Phase-squeezed States Research Articles

Quantum-Limited Mirror-Motion Estimation

We experimentally demonstrate optomechanical motion and force measurements near the quantum precision limits set by the quantum Cramér-Rao bounds. Optical beams in coherent and phase-squeezed states are used to measure the motion of a mirror under an external stochastic force. Utilizing optical phase tracking and quantum smoothing techniques, we achieve position, momentum, and force estimation accuracies close to the quantum Cramér-Rao bounds with the coherent state, while the estimation using squeezed states shows clear quantum enhancements beyond the coherent-state bounds.

Dynamical generation of phase-squeezed states in two-component Bose-Einstein condensates

As an "input" state of a linear (Mach-Zehnder or Ramsey) interferometer, the phase-squeezed state proposed by Berry and Wiseman exhibits the best sensitivity approaching to the Heisenberg limit [Phys. Rev. Lett. 85, 5098 (2000)]. In this paper, we find that it can be generated dynamically with atomic Bose-Einstein condensates confined in a symmetric double well. Similar with the Berry and Wiseman's state, the prepared states show the squeezing along spin operator S_y and the anti-squeezing along S_z, leading to a sub-shot-noise of the phase sensitivity.

Chaos synchronization in a mutually coupled laser array subjected to self-mixing modulation

This tutorial presents a detailed description of experiments, simulations, and characterizations of chaos synchronization phenomena in the model of a mutually coupled microchip solid-state laser array subjected to self-mixing feedback modulation. We demonstrate a transition to synchronized chaos by the method of 'phase squeezing' with increasing field overlap between the two lasers. This phenomenon is well reproduced by numerical simulation of model equations. It is also shown that low energy variation as well as high disorder are concurrently established in synchronized chaos in the present system. The deterministic random switching (i.e., chaotic itinerancy) among phase-squeezed states and synchronized chaos states is numerically demonstrated in a transition region from a phase-squeezed state to a synchronized state. We characterize observed behaviours using such methods as singular value deposition (SVD), joint time–frequency analysis (JTFA) introducing a similarity function, and coarse-grained information transfer rate (CITR) analysis of long-term experimental or numerical time series, and discuss the physical significance of observed nonlinear dynamics in conjunction with chaos synchronization in mutually coupled lasers.

Characteristics of bright-squeezed light produced in a below-threshold optical parametric oscillator

We perform a theoretical analysis of steady-state solutions and quantum noise in a below-threshold optical parametric oscillator (OPO) operating as an amplifier with an input seed wave. Both the amplitude-squeezed and phase-squeezed states of the output field are considered. We take into account the intracavity nonlinear losses due to intracavity frequency doubling of the signal wave and the quantum fluctuations of the seed and pump waves. Unlike the preceding theoretical studies of the problem, we show that squeezing in bright beams produced by the OPO depends on their intensity. For the amplitude-squeezed state, squeezing strongly degrades with increasing output intensity. In contrast, one can obtain good squeezing for phase-squeezed beams of high output intensity.

Quantum phase distribution of thermal phase-squeezed states

The quantum phase distributions and variances of strong coherent and phase-squeezed states mixed with thermal light are calculated. We find that the effect of thermal light on the coherent phase distribution becomes important only when the number of thermal photons is of order one-half. Its effect on the phase distribution of phase-squeezed states (for the case where the number of photons is very large compared to ${e}^{2r})$ becomes important when the number of thermal photons is of order $\frac{1}{2}{e}^{\ensuremath{-}2r}$, where $r$ is the squeezing parameter.

NUMBER-PHASE SQUEEZED STATES AND PHOTON FRACTIONING

The number-phase squeezing mechanisms related to the multiphoton and photonfractioning procedures are analyzed. The main ingredients in these approaches are nonlinear multimode realizations of group-theoretical states and nonunitary subdynamics of the field modes. The states which are squeezed in the number of photons are suited to optical communications in local area networks; the states squeezed in the phase of the field optimize high-sensitive interferometry. Corresponding to the different kinds of squeezing and to the pertaining grouptheoretical states one has different types of amplifying devices with the same dynamical group of the states. In particular, two recently proposed devices – the photon-number amplifier (PNA) and the photon-number duplicator (PND) – attain both the multiphoton and photon-fractioning transformations. The PNA amplifies the field without degrading the direct-detection signal-to-noise ratio and thus can be used to produce number-squeezed states; the PND provides two copies of the same input number-state and, therefore, can connect two-mode states with one-mode states. Both the PNA and PND allow the realization of virtually lossless optical taps, which are essential in designing highly transparent local area networks. The PND can also be used in series with a conventional phase-insensitive amplifier to produce phase-squeezed states.

Generation of nonclassical photon states using correlated photon pairs and linear feedforward.

It is shown that nonclassical photon states can be produced by generating correlated photon pairs, measuring the idler mode, and manipulating the signal mode using feedforward and linear attenuators, amplifiers, or phase modulators. The minimum achievable Fano factor for such schemes is (2/\ensuremath{\pi}〈n〉${)}^{1/2}$, where 〈n〉 is the mean output photon number. A nondegenerate parametric oscillator followed by linear manipulators can reach this limit. A nondegenerate parametric amplifier followed by linear phase manipulation can produce phase-squeezed states. The minimum achievable phase noise is a factor 1/2G below that of a coherent state, where G is the amplifier gain. The advantages with these schemes are wavelength tunability, potentially very high squeezing bandwidth, and relative simplicity.