Compact source of Einstein-Podolsky-Rosen entanglement and squeezing at very low noise frequencies

Abstract

We report on the experimental demonstration of strong quadrature Einstein-Podolsky-Rosen entanglement and squeezing at very low noise sideband frequencies produced by a single type-II, self-phase-locked, frequency degenerate optical parametric oscillator below threshold. The generated two-mode squeezed vacuum state is preserved for noise frequencies as low as 50 kHz. Designing simple setups able to generate nonclassical states of light in the kHz regime is a key challenge for high sensitivity detection of ultraweak physical effects such as gravitational wave or small beam displacement.

High-fidelity single-photon source based on a Type II optical parametric oscillator

“…1. A continuous-wave frequency-doubled Nd:YAG laser (Diabolo, Innolight) pumps below threshold a triply-resonant OPO made of a semimonolithic linear cavity [17]. The input mirror is directly coated on one face of a 10 mmlong KTP crystal (Raicol), with an intensity reflection of 95% for the 532 nm pump and high reflection at 1064 nm.…”

Photothermal fluctuations as a fundamental limit to low-frequency squeezing in a degenerate optical parametric oscillator

“…Θ (11) in /Θ (13) in is the amplitude noise coupling constant of the seed/pump field, Θ (12) in /Θ (14) in is the phase noise coupling constant of the seed/pump field, and the rest of the Θ's are the amplitude and phase noise coupling constants of the vacuum fields at the fundamental and second-harmonic frequencies. Note that the normalized quadrature variances are completely characterized by the normalized quadrature variances of the two input and vacuum fields and the coupling constants.…”

“…For such states the squeezing bandwidth should cover the GW detection band (10Hz to 10kHz). Several results have been published below 300kHz [12,13,14] with the lowest result 280Hz [11]. These frequencies represent a different regime experimentally to the majority of squeezed state production and as such other potential limiting low frequency noise sources need to be considered.…”

Squeezed light at sideband frequencies below 100 kHz from a single OPA

“…The absence of a laser beam at the (fundamental) reference frequency doesnÕt provide length control of the OPO cavity, nor can phase modulation sidebands be therefrom induced to accompany the vacuum squeezed states. In [16] locked vacuum squeezing down to 50 kHz has been demonstrated using the second harmonic laser beam for OPO cavity length control and a noise dither locking technique for quadrature angle control at the homodyne detector. In [17] squeezing at 200 Hz has been demonstrated; their system also used a noise dither locking technique, the OPO length was not controlled.…”

“…During the refereeing process two new experiments were performed demonstrating squeezed light at even lower frequencies [16,17]. In both systems optical parametric oscillators (OPOs) were applied.…”