devices and the realization of quantum metrology.

Modulation gain and squeezing by dressed state in hot atomic system

We report that the optical gain and intensity difference squeezing (IDS) of four-wave mixing can be controlled using an external dressing field in a hot rubidium atomic system. The intensity of the parametric amplified four-wave mixing (PA-FWM) signal in the probe and corresponding conjugate channels can be enhanced using the dressed effect, resulting in an increase of the optical gain. So, the IDS in the dressed PA-FWM has a higher degree of −7.1 dB, as compared to that in the PA-FWM of −2.5 dB. This scheme of enhancing the optical gain and the generated IDS requires a simple experimental setup that is mechanically stable. These outcomes can be used in the fabrication of quantum devices and the realization of quantum metrology.

Quantum Zeno effect and nonclassicality in a PT -symmetric system of coupled cavities

The interplay between the nonclassical features and the parity-time (PT) symmetry (or its breaking) is studied here by considering a PT symmetric system consisting of two cavities with gain and loss. The conditions for PT invariance is obtained for this system. The behavior of the average photon number corresponding to the gain and loss modes for different initial states (e.g., vacuum, NOON, coherent, and thermal states) has also been obtained. With the help of the number operators, quantum Zeno and anti-Zeno effects are studied, and the observed behavior is compared in PT symmetric (PTS) and PT symmetry broken (PTSB) regimes. It has been observed that the relative phase of the input coherent fields plays a key role in the occurrence of these effects. Further, some nonclassicality features are witnessed using criteria based on the number operator(s). Specifically, intermodal antibunching, sum and difference squeezing, are investigated for specific input states. It is found that the various nonclassical features, including the observed quantum Zeno and anti-Zeno effects, are suppressed when one goes from PTS to PTSB regime. In other words, the dominance of the loss/gain rate in the field modes over the coupling strength between them diminishes the nonclassical features of the system.

Long-distance distribution of the telecom band intensity difference squeezing generated in a fiber optical parametric amplifier.

Using an all-fiber source of pulsed twin beams, with the record intensity difference squeezing of 6.1±0.15 dB for fiber optical parametric amplifiers, we experimentally distribute the pulsed continuous variable (CV) quantum state over a long distance. After separating the signal and idler twin beams by 26km single-mode fibers, the measured intensity difference noise is still below the shot noise limit by 2dB. The result shows that the distribution process is only affected by the vacuum noise originated from the fiber transmission loss. The extra noise contributed by the acoustic wave Brillouin scattering and Raman scattering in 26km transmission fibers has not been observed. The investigation is beneficial for studying long-distance CV quantum communication.

Difference squeezing of the optical fields in degenerate six-wave interaction process

Difference squeezing of the optical fields in degenerate six-wave interaction process

Phase-sensitive cascaded four-wave-mixing processes for generating three quantum correlated beams

Theoretical studies and experimental implementations of quantum correlation are the important contents of continuous variables quantum optics and quantum information science. There are various systems for the study of quantum correlation. Here, we study an experimental scheme for generating three quantum correlated beams based on phase-sensitive cascaded four-wave-mixing (FWM) processes in rubidium vapor. Quantum correlation including intensity difference or sum squeezing, two other combinatorial squeezing, and quantum entanglement among the three output light fields are theoretically analyzed in this paper. Also, the comparison of the quantum correlations have been made between the phase-sensitive cascaded FWM processes and the phase-insensitive cascaded FWM processes. By changing the phases and intensities of the input beams, it is interesting to find that the maximum degrees of various combinatorial squeezing are equal when the two FWM processes share a common intensity gain. When the common intensity gain of the two FWM processes changes, the maximum degrees of different combinatorial squeezing will be synchronously controlled. At last we discuss the genuine tripartite entanglement and steering in our phase-sensitive cascaded scheme, and compare them with the cases of the phase-insensitive cascaded scheme.

Robust and compact entanglement generation from diode-laser-pumped four-wave mixing

Four-wave-mixing processes are now routinely used to demonstrate multi-spatial-mode Einstein-Podolsky-Rosen entanglement and intensity difference squeezing. Diode-laser-pumped four-wave mixing processes have recently been shown to provide an affordable, compact, and stable source for intensity difference squeezing, but it was unknown if excess phase noise present in power amplifier pump configurations would be an impediment to achieving quadrature entanglement. Here, we demonstrate the operating regimes under which these systems are capable of producing entanglement and under which excess phase noise produced by the amplifier contaminates the output state. We show that Einstein-Podolsky-Rosen entanglement in two mode squeezed states can be generated by a four-wave-mixing source deriving both the pump field and the local oscillators from a tapered-amplifier diode-laser. This robust continuous variable entanglement source is highly scalable and amenable to miniaturization, making it a critical step toward the development of integrated quantum sensors and scalable quantum information processors, such as spatial comb cluster states.

Quantum frequency up-conversion of continuous variable entangled states

We demonstrate experimentally quantum frequency up-conversion of a continuous variable entangled optical field via sum-frequency-generation process. The two-color entangled state initially entangled at 806 and 1518 nm with an amplitude quadrature difference squeezing of 3.2 dB and phase quadrature sum squeezing of 3.1 dB is converted to a new entangled state at 530 and 1518 nm with the amplitude quadrature difference squeezing of 1.7 dB and phase quadrature sum squeezing of 1.8 dB. Our implementation enables the observation of entanglement between two light fields spanning approximately 1.5 octaves in optical frequency. The presented scheme is robust to the excess amplitude and phase noises of the pump field, making it a practical building block for quantum information processing and communication networks.

Higher nonclassical properties and entanglement of photon-added two-mode squeezed coherent states

We investigate how photon addition operations affect some higher-order nonclassical properties and the intermodal entanglement of a non-Gaussian entangled state generated by adding photons to both modes of a two-mode squeezed coherent state (TMSCS). We show that the photon addition operation can enhance the degrees of the sum squeezing and the difference squeezing for appropriate combinations of several parameters involved in the TMSCS. We consider the existing Hillery-Zubairy entanglement criterion, and find that the quantity of Hillery-Zubairy E gets more negative not only for a larger value of the squeezing parameter r but also for greater values of photon addition numbers (m, n). Our results may imply that the highest enhancement is obtained when same number of operations (i.e., m=n) is applied to both modes. However, for the photon-added TMSCS (PA-TMSCS), the more violation to the Hillery-Zubairy inequality does not necessarily following strong sum squeezing and difference squeezing. This because their behaviors with three phases and squeezing parameter r involved in the TMSCS are somewhat different.

Quantum engineering and nonclassical properties of SU(1,1) and SU(2) entangled nonlinear coherent states

In this paper, after a brief review on the entangled coherent state, a general form of the entangled nonlinear coherent state has been introduced based on the nonlinear coherent states approach. By choosing particular f-deformation functions, theoretical schemes for generation of two distinct classes of such states associated with SU(1,1) and SU(2) groups are presented. The entanglement characteristic of the corresponding entangled coherent states has been studied by evaluating the concurrence. In the continuation, other nonclassical behaviors of the produced states have been analyzed by investigating sub-Poissonian photon statistics, the oscillatory photon number distribution, one- and two-mode quadrature squeezing, and sum and difference squeezing. Accordingly, in addition to their entanglement property, other nonclassicality features of the introduced states are well established in detail.

Parametric amplification of dressed multi-wave mixing in an atomic ensemble

We theoretically investigate the influence of a dressing field on parametric amplification multi-wave mixing (PA-MWM) processes in an atomic ensemble for the first time. The quantum spatial properties of PA-MWM signals are demonstrated by studying the cone emissions. Meanwhile, we investigate the intensities, the intensity difference squeezing, and the intensity noise correlation of bright twin PA-MWM beams, which are generated by injecting the MWM signals into the input ports of a spontaneous parametric four-wave mixing process. Both the spatial properties and the quantum correlation can be enhanced or suppressed via a bright state or a dark state, which is induced by the single or double dressing effect. This study has potential applications in quantum security, quantum imaging and long distance quantum communications.