Characterization of the femtosecond speckle field of a multiply scattering medium via spatio-spectral interferometry


A Tajalli, DJ McCabe, DR Austin, IA Walmsley, B Chatel

Mapping coherence in measurement via full quantum tomography of a hybrid optical detector

Nature Photonics 6 (2012) 364-368

L Zhang, HB Coldenstrodt-Ronge, A Datta, G Puentes, JS Lundeen, XM Jin, BJ Smith, MB Plenio, IA Walmsley

Quantum states and measurements exhibit wave-like (continuous) or particle-like (discrete) character. Hybrid discrete-continuous photonic systems are key to investigating fundamental quantum phenomena1-3, generating superpositions of macroscopic states4, and form essential resources for quantum-enhanced applications5 such as entanglement distillation6,7 and quantum computation8, as well as highly efficient optical telecommunications9,10. Realizing the full potential of these hybrid systems requires quantum-optical measurements sensitive to non-commuting observables such as field quadrature amplitude and photon number11-13. However, a thorough understanding of the practical performance of an optical detector interpolating between these two regions is absent. Here, we report the implementation of full quantum detector tomography, enabling the characterization of the simultaneous wave and photon-number sensitivities of quantum-optical detectors. This yields the largest parameterization to date in quantum tomography experiments, requiring the development of novel theoretical tools. Our results reveal the role of coherence in quantum measurements and demonstrate the tunability of hybrid quantum-optical detectors. © 2012 Macmillan Publishers Limited. All rights reserved.

Continuous phase stabilization and active interferometer control using two modes


G Jotzu, TJ Bartley, HB Coldenstrodt-Ronge, BJ Smith, IA Walmsley

Entangbling - quantum correlations in diamond


IA Walmsley, IEEE

Quantum metrology without quantum entanglement

Modern Physics Letters B 26 (2012)

A Datta, A Shaji

We scrutinize the role of quantum entanglement in quantum metrology and discuss recent advances in nonlinear quantum metrology that allow improved scalings of the measurement precision with respect to the available resources. Such schemes can surpass the conventional Heisenberg limited scaling of 1/N of quantum enhanced metrology. Without investing in the preparation of entangled states, we review how systems with intrinsic nonlinearities such as BoseEinstein condensates and light-matter interfaces can provide improved scaling in single parameter estimation. © 2012 World Scientific Publishing Company.

Adaptive slit beam shaping for direct laser written waveguides.

Opt Lett 37 (2012) 470-472

PS Salter, A Jesacher, JB Spring, BJ Metcalf, N Thomas-Peter, RD Simmonds, NK Langford, IA Walmsley, MJ Booth

We demonstrate an improved method for fabricating optical waveguides in bulk materials by means of femtosecond laser writing. We use an LC spatial light modulator (SLM) to shape the beam focus by generating adaptive slit illumination in the pupil of the objective lens. A diffraction grating is applied in a strip across the SLM to simulate a slit, with the first diffracted order mapped onto the pupil plane of the objective lens while the zeroth order is blocked. This technique enables real-time control of the beam-shaping parameters during writing, facilitating the fabrication of more complicated structures than is possible using nonadaptive methods. Waveguides are demonstrated in fused silica with a coupling loss to single-mode fibers in the range of 0.2 to 0.5 dB and propagation loss <0.4 dB/cm.

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.

Generalized multishearing interferometry for the complete multidimensional characterization of optical beams and ultrashort pulses

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

AS Wyatt, J Biegert, IA Walmsley

We demonstrate increased accuracy and precision in the reconstruction of the multidimensional phase of electromagnetic fields based on multiple spectral shearing interferometry measurements made with shears of an arbitrary magnitude. © 2012 OSA.

Experimental realization of light with time-separated correlations by rephasing amplified spontaneous emission.

Physical review letters 109 (2012) 093602-

PM Ledingham, WR Naylor, JJ Longdell

Amplified spontaneous emission is a common noise source in active optical systems, it is generally seen as being an incoherent process. Here we excite an ensemble of rare earth ion dopants in a solid with a π pulse, resulting in amplified spontaneous emission. The application of a second π pulse leads to a coherent echo of the amplified spontaneous emission that is correlated in both amplitude and phase. For small optical thicknesses, we see evidence that the amplified spontaneous emission and its echo are entangled.

Quantum storage of a photonic polarization qubit in a solid

Physical Review Letters 108 (2012)

M Gündoǧan, PM Ledingham, A Almasi, M Cristiani, H De Riedmatten

We report on the quantum storage and retrieval of photonic polarization quantum bits onto and out of a solid state storage device. The qubits are implemented with weak coherent states at the single photon level, and are stored for a predetermined time of 500 ns in a praseodymium doped crystal with a storage and retrieval efficiency of 10%, using the atomic frequency comb scheme. We characterize the storage by using quantum state tomography, and find that the average conditional fidelity of the retrieved qubits exceeds 95% for a mean photon number μ=0.4. This is significantly higher than a classical benchmark, taking into account the Poissonian statistics and finite memory efficiency, which proves that our crystal functions as a quantum storage device for polarization qubits. These results extend the storage capabilities of solid state quantum light matter interfaces to polarization encoding, which is widely used in quantum information science. © 2012 American Physical Society.

Quantum diamonds

Optics and Photonics News 23 (2012) 34-41

J Nunn, I Walmsley

Quantum optics: Discord in the ranks

Nature Photonics 6 (2012) 724-725

A Datta

Compact Continuous-Variable Entanglement Distillation


A Datta, L Zhang, J Nunn, NK Langford, A Feito, MB Plenio, IA Walmsley

Controlled-NOT gate operating with single photons


MA Pooley, DJP Ellis, RB Patel, AJ Bennett, KHA Chan, I Farrer, DA Ritchie, AJ Shields

Mapping coherence in measurement via full quantum tomography of a hybrid optical detector

Nature Photonics (2012)

L Zhang, HB Coldenstrodt-Ronge, A Datta, G Puentes, JS Lundeen, X-M Jin, BJ Smith, MB Plenio, IA Walmsley

Compact continuous-variable entanglement distillation

Physical Review Letters 108 (2012)

A Datta, L Zhang, J Nunn, NK Langford, A Feito, MB Plenio, IA Walmsley

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


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.

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.