Photon Subtraction at Hybrid Interferometer Output Enhances Phase Estimation, Mitigating up to 20% Photon Loss

Precise phase estimation lies at the heart of many quantum technologies, and researchers continually seek methods to surpass fundamental limits on accuracy. Qisi Zhou, Tao Jiang, and Qingqian Kang, alongside colleagues including Teng Zhao, Xin Su, and Cunjin Liu, now demonstrate a significant advance in this field. They propose a novel approach using photon subtraction at the output of a hybrid interferometer, a device combining an optical amplifier and beam splitter, to overcome the limitations imposed by unavoidable photon loss. This technique markedly improves phase sensitivity, boosts the signal-to-noise ratio, and importantly, allows for measurements that exceed the standard Heisenberg limit, even when substantial photon loss occurs, paving the way for more robust and accurate quantum devices.

The hybrid interferometer, integrating an optical parametric amplifier and a beam splitter, offers performance exceeding that of conventional SU(1,1) interferometers. To overcome photon loss, a significant challenge for practical implementation, the researchers propose a quantum metrology scheme utilizing multi-photon subtraction. This approach enhances the precision of phase estimation by reducing the impact of photon loss, demonstrating substantial improvements achievable with careful implementation. This work introduces a novel strategy for enhancing quantum metrology protocols and advancing the development of high-precision measurement technologies.

Employing coherent and vacuum states as inputs, alongside a variable beam splitter, enhances robustness against photon loss. The results show that the choice of input modes significantly affects phase estimation, and optimizing the beam splitter’s transmittance is crucial for maximizing phase sensitivity in lossy conditions. Photon subtraction markedly improves phase sensitivity, quantum Fisher information, and robustness against noise, achieving sensitivities beyond the Heisenberg limit even with 20% photon loss.

Optimized Phase Estimation in Noisy Environments

This research develops a theoretical framework for achieving the ultimate precision limit in phase estimation using quantum-enhanced metrology, explicitly accounting for noise. The core idea is to use a specific type of interferometer and optimize the measurement strategy to minimize the impact of noise on the phase estimation precision. The calculations determine the quantum Fisher information, the minimum achievable precision, and the impact of noise. Key concepts include quantum metrology, phase estimation, quantum Fisher information, and the SU(1,1) interferometer. Squeezed states, non-classical states of light, are used to improve precision, and the calculations maximize the quantum Fisher information while accounting for noise. The research utilizes the density matrix to describe the quantum state and calculates partial derivatives to determine the quantum Fisher information, optimizing interferometer parameters to maximize the quantum Fisher information and minimize precision.

Hybrid Interferometer Surpasses Quantum Limit with Loss

This research demonstrates a hybrid interferometer capable of surpassing the standard quantum limit, known as the Heisenberg limit, for phase estimation even with significant photon loss. By integrating an optical parametric amplifier with a variable beam splitter and employing a multi-photon subtraction scheme, the team achieved enhanced sensitivity and robustness against noise. The study reveals that careful selection of input states, specifically coherent and vacuum states, plays a crucial role in optimizing phase estimation performance, and adjusting the transmittance of the variable beam splitter proves essential for maximizing sensitivity, particularly in conditions with substantial photon loss. The team’s approach successfully mitigates the detrimental effects of photon loss, a common limitation in practical interferometers, allowing for precision measurements beyond conventional boundaries. Results indicate that the proposed scheme not only improves phase sensitivity and Fisher information but also enhances robustness against noise, maintaining high performance even when up to 20% of photons are lost. This work establishes a promising pathway for developing highly sensitive and robust interferometers for applications in quantum metrology and precision sensing.