Twin-beam intensity-difference squeezing below 10 Hz

Abstract

We report the generation of strong, bright-beam intensity-difference squeezing down to measurement frequencies below 10 Hz. We generate two-mode squeezing in a four-wave mixing (4WM) process in Rb vapor, where the single-pass-gain nonlinear process does not require cavity locking and only relies on passive stability. We use diode laser technology and several techniques, including dual seeding, to remove the noise introduced by seeding the 4WM process as well as the background noise. Twin-beam intensity-difference squeezing down to frequencies limited only by the mechanical and atmospheric stability of the lab is achieved. These results should enable important low-frequency applications such as direct intensity-difference imaging with bright beams on integrating detectors.

Two-beam Coupling in the Production of Quantum Correlated Images by Four-wave Mixing

“…We find that the issue can be avoided either with sufficiently low power (in both the probe input seed and the output amplified probe -as was the situation in Ref. [10] where this complication did not appear) or by seeding with beams that do not directly intersect in the gain medium.…”

“…The 2-beam coupling was not observed, for instance, in Ref. [10], where very low seed intensities were used, so that the coupling, even at the output, was never very large. The 2-beam coupling effect only happens when the two seed beams interact with the same atoms.…”

“…The experimental setup that we use to demonstrate the 2-beam coupling in the squeezed light generation (Fig. 1 (a)) is almost identical to the setup used to demonstrate low-frequency squeezed light [10]. We use a Ti:sapphire laser as the basis for these experiments because of its superior noise properties in these experiments in comparison to most diode lasers.…”

“…Experiments have shown that for typical pump laser intensities and detunings the squeezing bandwidths in these systems typically extend up to about 20 MHz, the cut-off depending on the intensity of the pump laser [9]. The low-frequency cut-off of the squeezing has been in the kHz range, but recent advances have succeeded in obtaining low-frequency squeezing to about 10 Hz using a dual-seeding technique (balancing two seeded beams and their conjugates on the detectors) [10]. This has now opened up the possibility of extending this technology to imaging applications.…”

Quantum Conformance Test

“…is the mean photon number, and |n⟩ i is the n-photon state in the i = S signal, or i = I idler mode. TMSV states can easily be produced experimentally by spontaneous parametric down-conversion (SPDC) (36)(37)(38) or four-wave mixing (39,40,41). A multimode TMSV state is a tensor product of K TMSV states ⊗ K |⟩.…”