arXiv subjects

Alex Hayat

Publications and source records attributed to Alex Hayat.

33 records · Page 2Linked to original sources

arXiv2013

Experimental demonstration of a time-domain multidimensional quantum channel

We present the first experimental realization of a flexible multidimensional quantum channel where the Hilbert space dimensionality can be controlled electronically. Using electro-optical modulators (EOM) and narrow-band optical filters, quantum information is encoded and decoded in the temporal degrees of freedom of photons from a long-coherence-time single-photon source. Our results demonstrate the feasibility of a generic scheme for encoding and transmitting multidimensional quantum information over the existing fiber-optical telecommunications infrastructure.

quant-ph↗

arXiv2013

A Note on Different Definitions of Momentum Disturbance

In [1], Busch et al. showed that it is possible to construct an error-disturbance relation having the same form as Heisenberg's original heuristic definition[2], in contrast to the theory proposed by Ozawa[3] which we and others recently confirmed experimentally[4,5]. With Ozawa's definitions of measurement error and disturbance, a relation of Heisenberg's form is not in general valid, and a new error-disturbance relationship can be derived. Here we explain the different physical significance of the two definitions, and suggest that Ozawa's definition better corresponds to the usual understanding of the disturbance that Heisenberg discussed.

quant-ph↗

arXiv2013

Observation of Transient Momentum-Space Interference During Scattering of a Condensate From an Optical Barrier

Scattering theory traditionally deals with the asymptotic behaviour of a system far removed from the actual scattering event. Here we present an experimental study of the one-dimensional scattering of a non-interacting condensate of 87-Rb atoms from a potential barrier in the non-asymptotic regime, for which the collision dynamics are still ongoing. We show that for near-transparent barriers, there are two distinct transient scattering effects that arise and dramatically change the momentum distribution during the collision: a deceleration of wavepacket components in mid-collision, and an interference between incident and transmitted portions of the wavepacket. Both effects lead to the re-distribution of momenta giving rise to a rich interference pattern that can be used to perform reconstruction of the single-particle phase profile.

cond-mat.quant-gas↗

arXiv2013

Observing the Onset of Effective Mass

The response of a particle in a periodic potential to an applied force is commonly described by an effective mass which accounts for the detailed interaction between the particle and the surrounding potential. Using a Bose-Einstein condensate of 87-Rb atoms initially in the ground band of an optical lattice, we experimentally show that the initial response of a particle to an applied force is in fact characterized by the bare mass. Subsequently, the particle response undergoes rapid oscillations and only over timescales long compared to that of the interband dynamics is the effective mass observed to be an appropriate description.

quant-ph↗

arXiv2013

Hybrid high-temperature superconductor-semiconductor tunnel diode

We report the demonstration of hybrid high-Tc-superconductor-semiconductor tunnel junctions, enabling new interdisciplinary directions in condensed matter research. The devices were fabricated by our newly-developed mechanical bonding technique, resulting in high-Tc-semiconductor planar junctions acting as superconducting tunnel diodes. Tunneling-spectra characterization of the hybrid junctions of Bi2Sr2CaCu2O8+δ combined with bulk GaAs, or a GaAs/AlGaAs quantum well, exhibits excess voltage and nonlinearity - in good agreement with theoretical predictions for a d-wave superconductor-normal material junction, and similar to spectra obtained in scanning tunneling microscopy. Additional junctions are demonstrated using Bi2Sr2CaCu2O8+δ combined with graphite or Bi2Te3. Our results pave the way for new methods in unconventional superconductivity studies, novel materials and quantum technology applications.

cond-mat.supr-con↗

arXiv2013

Multidimensional quantum information based on single-photon temporal wavepackets

We propose a multidimensional quantum information encoding approach based on temporal modulation of single photons, where the Hilbert space can be spanned by an in-principle infinite set of orthonormal temporal profiles. We analyze two specific realizations of such modulation schemes, and show that error rate per symbol can be smaller than 1% for practical implementations. Temporal modulation may enable multidimensional quantum communication over the existing fiber optical infrastructure, as well as provide an avenue for probing high-dimensional entanglement approaching the continuous limit.

quant-ph↗

arXiv2012

Proximity-induced high-temperature superconductivity in topological insulators Bi2Se3 and Bi2Te3

Interest in the superconducting proximity effect has been reinvigorated recently by novel optoelectronic applications as well as by the possible emergence of the elusive Majorana fermion at the interface between topological insulators and superconductors. Here we produce high-temperature superconductivity in Bi2Se3 and Bi2Te3 via proximity to Bi2Sr2CaCu2O8+δ, in order to access increasing temperature and energy scales for this phenomenon. This was achieved by a new mechanical bonding technique we developed, enabling the fabrication of high-quality junctions between materials, unobtainable by conventional approaches. We observe proximity-induced superconductivity in Bi2Se3 and Bi2Te3 persisting up to at least 80K, a temperature an order of magnitude higher than any previous observations. Moreover, the induced superconducting gap in our devices reaches values of 10mV, significantly enhancing the relevant energy scales. Our results open new directions for fundamental studies in condensed matter physics and enable a wide range of applications in spintronics and quantum computing.

cond-mat.supr-con↗

arXiv2012

Violation of Heisenberg's Measurement-Disturbance Relationship by Weak Measurements

While there is a rigorously proven relationship about uncertainties intrinsic to any quantum system, often referred to as "Heisenberg's Uncertainty Principle," Heisenberg originally formulated his ideas in terms of a relationship between the precision of a measurement and the disturbance it must create. Although this latter relationship is not rigorously proven, it is commonly believed (and taught) as an aspect of the broader uncertainty principle. Here, we experimentally observe a violation of Heisenberg's "measurement-disturbance relationship", using weak measurements to characterize a quantum system before and after it interacts with a measurement apparatus. Our experiment implements a 2010 proposal of Lund and Wiseman to confirm a revised measurement-disturbance relationship derived by Ozawa in 2003. Its results have broad implications for the foundations of quantum mechanics and for practical issues in quantum mechanics.

quant-ph↗

arXiv2012

Dynamic Stark Effect in Strongly Coupled Microcavity Exciton-Polaritons

We present experimental observations of a non-resonant dynamic Stark shift in strongly coupled microcavity quantum well exciton-polaritons - a system which provides a rich variety of solid-state collective phenomena. The Stark effect is demonstrated in a GaAs/AlGaAs system at 10K by femtosecond pump-probe measurements, with the blue shift approaching the meV scale for a pump fluence of 2 mJcm^-2 and 50 meV red detuning, in good agreement with theory. The energy level structure of the strongly coupled polariton Rabi-doublet remains unaffected by the blue shift. The demonstrated effect should allow generation of ultrafast density-independent potentials and imprinting well-defined phase profiles on polariton condensates, providing a powerful tool for manipulation of these condensates, similar to dipole potentials in cold atom systems.

cond-mat.quant-gas↗

arXiv2009

Non-local Ponderomotive Nonlinearity in Plasmonic

We analyze an inherent nonlinearity of Surface Plasmon Polaritons at the interface of Fermi-Dirac metal plasma, stemming from the depletion of electron density in high-field intensity regions. The derived optical nonlinear coefficients are comparable to the experimental values for metals. We calculate the dispersion relations for the nonlinear propagation of high-intensity Surface Plasmon Polaritons, predicting a nonlinear induced cutoff and vanishing group velocity.

physics.optics↗

arXiv2008

Infrared Single-Photon Detector based on Silicon Two-Photon Absorption

We propose a scheme for infrared single-photon detection based on two-photon absorption at room-temperature in Si avalanche photodiodes, where the detected photon's energy is lower than the bandgap and the energy difference is complemented by a pump field. A quantum non-perturbative model is developed for non-degenerate two-photon absorption in direct and indirect semiconductors yielding proper non-divergent rates allowing device efficiency optimization. The proposed monolithic detector is simple, miniature, integrable and does not require phase matching, while not compromising the performance and exhibiting even better efficiency than the competing up-conversion schemes (~1 order of magnitude) for similar optical pump levels.

cond-mat.mtrl-sci↗

arXiv2007

Two-Photon Emission from Semiconductors

We report the first experimental observations of two-photon emission from semiconductors, to the best of our knowledge, and develop a corresponding theory for the room-temperature process. Spontaneous two-photon emission is demonstrated in optically-pumped bulk GaAs and in electrically-driven GaInP/AlGaInP quantum wells. Singly-stimulated two-photon emission measurements demonstrate the theoretically predicted two-photon optical gain in semiconductors - a necessary ingredient for any realizations of future two-photon semiconductor lasers. Photon-coincidence experiment validates the simultaneity of the electrically-driven GaInP/AlGaInP two-photon emission, limited only by detector's temporal resolution.

quant-ph↗

arXiv2007

Surface Plasmon Polariton Self-Focusing by Ponderomotive Forces

Nonlinear properties of Surface Plasmon Polaritons stemming from the inherent electron plasma nonlinearity of the metal layers are investigated. A fluid-mechanics plasma model is used to describe the electron motion in metals. The nonlinear ponderomotive force repels the electrons from the high field intensity region, effectively reducing the local plasma frequency and the corresponding real part of the refractive index results in Kerr like self-focusing. The field confinement to the low carrier density region also assists also in reducing the propagation losses, which usually inhibit practical nanoplasmonic circuits. Surface plasmon self focusing and nonlinear spectrum modifications, predicted by our model, are demonstrated by preliminary experiments.

physics.optics↗

arXiv2007

Self-Phasematched Nonlinear Optics in Integrated Semiconductor Microcavities

A novel concept of self-phasematched optical frequency conversion in dispersive dielectric microcavities is studied theoretically and experimentally. We develop a time-dependent model, incorporating the dispersion into the structure of the spatial cavity modes and translating the phasematching requirement into the optimization of a nonlinear cavity mode overlap. We design and fabricate integrated double-resonance semiconductor microcavities for self-phasematched second harmonic generation. The measured efficiency exhibits a significant maximum near the cavity resonance due to the intra-cavity enhancement of the input power and the dispersion-induced wavelength detuning effect on the mode overlap, in good agreement with our theoretical predictions.

physics.optics↗

arXiv2007

High-Rate Entanglement Source via Two-Photon Emission from Semiconductor Quantum Wells

We propose a compact high-intensity room-temperature source of entangled photons based on the efficient second-order process of two-photon spontaneous emission from electrically-pumped semiconductor quantum wells in a photonic microcavity. Two-photon emission rate in room-temperature semiconductor devices is determined solely by the carrier density, regardless of the residual one-photon emission. The microcavity selects two-photon emission for a specific signal and idler wavelengths and at a preferred direction without modifying the overall rate. Pair-generation rate in GaAs/AlGaAs quantum well structure is estimated using a 14-band model to be 3 orders of magnitude higher than for traditional broadband parametric down-conversion sources.

quant-ph↗