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Register a new userA novel two-mode squeezed light based on double-pump phase-matching
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A novel two-mode non-degenerate squeezed light is generated based on a four-wave mixing (4WM) process driven by two pump fields crossing at a small angle. By exchanging the roles of the pump beams and the probe and conjugate beams, we have demonstrated the frequency-degenerate two-mode squeezed light with separated spatial patterns. Different from a 4WM process driven by one pump field, the refractive index of the corresponding probe field $n_{p}$ can be converted to a value that is greater than $1$ or less than $1$ by an angle adjustment. In the new region with $n_{p}<1$, the bandwidth of the gain is relatively large due to the slow change in the refractive index with the two-photon detuning. As the bandwidth is important for the practical application of a quantum memory, the wide-bandwidth intensity-squeezed light fields provide new prospects for quantum memories.
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We propose Gaussian quantum illumination(QI) protocol exploiting asymmetrically squeezed two-mode(ASTM) state that is generated by applying single-mode squeezing operations on each mode of an initial two-mode squeezed vacuum(TMSV) state, in order to overcome the limited brightness of a TMSV state. We show that the performance of the optimal receiver is enhanced by local squeezing operation on a signal mode whereas the performance of a realistic receiver can be enhanced by local squeezing operations on both input modes. Under a fixed mean photon number of the signal mode, the ASTM state can be close to the TMSV state in the performance of QI while there is a threshold of beating classical illumination in the mean photon number of the initial TMSV state. We also verify that quantum discord cannot be a resource of quantum advantage in the Gaussian QI using the ASTM state, which is a counterexample of a previous claim.
A proposed phase-estimation protocol based on measuring the parity of a two-mode squeezed-vacuum state at the output of a Mach-Zehnder interferometer shows that the Cram{e}r-Rao sensitivity is sub-Heisenberg [Phys. Rev. Lett. {bf104}, 103602 (2010)]. However, these measurements are problematic, making it unclear if this sensitivity can be obtained with a finite number of measurements. This sensitivity is only for phase near zero, and in this region there is a problem with ambiguity because measurements cannot distinguish the sign of the phase. Here, we consider a finite number of parity measurements, and show that an adaptive technique gives a highly accurate phase estimate regardless of the phase. We show that the Heisenberg limit is reachable, where the number of trials needed for mean photon number $bar{n}=1$ is approximately one hundred. We show that the Cram{e}r-Rao sensitivity can be achieved approximately, and the estimation is unambiguous in the interval ($-pi/2, pi/2$).
We investigate the prospects of using two-mode intensity squeezed twin-beams, generated in Rb vapor, to improve the sensitivity of spectroscopic measurements by engaging two-photon Raman transitions. As a proof of principle demonstration, we demonstrated the quantum-enhanced measurements of the Rb $5D_{3/2}$ hyperfine structure with reduced requirements for the Raman pump laser power and Rb vapor number density.
We present a new technique for the detection of two-mode squeezed states of light that allows for a simple characterization of these quantum states. The usual detection scheme, based on heterodyne measurements, requires the use of a local oscillator with a frequency equal to the mean of the frequencies of the two modes of the squeezed field. As a result, unless the two modes are close in frequency, a high-frequency shot-noise-limited detection system is needed. We propose the use of a bichromatic field as the local oscillator in the heterodyne measurements. By the proper selection of the frequencies of the bichromatic field, it is possible to arbitrarily select the frequency around which the squeezing information is located, thus making it possible to use a low-bandwidth detection system and to move away from any excess noise present in the system.
The squeezed states of light become more and more important in the fields of quantum enhanced precision measurement and quantum information. To get this vital continuous variable quantum resource, the generation of squeezed states of light becomes a key factor. In this paper, a compact telecom fiber-based bright squeezed light (BSL) generator is demonstrated. To our knowledge, this is the first time that BSL has been reported in a fiber-based system to date. To obtain the BSL, a double-pass parametric amplifier based on surface-coated lithium niobate waveguide is employed. When the 1550 nm seed laser of the parametric amplifier is blocked, a stable 1.85 dB squeezed vacuum is obtained. With injected seed power of 80 {mu}W, an output power of 18 {mu}W and a squeezing value of 1.04 dB are achieved of the BSL at 1550 nm. Due to the good mode matching in the fiber and the absence of the resonant cavity, this flexible and compact BSL generator has the potential to be useful in out-of-the-laboratory quantum technologies. Moreover, the BSL has a narrow spectral width of 30 kHz, which is inherited from a narrow-linewidth single-frequency seed laser. In addition to being free from the wavelength-dependent losses, the narrowband BSL is also beneficial to improve the signal-to-noise ratio of quantum-enhanced precision measurement.
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