Squeezing-enhanced Raman spectroscopy

Abstract

The sensitivity of classical Raman spectroscopy methods, such as coherent anti-stokes Raman spectroscopy (CARS) or stimulated Raman spectroscopy (SRS), is ultimately limited by shot-noise from the stimulating fields. We present the complete theoretical analysis of a squeezing-enhanced version of Raman spectroscopy that overcomes the shot-noise limit of sensitivity with enhancement of the Raman signal and inherent background suppression, while remaining fully compatible with standard Raman spectroscopy methods. By incorporating the Raman sample between two phase-sensitive parametric amplifiers that squeeze the light along orthogonal quadrature axes, the typical intensity measurement of the Raman response is converted into a quantumlimited, super-sensitive estimation of phase. The resonant Raman response in the sample induces a phase shift to signal-idler frequency-pairs within the fingerprint spectrum of the molecule, resulting in amplification of the resonant Raman signal by the squeezing factor of the parametric amplifiers, whereas the non-resonant background is annihilated by destructive interference. Seeding the interferometer with classical coherent light stimulates the Raman signal further without increasing the background, effectively forming squeezing-enhanced versions of CARS and SRS, where the quantum enhancement is achieved on top of the classical stimulation.

Optimal Scheme for Quantum Metrology

“…Metrology, which studies the precision limit of measurement and estimation, plays a central role in science and technology. Recently quantum metrology, which exploits quantum mechanical effects to achieve far better precision than classical schemes , has gained increasing attention and has found wide applications in various fields, such as gravitational wavedetection [19,[23][24][25][26][27], quantum phase estimation [5,[28][29][30][31], quantum magnetometer [32,33], quantum ranging [34][35][36], quantum spectroscopy [37][38][39][40], quantum imaging [41][42][43][44][45][46][47], quantum target-detection [48,49], quantum gyroscope [50,51], distributed quantum sensing [52][53][54], atomic clocksynchronization [55][56][57][58][59][60][61], and even biological measurements [62].…”

Magneto Optical Sensing beyond the Shot Noise Limit

“…Caves showed that squeezed states of light enable sensitivity beyond the SNL in interferometric measurements 8 . Thirty years later, squeezed light is now an important resource for quantum sensing for a wide range of applications [9][10][11] , with examples ranging from gravitational wave detection 12,13 to plasmonic sensing 11,[14][15][16] to scanning probe microscopies 9,17,18 , magnetometry [19][20][21][22] , Raman spectroscopy [23][24][25] , and spin noise spectroscopy 26,27 . Nonlinear interferometry, in which beamsplitters are replaced with nonlinear amplifiers, has also drawn interest in recent years as an alternative to conventional quantum sensing with squeezed states [28][29][30][31] .…”

Augmenting the Sensing Performance of Entangled Photon Pairs through Asymmetry

“…OPA is set to a higher gain for broadband parametric homodyne measurement [31,32] and overcoming detection loss [33][34][35], etc. In addition to direct phase sensing, The improved signal-to-noise due to the squeezing was also harnessed for various other applications, such as Raman spectroscopy [36,37] and atomic force microscopy [38]. The SU(1,1) interferometer can operate in multiple regimes, depending on the intensity of the fields: quantum or classical [39], spontaneous or stimulated [40,41], with optical losses shown to degrade the squeezing [42][43][44].…”