Low-light-level four-wave mixing by quantum interference

Ruseckas

Slow Light, Fast Light, and Opto-Atomic Precision Metrology IX

et al. 2016

Self Cite

Slow light based on the effect of electromagnetically induced transparency is of great interest due to its applications in low-light-level nonlinear optics and quantum information manipulation. The previous experiments all dealt with the single-component slow light. Here, we report the experimental demonstration of two-component or spinor slow light using a double-tripod atom-light coupling scheme. The scheme involves three atomic ground states coupled to two excited states by six light fields. The oscillation due to the interaction between the two components was observed. On the basis of the stored light, our data showed that the double-tripod scheme behaves like the two outcomes of an interferometer enabling precision measurements of frequency detuning. We experimentally demonstrated a possible application of the double-tripod scheme as quantum memory/rotator for the two-colour qubit. Our study also suggests that the spinor slow light is a better method than a widely used scheme in the nonlinear frequency conversion.

Section: Resultsmentioning

confidence: 99%

Experimental demonstration of spinor slow light

Ruseckas

Slow Light, Fast Light, and Opto-Atomic Precision Metrology IX

et al. 2016

Self Cite

“…To the best of our knowledge, this is the first observation of a CE exceeding 25% in the resonant double-Λ EIT scheme. According to the theoretical model, this resonant backward scheme can achieve 96% CE by using a medium with a large OD of 200, which reaches the same CE as the previous non-resonant scheme at half the OD 34 . Moreover, to compare the experimental data with the theoretical predictions, the phase-mismatch effect is included in the theoretical model, which was not considered in an earlier study of backward FWM 35 .…”

Section: Introductionmentioning

confidence: 77%

“…A simple method of suppressing spontaneous emission and thereby increasing the FWM efficiency in this forward double-Λ scheme is to shift the frequency of the applied laser field away from the resonant transition. Even though the interaction strength between light and matter is decreased in the non-resonant case, two research teams have demonstrated that the FWM efficiency can overcome the conversion limit (25%) of the resonant case 33 , 34 . Herein, we demonstrate that spontaneous emission can be effectively suppressed under a resonant condition only by arranging the applied laser beams in a backward configuration, which is the so-called backward FWM that was theoretically studied by Kang et al .…”

Section: Introductionmentioning

confidence: 99%

High-efficiency backward four-wave mixing by quantum interference

Liu

Xiao

Lin

et al. 2017

Sci Rep

Self Cite

Electromagnetically-induced-transparency-based four-wave mixing (FWM) in a resonant four-level double-Λ system has a maximum conversion efficiency (CE) of 25% due to spontaneous emission. Herein, we demonstrate that spontaneous emission can be considerably suppressed by arranging the applied laser beams in a backward configuration. With the backward double-Λ FWM scheme, we observe a CE of 63% in cold rubidium atoms with an optical depth (OD) of 48. To the best of our knowledge, this is the first observation of a CE exceeding the conversion limit in resonant FWM processes. Furthermore, we present a theoretical model that includes the phase-mismatch effect in the backward double-Λ FWM system. According to the theoretical model, the present scheme can achieve 96% CE using a medium with a large OD of 200 under ideal conditions. Such an efficient frequency conversion scheme has potential applications in optical quantum information technology.

“…The experimental data 11 NOVEMBER 2016 also show that the power of the transmitted light exceeds its input power in the double-Λ system. This light-amplification phenomenon is caused by the coherent light transfer between two N-type fourwave-mixing processes (j1i → j3i → j2i → j4i → j1i and j1i → j4i → j2i → j3i → j1i) [37]. More detailed discussions on the coherent light amplification can be found in the Supplemental Material [38].…”

Section: (B)mentioning

confidence: 99%

Optical Quantum Logic at the Ultimate Limit

Parkins

2016

Physics

We demonstrate an efficient cross-phase modulation (XPM) based on a closed-loop double-Λ system. The property of the double-Λ medium can be controlled by changing the phases of the applied optical fields. This phase-dependent XPM scheme can achieve large phase modulations at low-light intensities without requiring cavities or tightly focusing laser beams. With this scheme, we observe a π-level phase shift with two pulses, both consisting of eight photons in cold rubidium atoms. Such a novel scheme provides a simple route to generate strong interactions between photons and may have potential applications in all-optical quantum signal processing. DOI: 10.1103/PhysRevLett.117.203601 The realization of large cross-phase modulations (XPM) at low-light intensities, ultimately at the single-photon level, is an important but challenging task in quantum information science [1][2][3]. To reach this goal, one often requires high-finesse cavities to enhance nonlinear interactions between photons [4,5]. However, cavity-based experiments require many compromises such as balancing cavity bandwidth and light-matter coupling strength, which remain technical difficulties. Another promising approach for generating strong photon-photon interaction is electromagnetically induced transparency (EIT) [6][7][8], but according to the theoretical predictions by Harris and Hau, the cross-phase shift of the EIT-based Kerr medium in free space has an upper limit of order 0.1 radians at the singlephoton level [9]. To date, EIT-based XPM on the order of microradians per photon has been observed in cold atoms [10,11] and an Rb-filled fiber system [12]. In recent years, to overcome this upper limit there have been many theoretical proposals and experimental studies on this subject, including double slow-light schemes [13,14], stationary light schemes [15,16], cavity EIT schemes [17,18], or Rydberg EIT schemes [19][20][21][22][23][24][25]. Very recently, two research teams have overcome this upper limit and observed single-photon cross-phase shifts of π=3 and π by using cavity EIT [26] and Rydberg EIT [27], respectively. This is great progress toward implementing a photon-photon gate.Here, we report an experimental observation of a novel XPM scheme based on a phase-dependent double-Λ system. With this scheme, we observe a large cross-phase shift of 3.6 AE 1.0 radians induced by a light pulse containing around eight photons in cold rubidium atoms. This XPM scheme does not require cavities or Rydberg atoms, which provides a simple route to generate strong interactions between photons and obtain large cross-phase shifts per photon.In the present study, we investigate a closed-loop double-Λ XPM in a laser-cooled 87 Rb atomic system, as depicted in Fig. 1(a). Cold atomic gas with an optical depth of approximately 50 is produced in a dark spontaneous-force optical trap [28]. A strong coupling field (Ω c denotes its Rabi frequency) drives the j2i ↔ j3i transition to create a transparent medium for a weak probe pulse (Ω p , j1i ↔ j3i) through quantum ...