Heralded generation of single photons in pure quantum states

Journal of Modern Optics 59 (2012) 1525-1537

L Zhang, C Söller, O Cohen, BJ Smith, IA Walmsley

Sources of single photons in pure quantum states are essential to many quantum optics applications. We explore a technique, known as group-velocity matching, that enables the heralded generation of pure single photons through nonlinear optical processes. It reduces or eliminates the requirement of spectral filtering that conventional sources rely on to achieve high purity, therefore increasing both heralding efficiency and photon flux. Implementation in both spontaneous parametric downconversion and spontaneous four-wave mixing is studied as we discuss several recent experimental realizations demonstrating purity of more than 0.84 for the heralded photons. © 2012 Copyright Taylor and Francis Group, LLC.

Turning classical states quantum with linear optics and photon counting

2012 Conference on Lasers and Electro-Optics, CLEO 2012 (2012)

TJ Bartley, G Donati, XM Jin, JB Spring, M Barbieri, BJ Smith, A Datta, L Zhang, IA Walmsley

We demonstrate a method to transmute classical light into a quantum state without invoking any nonlinear optical processes. Using a tunable beam splitter and photon number resolving measurement, we create a novel non-Gaussian state. © 2012 OSA.

Synchronizing single photons with quantum memories

2012 Conference on Lasers and Electro-Optics, CLEO 2012 (2012)

J Nunn, NK Langford, T Champion, MR Sprague, PS Michelberger, KC Lee, XM Jin, D England, WS Kolthammer, IA Walmsley

Without deterministic single photon sources, multiphoton rates fall exponentially with the number of photons required, making practical photonics unfeasible. We show how quantum memories improve multiphoton rates by many orders of magnitude. © 2012 OSA.

From molecular control to quantum technology with the dynamic Stark effect

Faraday Discussions 153 (2011) 321-342

PJ Bustard, G Wu, R Lausten, D Townsend, IA Walmsley, A Stolow, BJ Sussman

The non-resonant dynamic Stark effect is a powerful and general way of manipulating ultrafast processes in atoms, molecules, and solids with exquisite precision. We discuss the physics behind this effect, and demonstrate its efficacy as a method of control in a variety of systems. These applications range from the control of molecular rotational dynamics to the manipulation of chemical reaction dynamics, and from the suppression of vacuum fluctuation effects in coherent preparation of matter, to the dynamic generation of bandwidth for storage of broadband quantum states of light. © 2011 The Royal Society of Chemistry.

Lateral shearing interferometry of high-harmonic wavefronts

Opt. Lett. OSA 36 (2011) 10

DR Austin, T Witting, CA Arrell, F Frank, AS Wyatt, JP Marangos, JWG Tisch, IA Walmsley

We present a technique for frequency-resolved wavefront characterization of high harmonics based on lateral shearing interferometry. Tilted replicas of the driving laser pulse are produced by a Mach–Zehnder interferometer, producing separate focii in the target. The interference of the resulting harmonics on a flat-field extreme ultraviolet spectrometer yields the spatial phase derivative. A comprehensive set of spatial profiles, resolved by harmonic order, validate the technique and reveal the interplay of single-atom and macroscopic effects.

Femtosecond to attosecond light pulses from a molecular modulator

NATURE PHOTONICS 5 (2011) 665-672

S Baker, IA Walmsley, JWG Tisch, JP Marangos

Engineering Nonlinear Optic Sources of Photonic Entanglement

PROGRESS IN OPTICS, VOL 56 56 (2011) 227-331

JP Torres, K Banaszek, IA Walmsley

Quantum correlations using strong optical pulses in rare earth ion doped crystals

Optics InfoBase Conference Papers (2011)

PM Ledingham, JJ Longdell

We use photon echo based protocols with cryogenic rare earth ion dopants to create photon streams with time separated correlations. Theoretically, these streams are non-classically correlated. We present progress toward realizing this correlation. © 2010 Optical Society of America.

Photon-echo quantum memories in inhomogeneously broadened two-level atoms

PHYSICAL REVIEW A 84 (2011) ARTN 022309

DL McAuslan, PM Ledingham, WR Naylor, SE Beavan, MP Hedges, MJ Sellars, JJ Longdell

Quantum correlations using strong optical pulses in rare earth ion doped crystals

2011 Conference on Lasers and Electro-Optics: Laser Science to Photonic Applications, CLEO 2011 (2011)

PM Ledingham, JJ Longdell

We use photon echo based protocols with cryogenic rare earth ion dopants to create photon streams with time separated correlations. Theoretically, these streams are non-classically correlated. We present progress toward realizing this correlation. © 2011 OSA.

Photon echo without a free induction decay in a double-Λ system.

Optics letters 36 (2011) 1272-1274

SE Beavan, PM Ledingham, JJ Longdell, MJ Sellars

We have characterized a novel photon-echo pulse sequence for a double-Λ-type energy level system where the input and rephasing transitions are different from the applied π pulses. We show that, despite having imperfect π-pulses associated with large coherent emission due to free induction decay (FID), the noise added in the echo mode is only 0.2 ± 0.1 photons per shot, compared to 4 × 10⁴ photons in the FID modes. Using this echo pulse sequence in the "rephased amplified spontaneous emission" (RASE) scheme [Phys. Rev. A 81, 012301 (2010)] will allow for generation of entangled photon pairs that are in different frequency, temporal, and potentially spatial modes to any bright driving fields. The coherence and efficiency properties of this sequence were characterized in a Pr(3+):Y₂SiO₅ crystal.

Coherent detection of ultrasound using spectral hole burning media


JW Tay, PM Ledingham, JJ Longdell

Quantum metrology with imperfect states and detectors

Physical Review A 83 (2011) 6

A Datta, L Zhang, N Thomas-Peter, U Dorner, B Smith, IA Walmsley

Extending electron orbital precession to the molecular case: Use of orbital alignment for observation of wavepacket dynamics

Physical Review A - Atomic, Molecular, and Optical Physics 83 (2011)

HEL Martay, DG England, DJ McCabe, IA Walmsley

The complexity of ultrafast molecular photoionization presents an obstacle to the modeling of pump-probe experiments. Here, a simple optimized model of atomic rubidium is combined with a molecular dynamics model to predict quantitatively the results of a pump-probe experiment in which long-range rubidium dimers are first excited, then ionized after a variable delay. The method is illustrated by the outline of two proposed feasible experiments and the calculation of their outcomes. Both of these proposals use Feshbach Rb872 molecules. We show that long-range molecular pump-probe experiments should observe spin-orbit precession given a suitable pump pulse, and that the associated high-frequency beat signal in the ionization probability decays after a few tens of picoseconds. If the molecule was to be excited to only a single fine-structure state, then a low-frequency oscillation in the internuclear separation would be detectable through the time-dependent ionization cross section, giving a mechanism that would enable observation of coherent vibrational motion in this molecule. © 2011 American Physical Society.

High-speed electrical control of a solid-state photonic quantum interface


AB de la Giroday, AJ Bennett, MA Pooley, RM Stevenson, N Skoeld, RB Patel, I Farrer, DA Ritchie, AJ Shields, IEEE

Semiconductor Single Photon Devices for Quantum Information Processing


O Thomas, CL Salter, AJ Bennett, RM Stevenson, MA Pooley, MB Ward, RB Patel, AB de la Giroday, N Skold, I Farrer, CA Nicoll, DA Ritchie, AJ Shields

Coherent coupling of the excitonic states in a single quantum dot


AJ Bennett, MA Pooley, RM Stevenson, MB Ward, RB Patel, AB de la Giroday, N Skoeld, I Farrer, CA Nicoll, DA Ritchie, AJ Shields

Two-photon interference using electrically tunable remote quantum dots


RB Patel, AJ Bennett, I Farrer, CA Nicoll, DA Ritchie, AJ Shields

Single-photon-level quantum memory at room temperature.

Phys Rev Lett 107 (2011) 053603-

KF Reim, P Michelberger, KC Lee, J Nunn, NK Langford, IA Walmsley

Room-temperature, easy-to-operate quantum memories are essential building blocks for future long distance quantum information networks operating on an intercontinental scale, because devices like quantum repeaters, based on quantum memories, will have to be deployed in potentially remote, inaccessible locations. Here we demonstrate controllable, broadband and efficient storage and retrieval of weak coherent light pulses at the single-photon level in warm atomic cesium vapor using the robust far off-resonant Raman memory scheme. We show that the unconditional noise floor of this technically simple quantum memory is low enough to operate in the quantum regime, even in a room-temperature environment.

Integrated photonic sensing

New Journal of Physics 13 (2011)

N Thomas-Peter, NK Langford, A Datta, L Zhang, BJ Smith, JB Spring, BJ Metcalf, HB Coldenstrodt-Ronge, M Hu, J Nunn, IA Walmsley

Loss is a critical roadblock to achieving photonic quantum-enhanced technologies. We explore a modular platform for implementing integrated photonics experiments and consider the effects of loss at different stages of these experiments, including state preparation, manipulation and measurement. We frame our discussion mainly in the context of quantum sensing and focus particularly on the use of loss-tolerant Holland-Burnett states for optical phase estimation. In particular, we discuss spontaneous four-wave mixing in standard birefringent fibre as a source of pure, heralded single photons and present methods of optimizing such sources. We also outline a route to programmable circuits that allows the control of photonic interactions even in the presence of fabrication imperfections and describe a ratiometric characterization method for beam splitters, which allows the characterization of complex circuits without the need for full process tomography. Finally, we present a framework for performing state tomography on heralded states using lossy measurement devices. This is motivated by a calculation of the effects of fabrication imperfections on precision measurement using Holland-Burnett states. © IOP Publishing Ltd and Deutsche Physikalische Gesellschaft.