Abstract The scheme of an arrangement is considered for the preparation of some non-classical superposed states from squeezed states by using the optical parametric amplifier (OPA) apparatus, which is based on an idea recently proposed to generate photon-added states from the coherent states of light. This technique allows one to obtain linear combinations of squeezed vacuum states (SVSs) and n-photon-added squeezed vacuum states (n-PASVSs), that can enrich the non-classicality of the SVSs and n-PASVSs and improve their performances in quantum information protocols. Their characteristics are greatly affected by the gain of the OPA and the coherent field amplitude (or, mean number of photons). For this purpose, a comprehensive analysis of the non-classical features of these states has been presented in four different behavioral regimes, i.e. low- and high-gain regimes in the presence of weak and strong coherent fields. Finally, the role of the gain parameter of the light state from OPA as one of the input states of the Mach–Zehnder interferometer (MZI) apparatus in phase sensitivity optimization is discussed.
Abstract The scheme of an arrangement is considered for the preparation of some non-classical superposed states from squeezed states by using the optical parametric amplifier (OPA) apparatus, which is based on an idea recently proposed to generate photon-added states from the coherent states of light. This technique allows one to obtain linear combinations of squeezed vacuum states (SVSs) and n-photon-added squeezed vacuum states (n-PASVSs), that can enrich the non-classicality of the SVSs and n-PASVSs and improve their performances in quantum information protocols. Their characteristics are greatly affected by the gain of the OPA and the coherent field amplitude (or, mean number of photons). For this purpose, a comprehensive analysis of the non-classical features of these states has been presented in four different behavioral regimes, i.e. low- and high-gain regimes in the presence of weak and strong coherent fields. Finally, the role of the gain parameter of the light state from OPA as one of the input states of the Mach–Zehnder interferometer (MZI) apparatus in phase sensitivity optimization is discussed.
Abstract Recently, photon subtraction from the single-mode squeezed vacuum state (SVS) has been explored as a technique to enhance its squeezing strength (SS). Notably, the enhancement is observed only when an even number of photons is subtracted, and this effect is limited to a specific range of the squeezing parameter r. In this paper, we introduce a novel class of single-mode nonclassical states, termed as qubit superposed SVSs (qSSVSs), via the coherent superposition of a SVS and a single-photon-subtracted SVS. The primary objective of this work is to enhance the SS for any r > 0 through the creation of these superposed states. Our analysis reveals that the qSSVSs not only improve the SS but also exhibit enhanced nonclassical features such as the negativity of Wigner function, single-mode antibunching effect, photon-number distribution, and sub-Poissonian photon statistics. Furthermore, we demonstrate that the qSSVSs provide superior phase sensitivity in a quantum Mach–Zehnder interferometer compared to the original SVS. Importantly, the generation of qSSVSs is feasible using readily available optical devices, including a beam splitter, a photodetector, and an amplitude displacement. These states hold significant potential for practical applications in quantum information science, particularly for tasks such as information encoding and processing in quantum computing systems.
The heralded optical parametric amplifier (OPA) has emerged as a promising tool for quantum state engineering. However, its potential has been limited to coherent state inputs. Here, we introduce a generalized heralded OPA protocol that unlocks a vastly expanded class of quantum phenomena by accepting arbitrary non-classical inputs. With a squeezed vacuum input, the setup functions as an integrated two-photon subtractor, deterministically generating high-fidelity, larger-amplitude squeezed Schrödinger cat states -- an operation previously requiring complex, discrete setups. Furthermore, when fed a small-amplitude SC state, the protocol acts as a non-Gaussianity amplifier, distilling it into high-purity approximations of key quantum resources like specific photon-number superpositions. This work transforms the OPA from a specialized source into a versatile and practical platform for advanced quantum state engineering, enabling the generation of a wide array of non-Gaussian states from a single, integrated setup.
We propose a multiphoton heralding scheme using an optical parametric amplifier (OPA) that converts squeezed vacuum into two families of non-Gaussian states: large-amplitude squeezed Schrödinger cat states and low-order parity-selective Fock superpositions. By injecting m photons into the idler port and detecting n photons at the output, effective high-order photon subtraction is realized in a single OPA device. The heralded states exhibit strong Wigner negativity and high phase-space complexity. Remarkably, under photon loss, the complexity remains substantial even after negativity vanishes, indicating a loss-resilient quantum resource. These states also surpass the Heisenberg limit in phase estimation. Our protocol establishes the OPA as a versatile platform for generating non-Gaussian states, with promising applications in loss-resilient quantum metrology and fault-tolerant quantum information processing.
Abstract This paper investigates the quantum features of non-Gaussian states generated by applying a two-mode squeezing operator S ˆ a b ( s ) to two generalized single-mode squeezed vacuum states (SVSs), each formed by the superposition of an SVS and a single–photon–subtracted SVS. The results show that, in the new states, the two-mode squeezing effect, the Einstein–Podolsky–Rosen (EPR) correlation, the Hillery–Zubairy entanglement, and the linear entropy are all enhanced as the two-mode squeezing parameter s increases. Moreover, both the degrees of squeezing and entanglement are improved and exceed those of the two-mode squeezed vacuum state (TMSVS) for stronger single-mode squeezing parameters. The optimal conditions for achieving such enhancements are identified for different regimes, depending on whether the generalized SVSs are purely Gaussian, maximally non-Gaussian, or intermediate states. In an application, the quantum Cramér–Rao bound (QCRB) is evaluated when the non-Gaussian states are employed as inputs to a Mach–Zehnder interferometer (MZI). The results further demonstrate that the enhanced phase sensitivity in the MZI originates from both the squeezing strengths and the intrinsic photon-subtraction operation. These findings highlight the potential of the new non-Gaussian states as promising resources for quantum metrology and quantum sensing.
Quantum Cramer-Rao (QCR) bound is attached to a particular nonclassical state, therefore appropriate choice of the probe state is of the key importance to enhance sensitivity beyond classical one. Since the work of C.M. Caves (Phys. Rev. D 23 1693 (1981)) Mach-Zehnder (MZ) interferometry operates with single-mode squeezed vacuum (SMSV) light coupled with a coherent state. We report the gain sensitivity of the phase-dependent MZ interferometer by more than 10 dB compared to the original result (Phys. Rev. Lett. 100, 073601 (2008)) by using SMSV state with squeezing <10 dB from which a certain number of photons was initially subtracted. The gain sensitivity is also observed when measuring the difference of output intensities of the SMSV state with squeezing <3 dB from which 2,4,6 photons are subtracted and large coherent state. Overall, subtracting photons from the initially weakly squeezed light can prove to be a more efficient strategy in the quantum MZ interferometry compared to highly squeezed SMSV state generation.
Abstract Choice of the quantum probe state is of key importance to enhance the sensitivity of the Mach–Zehnder (MZ) interferometer beyond the classical one and even approach the quantum Cramér–Rao bound. According to the work of Caves (Caves 1981 Phys. Rev. D 23 1693), the quantum MZ interferometer is a phase-dependent one operating with single-mode squeezed vacuum (SMSV) light coupled with a coherent state. We use the SMSV state with squeezing <10 dB and report a gain in sensitivity of the phase-dependent MZ interferometer of more than 10 dB compared to the original result (Pezze and Smerzi 2008 Phys. Rev. Lett. 100 073601) via photon subtraction. The gain in sensitivity is also observed when measuring the difference in output intensities of the SMSV state with squeezing of < 3 dB from which two, four, and six photons are subtracted and a large coherent state. Overall, subtracting photons from the initially weakly squeezed light can prove to be a more efficient strategy in quantum MZ interferometry compared to highly squeezed SMSV state generation.