Quantum Optics

Bright single photon emission from a quantum dot in a circular Bragg grating microcavity

by Serkan Ates

Submitted for publication

Bright single photon emission from single quantum dots in suspended circular Bragg grating microcavities is... more Bright single photon emission from single quantum dots in suspended circular Bragg grating microcavities is demonstrated. This geometry has been designed to achieve efficient (> 50 %) single photon extraction into a near-Gaussian shaped far-field pattern, modest (~10x) Purcell enhancement of the radiative rate, and a spectral bandwidth of a few nanometers. Measurements of fabricated devices show progress towards these goals, with collection efficiencies as high as ~10% demonstrated with moderate spectral bandwidth and rate enhancement. Photon correlation measurements are performed under above-bandgap excitation (pump wavelength = 780 nm to 820 nm) and confirm the single photon character of the collected emission. While the measured sources are all antibunched and dominantly composed of single photons, the multi-photon probability varies significantly. Devices exhibiting tradeoffs between collection efficiency, Purcell enhancement, and multi-photon probability are explored and the results are interpreted with the help of finite-difference time-domain simulations. Below-bandgap excitation resonant with higher states of the quantum dot and/or cavity (pump wavelength = 860 nm to 900 nm) shows a near-complete suppression of multi-photon events and may circumvent some of the aforementioned tradeoffs.

Background-free quantum frequency conversion of single photons from a semiconductor quantum dot

by Serkan Ates

Submitter for publication

We demonstrate background-free quantum frequency conversion of single photons from an epitaxially-grown InAs quantum... more We demonstrate background-free quantum frequency conversion of single photons from an epitaxially-grown InAs quantum dot. Single photons at ~ 980 nm are combined with a pump laser near 1550 nm inside a periodically-poled lithium niobate (PPLN) waveguide, generating single photons at ~ 600 nm. The large red-detuning between the pump and signal wavelengths ensures nearly background-free conversion, avoiding processes such as upconversion of anti-Stokes Raman scattered pump photons in the PPLN crystal. Second-order correlation measurements on the single photon stream are performed both before and after conversion, confirming the preservation of photon statistics during the frequency conversion process.

Immunity of information encoded in decoherence-free subspaces to particle loss

by Piotr Migdal

Quantum and semiclassical polarization correlations

by Piotr Migdal

Noise reduction in 3D noncollinear parametric amplifier

by Piotr Migdal

Spintronics and quantum optics in InAs/GaAs quantum dots

by Claudio Polisseni

Third year project report for my BSc degree. Credit to Prof. Murray and Dr. Spencer for the help and the support they gave me.

Coherent State Distinguishability in Continuous Variable Quantum Cryptography

by Mile Gu

Operational Significance of Discord: Theory and Experiment

by Mile Gu

Observations that coherent interactions between non-entangled systems can still exhibit unique quantum behaviour... more Observations that coherent interactions between non-entangled systems can still exhibit unique quantum behaviour challenged the traditional view that quantum correlations are synonymous with entanglement. In response, quantum discord was proposed to complete the description of all quantum correlations. Nevertheless, explicit protocols that directly exploit discord as a quantum resource have remained elusive. Here, we demonstrate that under certain measurement constraints, discord between bipartite systems directly quantifies a quantum resource that coherent interactions can harness. The inability to access this resource by any other means allows us to use discord to directly quantify this `quantum advantage'. We experimentally encode information within the discordant correlations of two separable Gaussian states. The amount of extra information recovered by coherent interaction is quantified and directly linked with the discord between the states. No entanglement exists at any point of this experiment. Thus we introduce and demonstrate an operational meaning for quantum discord.

Building Gaussian cluster states by linear optics

by Mile Gu

Nonclassical Properties of Nondegenerate Parametric Amplifiers and Oscillators with Pump Depletion and Nonhomogeneous Losses, using the Wigner Representation.

by Jesus Martinez Linares

Jesús Martínez-Linares and P. García-Fernández, Journal of Modern Optics 41, 67-88 (1994). Índice de impacto 1.717. Revista 14 de 54 en el área de Óptica (2004). ISSN: 0950-0340. Editorial Taylor & Francis.

The squeezing properties of non-degenerate parametric amplification and oscillation with pump depletion and... more The squeezing properties of non-degenerate parametric amplification and oscillation with pump depletion and non-homogeneous absorption losses are studied. A method based on the Wigner representation is used which allows one, within a linearization scheme, to derive directly the Langevin equations for the involved optical fields from their quantum Heisenberg equations. Non-homogeneous absorption losses for the three beams are included in order to analyze the sensitivity of the squeezing spectra to the asymmetry of the losses. Intracavity squeezing spectra are calculated within this method both below- and above-threshold regimes. Special attention is given to the squeezing properties of the phase sum and amplitude difference of the correlated beams and amplitude of a single beam above threshold, where the role of loss asymmetry and pump losses are analyized in detail.

Duality with Macroscopic Which-Way Detectors

by Jesus Martinez Linares

Jesús Martínez Linares and David Harmin. Proceedings of the Fifth International Conference on Squeezed States and Uncertainty Relations, NASA-Goddard Conference Publication Series (1998), pp. 379-384, NASA/CP-1998-206855.

Quantum optical test of complementarity are usually illustrated with the help of a quantum optical Ramsey... more Quantum optical test of complementarity are usually illustrated with the help of a quantum optical Ramsey interferometer, in which a quantized microwave field in a resonator acts jointly as a beam splitter and a which-way detector. We show here that resonant interaction of an atom with an intense coherente field (macroscopic detector) can result in a nearly complete loss of the atomic fringe visibility measured at the output port of the interferometer. This result shows that just resorting to the macrocopic intensity domain is not a sufficient condition for the recovering the classical limit of coherent beam splitters.

Schmidt modes generated in parametric downconversion

by Filippo Miatto

This paper presents the general Schmidt decomposition of two-photon fields generated in spontaneous parametric... more This paper presents the general Schmidt decomposition of two-photon fields generated in spontaneous parametric down-conversion (SPDC). It discusses in particular the separation of the radial and azimuthal degrees of freedom, the role of projection in modal analysis, and the benefits of collinear phase mismatch. The paper is written in a review style and presents a wealth of numerical results. It aims at emphasising the physics beyond the mathematics, through discussions and graphical representations of key results.

A general approach to quantum dynamics using a variational master equation: Application to phonon-damped Rabi rotations in quantum dots

by Nike Dattani

2011 - Published in Physical Review B Rapid Communications

Photoabsorption of attosecond XUV light pulses by two strongly laser-coupled autoionizing states

by Wei-Chun Chu

We study theoretically the photoabsorption spectra of an attosecond extreme ultraviolet (XUV) pulse by a laser-dressed... more We study theoretically the photoabsorption spectra of an attosecond extreme ultraviolet (XUV) pulse by a laser-dressed atomic system. A weak XUV excites an autoionizing state which is strongly coupled to another autoionizing state by a laser. The theory was applied to explain two recent experiments [ Loh, Greene and Leone Chem. Phys. 350 7 (2008); Wang, Chini, Chen, Zhang, Cheng, He, Cheng, Wu, Thumm and Chang Phys. Rev. Lett. 105 143002 (2010)] where the absorption spectra of the XUV lights were measured against the time delay between the laser and the XUV. In another example, we study an attosecond pulse exciting the 2s2p(1 P) resonance of helium which is resonantly coupled to the 2s2(1 S) resonance by a moderately intense 540-nm laser. The relation between the photoabsorption spectra and the photoelectron spectra and the modification of the transmitted lights in such an experiment are analyzed. The role of Rabi flopping between the two autoionizing states within their lifetimes is investigated with respect to the laser intensity and detuning.

Bounds and optimisation of orbital angular momentum bandwidths within parametric down-conversion systems

by Filippo Miatto

The measurement of high-dimensional entangled states of orbital angular momentum prepared by spontaneous parametric... more The measurement of high-dimensional entangled states of orbital angular momentum prepared by spontaneous parametric down-conversion can be considered in two separate stages: a generation stage and a detection stage. Given a certain number of generated modes, the number of measured modes is determined by the measurement apparatus. We derive a simple relationship between the generation and detection parameters and the number of measured entangled modes.

A Theoretical Analysis of Quantum Imaging through Turbulence

by David Simon

K.W.C. Chan, D.S. Simon, A.V. Sergienko, N.C. Hardy, J.H. Shapiro, P. Ben Dixon, Gregory Howland, John C. Howell, Joseph H. Eberly, M.N. O'Sullivan, B. Rodenburg, Robert W. Boyd, Phys. Rev. A 84, 043807 (2011).

Evaluation of Polarization Mode Dispersion and Chromatic Dispersion using Quantum Interferometry

by David Simon

A. Fraine, D.S. Simon, O. Minaeva, R. Egorov, and A.V. Sergienko, Optics Express 19, 22820-22836 (2011)

Quantum ghost imaging through turbulence

by David Simon

P.B. Dixon, G. Howland, K.W.C. Chan, C. O'Sullivan-Hale, B. Rodenburg, N.C. Hardy,  D.S. Simon, J.H. Shapiro, A.V. Sergienko, R.W. Boyd, J.C. Howell, Physical Review A 83, 051803(R) (2011)

Spatial-Dispersion Cancellation in Quantum Interferometry

by David Simon

D.S. Simon and A.V. Sergienko, Phys. Rev. A, 80, 053813  (2009)

Multiparameter Entangled State Engineering Using Adaptive Optics

by David Simon

C. Bonato, D.S. Simon, P. Villoresi, A.V. Sergienko, Phys. Rev. A, 79, 062304 (2009). (Chosen for reprinting in Virtual Journal of Quantum Information, 9, no. 6 2009)