Publications


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.


Single-photon-level quantum memory at room temperature

Physical Review Letters 107 (2011)

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. © 2011 American Physical Society.


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


High-performance single-photon generation with commercial-grade optical fiber

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

C Söller, O Cohen, BJ Smith, IA Walmsley, C Silberhorn

High-quality quantum sources are of paramount importance for the implementation of quantum technologies. We present here a heralded single-photon source based on commercial-grade polarization-maintaining optical fiber. The heralded photons exhibit a purity of at least 0.84 and an unprecedented heralding efficiency into a single-mode fiber of 85%. The birefringent phase-matching condition of the underlying four-wave mixing process can be controlled mechanically to optimize the wavelength tuning needed for interfacing multiple sources, as is required for large-scale entanglement generation. © 2011 American Physical Society.


Real-World Quantum Sensors: Evaluating Resources for Precision Measurement

Physical Review Letters 107 (2011) 113603-113603

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


Quantum random bit generation using stimulated Raman scattering

Optics Express 19 (2011) 25173-25180

PJ Bustard, D Moffatt, R Lausten, G Wu, IA Walmsley, BJ Sussman

Random number sequences are a critical resource in a wide variety of information systems, including applications in cryptography, simulation, and data sampling. We introduce a quantum random number generator based on the phase measurement of Stokes light generated by amplification of zero-point vacuum fluctuations using stimulated Raman scattering. This is an example of quantum noise amplification using the most noise-free process possible: near unitary quantum evolution. The use of phase offers robustness to classical pump noise and the ability to generate multiple bits per measurement. The Stokes light is generated with high intensity and as a result, fast detectors with high signal-to-noise ratios can be used for measurement, eliminating the need for single-photon sensitive devices. The demonstrated implementation uses optical phonons in bulk diamond. © 2011 Optical Society of America.


Quantum Correlations using Strong Optical Pulses in Rare Earth Ion Doped Crystals

2011 CONFERENCE ON LASERS AND ELECTRO-OPTICS (CLEO) (2011)

PM Ledingham, JJ Longdell, IEEE


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.


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.


Vectorial phase retrieval for linear characterization of attosecond pulses

Physical Review Letters 107 (2011)

O Raz, O Schwartz, D Austin, AS Wyatt, A Schiavi, O Smirnova, B Nadler, IA Walmsley, D Oron, N Dudovich

The waveforms of attosecond pulses produced by high-harmonic generation carry information on the electronic structure and dynamics in atomic and molecular systems. Current methods for the temporal characterization of such pulses have limited sensitivity and impose significant experimental complexity. We propose a new linear and all-optical method inspired by widely used multidimensional phase retrieval algorithms. Our new scheme is based on the spectral measurement of two attosecond sources and their interference. As an example, we focus on the case of spectral polarization measurements of attosecond pulses, relying on their most fundamental property-being well confined in time. We demonstrate this method numerically by reconstructing the temporal profiles of attosecond pulses generated from aligned CO2 molecules. © 2011 American Physical Society.


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.


Accuracy measurements and improvement for complete characterization of optical pulses from nonlinear processes via multiple spectral-shearing interferometry

Opt. Express OSA 19 (2011) 25

AS Wyatt, A Grün, PK Bates, O Chalus, J Biegert, IA Walmsley

We demonstrate that multiple spectral-shearing interferometry increases the precision and accuracy of measurements of the spectral phase of a complex pulse (time-bandwidth product $=$ 125) arising from self-phase modulation in a gas filled capillary. We verify that the measured interferometric phase is accurate to 0.1 rad across the full bandwidth by checking the consistency between the spectral phases of each individual shear measurement. The accuracy of extracting pulse parameters (group delay dispersion, pulse duration and peak intensity) for single shear measurements were verified to better than 10% by comparison with the multishear reconstruction. High order space-time coupling is quantified across a single transverse dimension, verifying the suitability of such pulses for use in strong field experiments.


Optimal experiment design for minimal tomography

Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)

J Nunn, BJ Smith, G Puentes, JS Lundeen, IA Walmsley

Given an experimental set-up and a fixed number of measurements, how should one take data in order to optimally reconstruct the state of a quantum system? We show how to calculate the optimal design explicitly. © 2010 Optical Society of America.


Complete characterization of weak-homodyne photon-number-resolving detectors: Applications to non-classical photonic state reconstructions

Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)

HB Coldenstrodt-Ronge, G Puentes, O Cohen, F Noriega, X Yang, JS Lundeen, BJ Smith, IA Walmsley

A novel detector combining phase sensitivity and photon-number resolution is experimentally characterized by measuring its positive-operator-value measurement set. Direct application to tomographic reconstruction of heralded single-photon states is presented. ©2010 Optical Society of America.


Phase-controlled photonic quantum circuits in laser written integrated optics

Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)

N Thomas-Peter, BJ Smith, D Kundys, PGR Smith, IA Walmsley

We present a direct UV-written integrated photonic circuit with on-chip phase control through a thermo-optic phase shifter. An arbitrary beam splitter and a two-photon NOON state are demonstrated with high visibility interference. © 2010 Optical Society of America.


Coherent optical memory with GHz bandwidth

Lasers and Electro-Optics/Quantum Electronics and Laser Science Conference: 2010 Laser Science to Photonic Applications, CLEO/QELS 2010 (2010)

KF Reim, J Nunn, VO Lorenz, BJ Sussman, KC Lee, NK Langford, D Jaksch, IA Walmsley

We demonstrate the coherent storage and retrieval of sub-nanosecond low-intensity light pulses with spectral bandwidths exceeding 1 GHz in cesium vapor, using the novel, far offresonant two-photon Raman memory protocol. © 2010 Optical Society of America.


Quantum memory in an optical lattice

Physical Review A - Atomic, Molecular, and Optical Physics 82 (2010)

J Nunn, U Dorner, P Michelberger, KF Reim, KC Lee, NK Langford, IA Walmsley, D Jaksch

Arrays of atoms trapped in optical lattices are appealing as storage media for photons, since motional dephasing of the atoms is eliminated. The regular lattice is also associated with band structure in the dispersion experienced by incident photons. Here we study the influence of this band structure on the efficiency of quantum memories based on electromagnetically induced transparency (EIT) and on Raman absorption. We observe a number of interesting effects, such as both reduced and superluminal group velocities, enhanced atom-photon coupling, and anomalous transmission. These effects are ultimately deleterious to the memory efficiency, but they are easily avoided by tuning the optical fields away from the band edges. © 2010 The American Physical Society.


COMPONENTS FOR MULTI-PHOTON NON-CLASSICAL STATE PREPARATION AND MEASUREMENT

LASER SPECTROSCOPY (2010) 148-157

G Puentes, L Zhang, H Coldenstrodt-Ronge, O Cohen, BJ Smith, N Thomas-Peter, IA Walmsley


Resolution of the relative phase ambiguity in spectral shearing interferometry of ultrashort pulses.

Opt Lett 35 (2010) 1971-1973

DR Austin, T Witting, IA Walmsley

We show that multiple-shear spectral shearing interferometry can overcome the relative phase ambiguity of disjoint spectral components that is present in single-shear approaches. By upconverting the unknown pulse with spatially chirped ancillae, we achieve a shear-to-space mapping that can be acquired on an imaging spectrometer. A subset of this continuous range of shears can be chosen for robust and accurate phase retrieval using a multiple-shear algorithm.

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