The “quantum Radar” seeks to harness quantum entanglement and squeezing to improve the detection of faint targets beyond the best possible classical sensor. The major challenge of the quantum Radar is the very large optical loss of the target beam, which induces vacuum fluctuations and hampers the quantum correlation. In addition, the faint target reflection requires the use of high power beams, which favors high-power stimulated sources of coherent squeezed light over spontaneous low power sources of entangled photons. I will present the lossy SU1,1 nonlinear interferometer with coherent seeding as a candidate for quantum Radar sensing. I will highlight the quantum features of this sensor and report a demonstration of the quantum enhanced interference contrast, even in the presence of high loss.
The sensitivity of coherent Raman spectroscopy methods such as Stimulated Raman Spectroscopy (SRS) or Coherent Anti-Stokes Raman Spectroscopy (CARS), is ultimately limited by shot noise from the stimulating fields. We present sub-shot-noise and background-free squeezed-light Raman spectroscopy, where the resonant Raman gain of the sample is enhanced by the quantum squeezing of two parametric amplifiers, while the nonresonant background of the Raman response in the sample is eliminated by destructive interference. Our configuration incorporates the Raman sample between two parametric amplifiers that squeeze the light in orthogonal quadrature axes (forming a nonlinear SU(1,1) interferometer), where the presence of a resonant Raman response induces a nonlinear phase shift, which can be measured below the shot-noise limit due to the squeezed illumination. Seeding the interferometer with coherent input further increases the Raman signal, similar to classical coherent methods. Thus, this method gains the benefits of both the coherent (classical) amplification of the seed and the squeezing-enhanced (quantum) sub-shot-noise sensitivity.
High repetition rate mode-locked lasers (in the GHz range), are desired for frequency comb spectroscopy. A major obstacle that currently impedes high repetition mode-locking is the inevitable subsequent reduction of the single pulse energy, which reduces the efficiency of the nonlinear Kerr effect in the cavity, eventually precluding mode-locking. The standard methods to overcome this restriction is to try to maintain the intra-cavity peak intensity in spite of the reduction of the single pulse energy, by tightening the focus of the intra-cavity beam on the crystal, or by enhancing the output coupler reflectivity and increasing the pump power. This standard approach is however limited since these actions also provide better conditions for CW operation, which reduces the ML robustness, and eventually spurs the laser to operate in CW. We demonstrate a fresh attack on this problem: instead of aiming to preserve the peak intensity by tightening the focus and lowering the OC loss, we enhance the nonlinearity inside the cavity to compensate for the reduction in intra-cavity peak intensity. We harness the enhanced nonlinearity to specifically target the intra-cavity peak intensity and explore its limits and effects. With an additional nonlinear window in the cavity we enhanced the Kerr nonlinearity by an order on magnitude compared to the standard Ti:S, allowing to maintain mode-locking with an output coupler reflectivity as low as R=55% and record-low intra-cavity peak intensity (10GW/cm2, 50 times less than without enhanced non-linearity). Our results provide an important new knob for high-repetition rate mode-locking.
Conference Committee Involvement (2)
Quantum Computing, Communication, and Simulation V
25 January 2025 | San Francisco, California, United States
Quantum Computing, Communication, and Simulation IV
27 January 2024 | San Francisco, California, United States
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