Kristin Beck

All-Optical Switch and Transistor Gated by One Stored Photon

A Single-Photon Gate A long-standing goal in optics is to produce an all-optical transistor, in which the transmission of a light beam can be controlled by a single photon. Using a system in which a cloud of cesium atoms is coupled to an optical cavity, Chen et al. (p. 768, published online 4 July; see the Perspective by Volz and Rauschenbeutel) were able to control transmission through the optical cavity by exciting the atomic ensemble using a “gate” laser pulse. Just one gate photon stored was sufficient to detune the system and switch the transmission of source photons through the cavity. Optical transmission through a cesium-filled cavity can be controlled by a single stored photon. [Also see Perspective by Volz and Rauschenbeutel] The realization of an all-optical transistor, in which one “gate” photon controls a “source” light beam, is a long-standing goal in optics. By stopping a light pulse in an atomic ensemble contained inside an optical resonator, we realized a device in which one stored gate photon controls the resonator transmission of subsequently applied source photons. A weak gate pulse induces bimodal transmission distribution, corresponding to zero and one gate photons. One stored gate photon produces fivefold source attenuation and can be retrieved from the atomic ensemble after switching more than one source photon. Without retrieval, one stored gate photon can switch several hundred source photons. With improved storage and retrieval efficiency, our work may enable various new applications, including photonic quantum gates and deterministic multiphoton entanglement.

Large conditional single-photon cross-phase modulation.

Significance Strong, coherent interactions between individual photons can revolutionize communication and computation technology. An interaction between two photons that changes their relative phase by 180° could serve as the basis for universal quantum logic. Realizing such interaction, however, has been a grand experimental challenge. We use atoms trapped between high-reflectivity mirrors to make two individual photons interact strongly with each other. We demonstrate that the phase of a light wave can be changed by up to 60° by a single light quanta. With today’s technology, this approach may enable the realization of deterministic quantum gates. Deterministic optical quantum logic requires a nonlinear quantum process that alters the phase of a quantum optical state by π through interaction with only one photon. Here, we demonstrate a large conditional cross-phase modulation between a signal field, stored inside an atomic quantum memory, and a control photon that traverses a high-finesse optical cavity containing the atomic memory. This approach avoids fundamental limitations associated with multimode effects for traveling optical photons. We measure a conditional cross-phase shift of π/6 (and up to π/3 by postselection on photons that remain in the system longer than average) between the retrieved signal and control photons, and confirm deterministic entanglement between the signal and control modes by extracting a positive concurrence. By upgrading to a state-of-the-art cavity, our system can reach a coherent phase shift of π at low loss, enabling deterministic and universal photonic quantum logic.

One-dimensional array of ion chains coupled to an optical cavity

We present a novel system where an optical cavity is integrated with amicrofabricatedplanar-electrode iontrap.The trapelectrodesproduceatunable periodic potential allowing the trapping of up to 50 separate ion chains aligned with the cavity and spaced by 160µm in a one-dimensional array along the cavity axis. Each chain can contain up to 20 individually addressable Yb + ions coupled to the cavity mode. We demonstrate deterministic distribution of ions between the sites of the electrostatic periodic potential and control of the ion-cavity coupling. The measured strength of this coupling should allow access to the strong collective coupling regime with .10 ions. The optical cavity could serve as a quantum information bus between ions or be used to generate a strong wavelength-scale periodic optical potential.

Partially Nondestructive Continuous Detection of Individual Traveling Optical Photons.

We report the continuous and partially nondestructive measurement of optical photons. For a weak light pulse traveling through a slow-light optical medium (signal), the associated atomic-excitation component is detected by another light beam (probe) with the aid of an optical cavity. We observe strong correlations of g_{sp}^{(2)}=4.4(5) between the transmitted signal and probe photons. The observed (intrinsic) conditional nondestructive quantum efficiency ranges between 13% and 1% (65% and 5%) for a signal transmission range of 2% to 35%, at a typical time resolution of 2.5  μs. The maximal observed (intrinsic) device nondestructive quantum efficiency, defined as the product of the conditional nondestructive quantum efficiency and the signal transmission, is 0.5% (2.4%). The normalized cross-correlation function violates the Cauchy-Schwarz inequality, confirming the nonclassical character of the correlations.

Nondestructive Detection of Traveling Optical Photons in Real Time

We nondestructively observe individual optical photons in real time as they propagate through a slow-light medium. The nondestructive measurement is accomplished with another light that detects the atomic-excitation component of the slow photons.