We demonstrate a quantum critical sensing platform using a biased degenerate optical parametric oscillator. Through weak, phase-controlled coherent displacements to intracavity field, we show exponential precision scaling with system size.
Quantum metrology, a cornerstone of quantum technologies, exploits entanglement and superposition to achieve higher precision than classical protocols in parameter-estimation tasks. When combined with critical phenomena such as phase transitions, the divergence of quantum fluctuations is predicted to enhance the performance of quantum sensors. Here, we implement a critical quantum sensor using a superconducting parametric (i.e., two-photon driven) Kerr resonator. The sensor, a linear resonator terminated by a superconducting quantum interference device, operates near the critical point of a finite-component second-order dissipative phase transition obtained by scaling the system parameters. We analyze the performance of a frequency-estimation protocol and show that quadratic precision scaling with respect to the system size can be achieved with finite values of the Kerr nonlinearity. Since each photon emitted from the cavity carries more information about the parameter to be estimated compared to its classical counterpart, our protocol opens up perspectives for faster or more precise metrological protocols. Our results demonstrate that quantum advantage in a sensing protocol can be achieved by exploiting a phase transition.
We propose and experimentally demonstrate a method to study intracavity quantum states and their dynamics in an optical parametric oscillator (OPO). By measuring the OPO steady state’s sensitivity to an external bias field, we show how intracavity quantum states can be reconstructed. Our method includes precise control over the pump phase, facilitating arbitrary quadrature reconstruction and enabling complete visualization of cavity states using Husimi Q-function representations. We experimentally demonstrate the quantum tomography of an intracavity squeezed vacuum state generated by an OPO pumped below threshold. Additionally, by controlling the bias time delay and amplitude relative to the pump it allows for the reconstruction of the intracavity state at various times, offering insights into the temporal evolution of the OPO intracavity state. This approach provides a powerful tool for exploring and understanding the intricate behavior of quantum states within optical cavities.
Quantum criticality has received extensive attention due to its ability to significantly enhance quantum sensing. But its realization and control in many-body quantum systems remain challenging. We present an effective scheme to simulate the Lipkin-Meshkov-Glick (LMG) model using a coherent Ising machine (CIM) composed of a network of degenerate optical parametric oscillators (DOPO). In our work, the spin variables of the LMG model are mapped onto the phases of DOPO pulses, and the spin-spin interactions are realized by all-to-all couplings among them. Through our investigation of the critical behavior in the antiferromagnetically coupled LMG model in the thermodynamic limit, i.e., N→∞, and its application in quantum sensing near the critical point, we verify that the CIM does not only effectively capture the second-order quantum phase transition (QPT) at the critical point but also reconstructs its complete phase diagram under ferromagnetic coupling. Furthermore, we demonstrate how the critical dynamics of this simulation platform can be utilized for quantum-enhanced metrology, achieving a measurement precision that diverges near the critical point of the LMG model. These results highlight the capability of the CIM as a flexible experimental platform for investigating the QPT in the fundamental quantum magnetic models, providing valuable insights into quantum simulation and critical phenomena.