Abstract Quantum squeezing, which makes measurement sensitivity beyond classical limit by reducing system noise, is an essential non-classical resource for quantum metrology. It is of great importance to enhance quantum squeezing since the squeezing degree directly determines the extent to which measurement sensitivity beats the classical limit. Recently, a two-mode phase-sensitive amplifier has been utilized to enhance the quantum squeezing of phase-insensitive amplifier. However, such enhancement has an intrinsic limit of 3 dB. Here we show that such limit of 3 dB can be overcome by utilizing multi-beam interference. Specifically, a quantum squeezing enhancement of about 3.67 dB is observed by direct measurement. Moreover, we find that the amount of quantum squeezing enhancement increases as the number of multi-beam interference increases, which clearly shows that beating the quantum squeezing enhancement limit of 3 dB is induced by multi-beam interference. Our results here provide an efficient way to enhance the quantum squeezing.
Spin squeezing is vitally important in quantum metrology and quantum information science. The noise reduction resulting from spin squeezing can surpass the standard quantum limit and even reach the Heisenberg limit (HL) in some special circumstances. However, systems that can reach the HL are very limited. Here, we study the spin squeezing in atomic systems with a generic form of the quadratic collective-spin interaction, which can be described by the Lipkin-Meshkov-Glick model. We find that the squeezing properties are determined by the initial states and the anisotropic parameters. Moreover, we propose a pulse rotation scheme to transform the model into a two-axis twisting model with Heisenberg-limited spin squeezing. Our study paves the way for reaching HL in a broad variety of systems.
Squeezed states of light enable enhanced measurement precision by reducing noise below the standard quantum limit. A key application of squeezed light is nonlinear microscopy, where state-of-the-art performance is limited by photodamage and quantum-limited noise. Such microscopes require bright, pulsed light for optimal operation, yet generating and detecting bright pulsed squeezing at high levels remains challenging. In this work, we present an efficient technique to generate high levels of bright picosecond pulsed squeezed light using a
χ2 optical parametric amplification process in a waveguide. We measure
−3.2 dB of bright squeezing with optical power compatible with nonlinear microscopy, as well as
−3.6 dB of vacuum squeezing. Corrected for losses, these squeezing levels correspond to
−15.4−8.7+2.7 dB of squeezing generated in the waveguide. The measured level of bright amplitude pulsed squeezing is to our knowledge the highest reported to date, and will contribute to the broader adoption of quantum-enhanced nonlinear microscopy in biological studies.
The quantum speed limit time for quantum system under squeezed environment is studied. We consider two typical models, the damped Jaynes–Cummings model and the dephasing model. For the damped Jaynes–Cummings model under squeezed environment, we find that the quantum speed limit time becomes larger with the squeezed parameter r increasing and indicates symmetry about the phase parameter value θ = π. Meanwhile, the quantum speed limit time can also be influenced by the coupling strength between the system and environment. However, the quantum speed limit time for the dephasing model is determined by the dephasing rate and the boundary of acceleration region that interacting with vacuum reservoir can be broken when the squeezed environment parameters are appropriately chosen.