M. D. Eisaman

Electromagnetically induced transparency with tunable single-photon pulses

Techniques to facilitate controlled interactions between single photons and atoms are now being actively explored. These techniques are important for the practical realization of quantum networks, in which multiple memory nodes that utilize atoms for generation, storage and processing of quantum states are connected by single-photon transmission in optical fibres. One promising avenue for the realization of quantum networks involves the manipulation of quantum pulses of light in optically dense atomic ensembles using electromagnetically induced transparency (EIT, refs 8, 9). EIT is a coherent control technique that is widely used for controlling the propagation of classical, multi-photon light pulses in applications such as efficient nonlinear optics. Here we demonstrate the use of EIT for the controllable generation, transmission and storage of single photons with tunable frequency, timing and bandwidth. We study the interaction of single photons produced in a ‘source’ ensemble of 87Rb atoms at room temperature with another ‘target’ ensemble. This allows us to simultaneously probe the spectral and quantum statistical properties of narrow-bandwidth single-photon pulses, revealing that their quantum nature is preserved under EIT propagation and storage. We measure the time delay associated with the reduced group velocity of the single-photon pulses and report observations of their storage and retrieval.

Shaping quantum pulses of light via coherent atomic memory.

We describe proof-of-principle experiments demonstrating a novel approach for generating pulses of light with controllable photon numbers, propagation direction, timing, and pulse shapes. The approach is based on preparation of an atomic ensemble in a state with a desired number of atomic spin excitations, which is later converted into a photon pulse. Spatiotemporal control over the pulses is obtained by exploiting long-lived coherent memory for photon states and Electromagnetically Induced Transparency in an optically dense atomic medium. Using photon counting experiments, we observe Electromagnetically Induced Transparency based generation and shaping of few-photon sub-Poissonian light pulses.

Quantum control of light using electromagnetically induced transparency

We present an overview of recent theoretical and experimental work on the control of the propagation and quantum properties of light using electromagnetically induced transparency in atomic ensembles. Specifically, we discuss techniques for the generation and storage of few-photon quantum-mechanical states of light as well as novel approaches to manipulate weak pulses of light via enhanced nonlinear optical processes.

GENERATION OF NARROW-BANDWIDTH SINGLE PHOTONS USING ELECTROMAGNETICALLY INDUCED TRANSPARENCY IN ATOMIC ENSEMBLES

We review recent experiments [M. D. Eisaman et al., Nature438 (2005) 837] demonstrating the generation of narrow-bandwidth single photons using a room-temperature ensemble of 87Rb atoms. Our method involves creation of an atomic coherence via Raman scattering and projective measurement, followed by the coherent transfer of this atomic coherence onto a single photon using electromagnetically induced transparency (EIT). The single photons generated using this method are shown to have many properties necessary for quantum information protocols, such as narrow bandwidths, directional emission, and controllable pulse shapes. The narrow bandwidths of these single photons (~MHz), resulting from their matching to the EIT resonance (~MHz), allow them to be stored in narrow-bandwidth quantum memories. We demonstrate this by using dynamic EIT to store and retrieve the single photons in a second ensemble for storage times up to a few microseconds. We also describe recent improvements to the single-photon fidelity compared to the work by M. D. Eisaman in Nature438 (2005) 837. These techniques may prove useful in quantum information applications such as quantum repeaters, linear-optics quantum computation, and daytime free-space quantum communication.

Toward Quantum Control of Single Photons

Researchers are exploring ways to use electromagnetically induced transparency on individual light quanta, laying the groundwork for intriguing applications in quantum information science that use photons as information carriers, and atomic ensembles as memory and processing nodes.

Experimental test of non-local realism using a fiber-based source of polarization-entangled photon pairs

We test local realistic and non-local realistic theories using a fiber-based source of polarization-entangled photons. Our measurements violate local (certain non-local) hidden-variable theories by 15 (Leggett, A.) standard deviations.

Multi-photon entanglement: from quantum curiosity to quantum computing and quantum repeaters

In the emerging field of quantum information technology the two basic subfields are quantum communication and quantum computation. Photonic qubits are considered as most promising information carriers for this new technology due to the immense advantage of suffering negligible decoherence. Additionally, the very small photon-photon interactions can be replaced by inducing effective nonlinearities via measurements which allow for the implementation of crucial two-qubit gate operations. Although the spontaneous parametric down-conversion gives access to the generation of highly entangled few-photon states, such as four-qubit cluster states which allow to demonstrate the new concept of the one-way quantum computer, its applicability is highly limited due to the poor scaling of the simultaneous emission of more than one-entangled photon pair. Therefore of particular interest is the reversible mapping of qubits from photon states to atomic states. This might allow the implementation of photonic quantum repeaters for long-distance quantum communication or the generation of arbitrary multi-photon states as required for linear-optics quantum computing. Thus for the realization of such a quantum network several approaches for achieving the required quantum control between matter and photons have been studied during the past few years. Recent experiments demonstrating the generation of narrow-bandwidth single photons using a room-temperature ensemble of 87Rb atoms and electromagnetically induced transparency should emphasize the progress towards such a quantum network.

Quantum Control of Light using Coherent Atomic Memory

We describe our recent work using atomic ensembles to store quantum states of light and control light propagation and its quantum properties.

Microstructure-fiber-based source of high-flux hyperentangled photon-pairs

We generate hyperentangled (time-bin and polarization) photon-pairs using a microstructure-fiber Sagnac interferometer. Two-photon interference visibilities in both degrees of freedom are > 84%, and Bellpsilas inequality is violated by 27 sigma at 1-kHz coincidence rate.

Quantum Noise of Single-Photon Sources Based on Electromagnetically Induced Transparency

We analyze the quantum properties of single-photon sources based on atomic ensembles under realistic experimental conditions. This explains the experimentally observed enhanced photon correlations in the wings of a spectrally resolved g2measurement.