Jean-Philippe W. MacLean

Storage and retrieval of THz-bandwidth single photons using a room-temperature diamond quantum memory.

We report the storage and retrieval of single photons, via a quantum memory, in the optical phonons of a room-temperature bulk diamond. The THz-bandwidth heralded photons are generated by spontaneous parametric down-conversion and mapped to phonons via a Raman transition, stored for a variable delay, and released on demand. The second-order correlation of the memory output is g((2))(0)=0.65±0.07, demonstrating a preservation of nonclassical photon statistics throughout storage and retrieval. The memory is low noise, high speed and broadly tunable; it therefore promises to be a versatile light-matter interface for local quantum processing applications.

Frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory.

The spectral manipulation of photons is essential for linking components in a quantum network. Large frequency shifts are needed for conversion between optical and telecommunication frequencies, while smaller shifts are useful for frequency-multiplexing quantum systems, in the same way that wavelength division multiplexing is used in classical communications. Here we demonstrate frequency and bandwidth conversion of single photons in a room-temperature diamond quantum memory. Heralded 723.5 nm photons, with 4.1 nm bandwidth, are stored as optical phonons in the diamond via a Raman transition. Upon retrieval from the diamond memory, the spectral shape of the photons is determined by a tunable read pulse through the reverse Raman transition. We report central frequency tunability over 4.2 times the input bandwidth, and bandwidth modulation between 0.5 and 1.9 times the input bandwidth. Our results demonstrate the potential for diamond, and Raman memories in general, as an integrated platform for photon storage and spectral conversion.Kent A.G. Fisher,1 Duncan G. England,2 Jean-Philippe W. MacLean,1 Philip J. Bustard,2 Kevin J. Resch,1 and Benjamin J. Sussman2, 3 Institute for Quantum Computing and Department of Physics & Astronomy, University of Waterloo, 200 University Avenue West, Waterloo, Ontario N2L 3G1, Canada National Research Council of Canada, 100 Sussex Drive, Ottawa, Ontario, K1A 0R6, Canada Physics Department, University of Ottawa, 150 Louis Pasteur, Ottawa, Ontario, K1N 6N5, Canada (Dated: September 21, 2015)

Quantum-coherent mixtures of causal relations.

Understanding the causal influences that hold among parts of a system is critical both to explaining that systems natural behaviour and to controlling it through targeted interventions. In a quantum world, understanding causal relations is equally important, but the set of possibilities is far richer. The two basic ways in which a pair of time-ordered quantum systems may be causally related are by a cause-effect mechanism or by a common-cause acting on both. Here we show a coherent mixture of these two possibilities. We realize this nonclassical causal relation in a quantum optics experiment and derive a set of criteria for witnessing the coherence based on a quantum version of Berksons effect, whereby two independent causes can become correlated on observation of their common effect. The interplay of causality and quantum theory lies at the heart of challenging foundational puzzles, including Bells theorem and the search for quantum gravity.

Storage of polarization-entangled THz-bandwidth photons in a diamond quantum memory

Bulk diamond phonons have been shown to be a versatile platform for the generation, storage, and manipulation of high-bandwidth quantum states of light. Here we demonstrate a diamond quantum memory that stores, and releases on demand, an arbitrarily polarized

Phonon-Mediated Nonclassical Interference in Diamond.

\sim

A quantum light-matter beamsplitter in diamond

250 fs duration photonic qubit. The single-mode nature of the memory is overcome by mapping the two degrees of polarization of the qubit, via Raman transitions, onto two spatially distinct optical phonon modes located in the same diamond crystal. The two modes are coherently recombined upon retrieval and quantum process tomography confirms that the memory faithfully reproduces the input state with average fidelity

Quantum to classical transitions in causal relations

0.784\pm0.004

Applications of a picosecond-lifetime quantum memory

with a total memory efficiency of

Storage and retrieval of ultrafast single photons using a room-temperature diamond quantum memory

(0.76\pm0.03)\%

Direct Characterization of Ultrafast Energy-Time Entangled Photon Pairs

. In an additional demonstration, one photon of a polarization-entangled pair is stored in the memory. We report that entanglement persists in the retrieved state for up to 1.3 ps of storage time. These results demonstrate that the diamond phonon platform can be used in concert with polarization qubits, a key requirement for polarization-encoded photonic processing.