Quantum metrology harnesses nonclassical resources including squeezed states and quantum entanglement to overcome fundamental limitations imposed by the shot-noise limit (SNL). While conventional optical interferometers for phase detection typically operate in the MHz-frequency regime due to technical noise constraints at lower frequencies, numerous practical applications demand operation in the kHz regime or below. Here, we present a truncated SU(1,1) interferometric configuration that achieves enhanced phase sensitivity in the low-frequency (kHz) domain by exploiting quantum entanglement generated through two-mode squeezed states. Our approach incorporates quantum sideband control to achieve quantum correlations across multiple low-frequency bands while simultaneously suppressing technical noise. Through precise locking of optimal phase, we demonstrate a significant improvement in signal-to-noise ratio within the kHz range, with phase sensitivity surpassing the SNL by 2.0 ± 0.2 dB. These experimental results provide crucial validation for extending entanglement-enhanced optical interferometry into low-frequency metrological applications and establish novel methodologies for optical modulation and sideband-based quantum information processing and quantum sensing protocols.
Quantum metrology harnesses nonclassical resources including squeezed states and quantum entanglement to overcome fundamental limitations imposed by the shot-noise limit (SNL). While conventional optical interferometers for phase detection typically operate in the MHz-frequency regime due to technical noise constraints at lower frequencies, numerous practical applications demand operation in the kHz regime or below. Here, we present a truncated SU(1,1) interferometric configuration that achieves enhanced phase sensitivity in the low-frequency (kHz) domain by exploiting quantum entanglement generated through two-mode squeezed states. Our approach incorporates quantum sideband control to achieve quantum correlations across multiple low-frequency bands while simultaneously suppressing technical noise. Through precise locking of optimal phase, we demonstrate a significant improvement in signal-to-noise ratio within the kHz range, with phase sensitivity surpassing the SNL by 2.0 ± 0.2 dB. These experimental results provide crucial validation for extending entanglement-enhanced optical interferometry into low-frequency metrological applications and establish novel methodologies for optical modulation and sideband-based quantum information processing and quantum sensing protocols.
We propose and experimentally demonstrate a quantum-enhanced fiber Mach-Zehnder interferometer for low-frequency phase measurement beyond the shot-noise limit using a high-frequency squeezing technique. The local oscillator field is amplitude-modulated in the MHz range and is then demodulated to avoid the technical noise that occurs at low frequencies. After measurement of the phase noise at a frequency of tens of kHz, an improvement of ∼2 dB relative to the shot-noise level is achieved. Additionally, the amplitude modulation depth has no significant effect on the phase noise improvement of the interferometer when deployed in our experimental configuration. The current scheme introduces a quantum technique into the fiber-based measurements, particularly for the low frequency range, and this scheme has potential applications in the high-precision fiber sensing of temperature, strain, and various other parameters.
In recent years, distributed quantum sensing has gained interest for a range of applications requiring networks of sensors, from global-scale clock synchronization to high energy physics. In particular, a network of entangled sensors can improve not only the sensitivity beyond the shot noise limit, but also enable a Heisenberg scaling with the number of sensors. Here, using bright entangled twin beams, we theoretically and experimentally demonstrate the detection of a linear combination of two distributed phases beyond the shot noise limit with a truncated SU(1,1) interferometer. Specifically, we show a quantum noise reduction of 1.7 ± 0.3 dB below what is possible with the corresponding classical configuration. Additionally, we theoretically extend the use of a truncated SU(1,1) interferometer to a multi-phase-distributed sensing scheme that leverages entanglement as a resource to achieve a quantum improvement in the scaling with the number of sensors in the network. Our results pave the way for developing quantum-enhanced sensor networks that can achieve an entanglement-enhanced sensitivity.
Quantum interferometric sensing plays a crucial role in a wide range of applications, including quantum metrology, quantum imaging, and quantum lithography, where minute phase shifts carry valuable physical information. The strength of quantum sensing lies in surpassing classical sensitivity limits, particularly through the use of quantum correlations and squeezing to suppress optical shot noise. Birefringence sensing is crucial for various applications, as it provides detailed information about the material's structure, stress, composition, and environmental conditions. We present an interferometric scheme for detecting unknown small birefringence beyond the shot-noise limit of sensitivity that leverages the hyper-squeezing (squeezed in both number-phase and polarization correlations) within a pair of polarized nonlinear SU(1,1) interferometers, coupled by the birefringence. Specifically, two pairs of crossed-polarization nonlinear media, both generate and measure two-mode quantum light that is squeezed and polarization-entangled. We present a complete theoretical analysis of the interferometer's sensitivity to small birefringence under realistic conditions of gain and internal loss, illuminating the potential for enhancement of the sensitivity by 3-15dB in practical, real-world experiments (the exact achievable enhancement is governed solely by the loss).
Introducing squeezed states of light into interferometers can increase the phase sensitivity of the device beyond the standard quantum limit (SQL). We discuss an SU(1,1) interferometer, where nonlinear optical elements replace the beam splitters in a Mach-Zehnder interferometer. A two-mode squeezed state of light is generated inside of such an interferometer. We talk about the phase sensitivities of an SU(1,1) interferometer with different detection schemes and their improvement over the SQL. We also discuss the concept of an optimal detection scheme for phase measurement in an interferometer. We describe a modification of the SU(1,1) interferometer which reduces the experimental complexities while giving the same phase sensitivity. We call the design a truncated SU(1,1) interferometer. We show our experimental results of 4 dB improvement in phase sensitivity over the SQL using a truncated SU(1,1) interferometer. We also compare the theoretical sensitivities of vacuum-seeded configurations of a conventional and a truncated SU(1,1) interferometer, and show our experimental results for the phase sensitivity of the truncated version. We explain the dependence of phase sensitivity on the measurement of squeezing. We talk about the methods to improve the measurement of squeezing in a 4-wave mixing experiment, and our efforts in implementing them. Finally, we mention our progress in measuring a big phase shift using an adaptive algorithm in the truncated SU(1,1) interferometer, and discuss the technicalities involved in big phase measurements.
In this manuscript, we discuss the performance of a recently demonstrated polarization-based truncated SU(1,1) interferometer1 which can potentially generate polarization-entangled twin beams for applications in quantum communications or in quantum metrology as an interferometer with enhanced phase sensitivity. Using the intensity-squeezed twin beams generated via four-wave mixing (FWM) in hot Rubidium vapor, we report the detection of nearly -2 dB of noise reduction below the shot-noise in the joint-quadrature measurements in such interferometer. We also used this setup to confirms the non-classical nature of quantum correlations between the twin beams with an inseparability parameter I = 1:32±0:04 that falls below the classical limit of 2. One of the important advantages of the proposed interferometer is its better rejection of common-mode, technical, and environmental noises due to its intrinsic symmetry, which allows for squeezing and entanglement measurements at wide spectrum of detection frequencies from as low as 200 Hz (limited by 1=f electronic noise) to up to a few MHz (limited by the photodetector gain bandwidth).
Homodyne detection is often used for interferometers based on nonlinear optical gain media. For the configuration of a seeded, "truncated SU(1,1)" interferometer Anderson, et al. [ Phys. Rev. A95, 063843 (2017)] showed how to optimize the homodyne detection scheme and demonstrated theoretically that it can saturate the quantum Cramer-Rao bound for phase estimation. In this work we extend those results by taking into account loss in the truncated SU(1,1) interferometer and determining the optimized homodyne detection scheme for phase measurement. Further, we build a truncated SU(1,1) interferometer and experimentally demonstrate that this optimized scheme achieves a reduction in noise level, corresponding to an enhanced potential phase sensitivity, compared to a typical homodyne detection scheme for a two-mode squeezed state. In doing so, we also demonstrate an improvement in the degree to which we can beat the standard quantum limit with this device.