Coherent Control of Single-Photon Absorption and Reemission in a Two-Level Atomic Ensemble

Abstract

We demonstrate coherent control of single-photon absorption and reemission in a two-level cold atomic ensemble. This is achieved by interfering the incident single-photon wave packet with the emission (or scattering) wave. For a photon with an exponential growth waveform with a time constant equal to the excited-state lifetime, we observe that the single-photon emission probability during the absorption can be suppressed due to the perfect destructive interference. After the incident photon waveform is switched off, the absorbed photon is then reemitted to the same spatial mode as that of the incident photon with an efficiency of 20%. For a photon with an exponential decay waveform with the same time constant, both the absorption and reemission occur within the waveform duration. Our experimental results suggest that the absorption and emission of a single photon in a two-level atomic ensemble may possibly be manipulated by shaping its waveform in the time domain. DOI: 10.1103/PhysRevLett.109.263601 PACS numbers: 42.50.Nn, 03.65.Ta, 32.80.Qk, 42.50.Ct Photon absorption and emission are two key probes to study the light-matter quantum interaction, which lays down the foundations for atomic, molecular, and optical physics [1][2][3]. When a coherent optical pulse propagates through a medium, the absorption and emission can coherently modify its spectral components and lead to many interesting and important optical phenomena, such as attenuation, amplification, distortion, and slow and fast light effects [4][5][6][7][8]. For a single photon, causality requires that the absorption and reemission follow the right time order: the reemission can only occur following the absorption. Although this quantum time order has been observed as the antibunching effect in resonance fluorescence measured by two-photon correlations [9,10], it is not controllable on demand in these experiments. When a single photon enters a two-level atomic medium, the absorption and emission usually both occur within the photon pulse duration. Recently, Scully et al. proposed a scheme for observing directed ''spontaneous'' emission excited by a single photon [11].In this Letter, we demonstrate coherent control of singlephoton absorption and reemission in a two-level cold atomic ensemble in free space by shaping the singlephoton waveform. Making use of the destructive interference between the emission (or scattering) and the incident photon wave packet, we show that the probability of reemitting the photon during the absorption can be completely suppressed when the incident photon has an exponential growth waveform with a time constant equal to the excitedstate lifetime. The reemission process only starts after the incident photon waveform is switched off and thus can be controlled on demand. This technique can be used to efficiently excite atoms with a given single atom. Our result may have potential applications in the quantum networks that require efficient conversion between flying single-photon states and local atomic states [12]. Figure 1 i...

Efficient coupling to an optical resonator by exploiting time-reversal symmetry

“…In recent experiments, time-reversal techniques were successfully applied to demonstrate a high absorption probability of a single photon by an atomic ensemble [15]. The benefit of pulse shaping in the case of single atoms and multi-photon pulses was demonstrated in [16].…”

Measuring the Biphoton Temporal Wave Function with Polarization-Dependent and Time-Resolved Two-Photon Interference

“…Using spontaneous four-wave mixing (SFWM) in cold atoms [20], the sub-MHz biphoton generation with a coherence time on the order of microseconds has been demonstrated [21][22][23]. Such a long coherence time of single photons allows manipulating their temporal waveforms [24][25][26] and their interaction with atoms in the time domain [27][28][29]. Owning to the nanosecond time resolution of commercially available single-photon counting modules (SPCM), the biphoton amplitude temporal profile can be directly measured from the coincidence counts.…”

Time reversal of arbitrary photonic temporal modes via nonlinear optical frequency conversion

“…For example, the temporal shape emitted by a single quantum emitter (atom, quantum dot, etc) in free space is not the shape that leads to efficient absorption by a receiving quantum absorber, even if the emitter and absorber are physically identical. For efficient absorption, the envelope of the emitted wave packet must be time reversed [1][2][3]. Optimal input and output modes of optical cavities have a similar time-reversed relationship [4,5], as has been demonstrated experimentally for weak classical pulses [6] and for single-photon wave packets [7].…”