Spatial interference of macroscopic light fields from independent Raman sources

Extracting the phase information from atomic memory by intensity correlation measurement

We demonstrate experimentally controlled storage and retrieval of the optical phase information in a higher-order interference scheme based on Raman process in (87)Rb atomic vapor cells. An interference pattern is observed in intensity correlation measurement between the write Stokes field and the delayed read Stokes field as the phase of the Raman write field is scanned. This result implies that the phase information of the Raman write field can be written into the atomic spin wave via Raman process in a high gain regime and subsequently read out via a spin-wave enhanced Raman process, thus achieving optical storage of phase information. This technique should find applications in optical phase image storage, holography and information processing.

Quantum random bit generation using energy fluctuations in stimulated Raman scattering

Random number sequences are a critical resource in modern information processing systems, with applications in cryptography, numerical simulation, and data sampling. We introduce a quantum random number generator based on the measurement of pulse energy quantum fluctuations in Stokes light generated by spontaneously-initiated stimulated Raman scattering. Bright Stokes pulse energy fluctuations up to five times the mean energy are measured with fast photodiodes and converted to unbiased random binary strings. Since the pulse energy is a continuous variable, multiple bits can be extracted from a single measurement. Our approach can be generalized to a wide range of Raman active materials; here we demonstrate a prototype using the optical phonon line in bulk diamond.

Quantum random bit generation using stimulated Raman scattering

Random number sequences are a critical resource in a wide variety of information systems, including applications in cryptography, simulation, and data sampling. We introduce a quantum random number generator based on the phase measurement of Stokes light generated by amplification of zero-point vacuum fluctuations using stimulated Raman scattering. This is an example of quantum noise amplification using the most noise-free process possible: near unitary quantum evolution. The use of phase offers robustness to classical pump noise and the ability to generate multiple bits per measurement. The Stokes light is generated with high intensity and as a result, fast detectors with high signal-to-noise ratios can be used for measurement, eliminating the need for single-photon sensitive devices. The demonstrated implementation uses optical phonons in bulk diamond.

Observation of coherence between two independent atomic ensembles by Raman scattering

By using spontaneous Raman processes in the high-gain regime, we create instantaneous coherence between two independent atomic ensembles. The coherence is confirmed by the observation of temporal beating between the two subsequent readout fields converted from the atomic excitations through another enhanced Raman process. The beat frequency is found to be a result of an AC Stark frequency shift effect. We find that, due to the spontaneous nature of the process, the phases of the two ensembles change from one realization to another even though there is good coherence for a single realization.

Quantum-fluctuation-initiated coherence in multioctave Raman optical frequency combs

We show experimentally and theoretically that the spectral components of a multioctave frequency comb spontaneously created by stimulated Raman scattering in a hydrogen-filled hollow-core photonic crystal fiber exhibit strong self-coherence and mutual coherence within each 12 ns driving laser pulse. This coherence arises in spite of the field's initiation being from quantum zero-point fluctuations, which causes each spectral component to show large phase and energy fluctuations. This points to the possibility of an optical frequency comb with nonclassical correlations between all comb lines.

High-contrast interference pattern of amplified spontaneous emission from dyes under transient grating excitation

We demonstrate a high-contrast interference fringe pattern formed by amplified spontaneous emission (ASE) in a noncollinear two-beam self-diffraction setup by use of dyes. In the presence of a transient grating a stable interference pattern is observed in ASE induced by one- and two-photon absorption. The fringe visibility varies from 0.2 to 0.65 with a temporal delay in the two beams. The variation of the angle between the two exciting beams at the temporal overlap shows an increase in the fringe visibility with an increase in the angle.