P. Degiovanni | École Normale Supérieure de Lyon (original) (raw)

Electron quantum optics by P. Degiovanni

Physical Review B, 2016

Engineering and studying few-electron states in ballistic conductors is a key step towards unders... more Engineering and studying few-electron states in ballistic conductors is a key step towards understanding entanglement in quantum electronic systems. In this Letter, we introduce the intrinsic two-electron coherence of an electronic source in quantum Hall edge channels and relate it to twoelectron wavefunctions and to current noise in an Hanbury Brown-Twiss interferometer. Inspired by the analogy with photon quantum optics, we propose to measure the intrinsic two-electron coherence of a source using low-frequency current correlation measurements at the output of a Franson interferometer. To illustrate this protocol, we discuss how it can distinguish between a time-bin entangled pure state and a statistical mixture of time shifted electron pairs.

Physical Review B, 2008

We consider a model of a detector of ballistic electrons at the edge of a two-dimensional electro... more We consider a model of a detector of ballistic electrons at the edge of a two-dimensional electron gas in the integer quantum Hall regime. The electron is detected by capacitive coupling to a gate which is also coupled to a passive RC circuit. Using a quantum description of this circuit, we determine the signal over noise ratio of the detector in term of the detector characteristics. The back-action of the detector on the incident wavepacket is then computed using a Feynman-Vernon influence functional approach. Using information theory, we define the appropriate notion of quantum limit for such an "on the fly" detector. We show that our particular detector can approach the quantum limit up to logarithms in the ratio of the measurement time over the RC relaxation time. We argue that such a weak logarithmic effect is of no practical significance. Finally we show that a two-electron interference experiment can be used to probe the detector induced decoherence.

Physical Review B, 2010

Inter-edge channel interactions in the quantum Hall regime at filling factor ν = 2 are analyzed w... more Inter-edge channel interactions in the quantum Hall regime at filling factor ν = 2 are analyzed within a plasmon scattering formalism. We derive analytical expressions for energy redistribution amongst edge channels and for high frequency noise, which are shown to fully characterize the low energy plasmon scattering. In the strong interaction limit, the predictions for energy redistribution are compared with recent experimental data and found to reproduce most of the observed features. Quantitative agreement can be achieved by assuming 25% of the injected energy is lost towards other degrees of freedom, possibly the additional gapless excitations predicted for smooth edge potentials.

$Research paper thumbnail of Interactions in quantum Hall edge channels at filling fraction 2$

ABSTRACT Coulomb interactions play a major role in one dimensional electronic transport. They mod... more ABSTRACT Coulomb interactions play a major role in one dimensional electronic transport. They modify the nature of the elementary excitations from Landau quasiparticles in higher dimensions to collective excitations in 1D. We report here on the direct observation of the collective neutral and charge modes of the two chiral co-propagating edge channels of opposite spins of the quantum Hall effect at filling factor ν=2. Generating a charge density wave at frequency f in the outer channel, we measure the current induced by inter-channel Coulomb interaction in the inner channel after a 3 microns propagation length. Varying the driving frequency from 0.7 to 11 GHz, we observe damped oscillations in the induced current that results from the phase shift between the fast charge and slow neutral eigenmodes. Measuring the dispersion relation and dissipation of the neutral mode from provides quantitative information on the scattering of quantum edge magnetoplasmons. We will then comment on the consequences of these results on quasi-particle relaxation and decoherence in the ν=2 quantum Hall edge channel system.

Nature Communications, 2013

Coulomb interactions have a major role in one-dimensional electronic transport. They modify the n... more Coulomb interactions have a major role in one-dimensional electronic transport. They modify the nature of the elementary excitations from Landau quasiparticles in higher dimensions to collective excitations in one dimension. Here we report the direct observation of the collective neutral and charge modes of the two chiral co-propagating edge channels of opposite spins of the quantum Hall effect at filling factor 2. Generating a charge density wave at frequency f in the outer channel, we measure the current induced by inter-channel Coulomb interaction in the inner channel after a 3-μm propagation length. Varying the driving frequency from 0.7 to 11 GHz, we observe damped oscillations in the induced current that result from the phase shift between the fast charge and slow neutral eigenmodes. We measure the dispersion relation and dissipation of the neutral mode from which we deduce quantitative information on the interaction range and parameters.

Physical Review B, 2009

A unified approach to decoherence and relaxation of energy resolved single electron excitations i... more A unified approach to decoherence and relaxation of energy resolved single electron excitations in Integer Quantum Hall edge channels is presented. Within the bosonization framework, relaxation and decoherence induced by interactions and capacitive coupling to an external linear circuit are computed. An explicit connexion with high frequency transport properties of a two terminal device formed by the edge channel on one side and the linear circuit on the other side is established.

New Journal of Physics, 2011

We propose a quantum tomography protocol to measure single electron coherence in quantum Hall edg... more We propose a quantum tomography protocol to measure single electron coherence in quantum Hall edge channels and therefore access for the first time the wave function of single electron excitations propagating in ballistic quantum conductors. Its implementation would open the way to quantitative studies of single electron decoherence and would provide a quantitative tool for analyzing single to few electron sources. We show how this protocol could be implemented using ultrahigh sensitivity noise measurement schemes.

Physical Review Letters, 2012

We have realized a quantum optics like Hanbury Brown and Twiss (HBT) experiment by partitioning, ... more We have realized a quantum optics like Hanbury Brown and Twiss (HBT) experiment by partitioning, on an electronic beam-splitter, single elementary electronic excitations produced one by one by an on-demand emitter. We show that the measurement of the output currents correlations in the HBT geometry provides a direct counting, at the single charge level, of the elementary excitations (electron/hole pairs) generated by the emitter at each cycle. We observe the antibunching of low energy excitations emitted by the source with thermal excitations of the Fermi sea already present in the input leads of the splitter, which suppresses their contribution to the partition noise. This effect is used to probe the energy distribution of the emitted wave-packets.

Physical Review B, 2013

Recent electron quantum optics experiments performed with on-demand single electron sources call ... more Recent electron quantum optics experiments performed with on-demand single electron sources call for a mixed time/frequency approach to electronic quantum coherence. Here, we present a Wigner function representation of first order electronic coherence and show that is provides a natural visualization of the excitations emitted by recently demonstrated single electron sources. It also gives a unified perspective on single particle and two particle interferometry experiments. In particular, we introduce a non-classicality criterion for single electron coherence and discuss it in the context of Mach-Zenhder interferometry. Finally, the electronic Hanbury Brown and Twiss and the Hong Ou Mandel experiments are interpreted in terms of overlaps of Wigner function thus connecting them to signal processing.

$Research paper thumbnail of Integer and fractional charge Lorentzian voltage pulses analyzed in the framework of photon-assisted shot noise$

Science, 2013

The on-demand emission of coherent and indistinguishable electrons by independent synchronized so... more The on-demand emission of coherent and indistinguishable electrons by independent synchronized sources is a challenging task of quantum electronics, in particular regarding its application for quantum information processing. Using two independent on-demand electron sources, we trigger the emission of two single-electron wavepackets at different inputs of an electronic beamsplitter. Whereas classical particles would be randomly partitioned by the splitter, we observe two-particle interferences resulting from quantum exchange.

ABSTRACT The ballistic propagation of electronic waves in the quantum Hall edge channels of a 2DE... more ABSTRACT The ballistic propagation of electronic waves in the quantum Hall edge channels of a 2DEG bears strong analogies with photon optics which inspired a whole set of experiments, including the realization of electronic Mach-Zehnder [1] and Hanbury-Brown and Twiss [2] interferometers. So far, these experiments have been performed with continuous sources, but the recent realization of on-demand single electron emitters [3] has risen the hope to reach, in these experiments, the single charge control. We report here on the first realization of a Hanbury-Brown and Twiss experiment on a single electron beam generated by the single electron emitter recently developed by our group [3]. Using the chiral edge channels of the quantum Hall effect, single electron emitted by the source are directed towards an electronic beam-splitter. From the low frequency current correlations at the output of the beam splitter, we are able to count and characterize the elementary excitations produced by the source. By analyzing their antibunching with thermal excitations, we show that we are able to shape single particle states in a tuneable way. [1] Ji et al., Nature 422, 415 (2003) [2] Henny et al., Science 284 296 (1999) [3] Fève et al., Science 316, 1169 (2007)

Physical Review Letters, 2014

Quantum Hall edge channels at integer filling factor provide a unique test-bench to understand de... more Quantum Hall edge channels at integer filling factor provide a unique test-bench to understand decoherence and relaxation of single electronic excitations in a ballistic quantum conductor. In this Letter, we obtain a full visualization of the decoherence scenario of energy (Landau) and time (Levitov) resolved single electron excitations at filling factor ν = 2. We show that the Landau excitation exhibits a fast relaxation followed by spin-charge separation whereas the Levitov excitation only experiences spin-charge separation. We finally suggest to use Hong-Ou-Mandel type experiments to probe specific signatures of these different scenarios.

Quantum transport by P. Degiovanni

Journal of Applied Physics, 2014

ABSTRACT We present an experimental study of the low frequency admittance of quantum Hall conduct... more ABSTRACT We present an experimental study of the low frequency admittance of quantum Hall conductors in the [100 Hz, 1 MHz] frequency range. We show that the frequency dependence of the admittance of the sample strongly depends on the topology of the contacts connections. Our experimental results are well explained within the Christen and Büttiker approach for finite frequency transport in quantum Hall edge channels taking into account the influence of the coaxial cables capacitance. In the Hall bar geometry, we demonstrate that there exists a configuration in which the cable capacitance does not influence the admittance measurement of the sample. In this case, we measure the electrochemical capacitance of the sample and observe its dependence on the filling factor.

International Journal of Nanotechnology, 2010

The time τ φ over which an electron can maintain its phase coherence at low temperatures is of fu... more The time τ φ over which an electron can maintain its phase coherence at low temperatures is of fundamental importance in mesoscopic systems. The observability of many phenomena, such as the Aharonov Bohm effect, the universal conductance fluctuations, the weak localisation correction to the conductance, persistent current in ringstructures and many more rely on a long enough phase coherence time. In disordered conductors and within the standard Fermi liquid picture, the phase coherence time is expected to diverge at zero temperature. However, most experiments show a saturating phase coherence time at low temperatures. This saturation has often been attributed to the presence of a small amount of magnetic impurities giving rise to the so-called Kondo effect. In this paper, we present a brief review of recent advances, both experimental and theoretical, in the understanding of dephasing by magnetic impurities in the framework of the Kondo effect. . Their work concerns quantum coherence in Kondo systems and spin glasses, Kondo effect in semiconductor nanostructures and more recently spin based quantum bits and nanomechanics. The group has good expertise in very low temperature physics under high magnetic field, ultra-low noise transport measurements and micro-SQUID magnetometry.

Physica E: Low-dimensional Systems and Nanostructures, 2007

We review recent experimental progress on the saturation problem in metallic quantum wires. In pa... more We review recent experimental progress on the saturation problem in metallic quantum wires. In particular, we address the influence of magnetic impurities on the electron phase coherence time. We also present new measurements of the phase coherence time in ultra-clean gold and silver wires and analyse the saturation of τ φ in these samples, cognizant of the role of magnetic scattering. For the cleanest samples, Kondo temperatures below 1 mK and extremely-small magnetic-impurity concentration levels of less than 0.08 ppm have to be assumed to attribute the observed saturation to the presence of magnetic impurities.

Decoherence of solid state and atomic systems by P. Degiovanni

Motivated by recent experiments with Josephson qubits we propose a new phenomenological model for... more Motivated by recent experiments with Josephson qubits we propose a new phenomenological model for /f noise due to collective excitations of interacting defects in the qubit's environment. At very low temperatures the effective dynamics of these collective modes are very slow leading to pronounced non-Gaussian features and nonstationarity of the noise. We analyze the influence of this noise on the dynamics of a qubit in various regimes and at different operation points. Remarkable predictions are absolute time dependences of a critical coupling and of dephasing in the strong coupling regime.

Physical Review B, 2016

Physical Review B, 2008

Physical Review B, 2010

$Research paper thumbnail of Interactions in quantum Hall edge channels at filling fraction 2$

Nature Communications, 2013

Physical Review B, 2009

New Journal of Physics, 2011

Physical Review Letters, 2012

Physical Review B, 2013

$Research paper thumbnail of Integer and fractional charge Lorentzian voltage pulses analyzed in the framework of photon-assisted shot noise$

Science, 2013

Physical Review Letters, 2014

Journal of Applied Physics, 2014

International Journal of Nanotechnology, 2010

Physica E: Low-dimensional Systems and Nanostructures, 2007

Physical Review B, 2000

Schrődinger cat states built from quantum superpositions of left or right Luttinger fermions loca... more Schrődinger cat states built from quantum superpositions of left or right Luttinger fermions located at different positions in a spinless Luttinger liquid are considered. Their decoherence rates are computed within the bosonization approach using as environments the quantum electromagnetic field or two or three dimensional acoustic phonon baths. Emphasis is put on the differences between the electromagnetic and acoustic environments.

The European Physical Journal D, 2008

We investigate the behavior of a circuit QED device when the resonator is initially populated wit... more We investigate the behavior of a circuit QED device when the resonator is initially populated with a mesoscopic coherent field. The strong coupling between the cavity and the qubit produces an entangled state involving mesoscopic quasi-pointer states with respect to cavity dissipation. The overlap of the associated field components results in collapse and revivals for the Rabi oscillation. Although qubit relaxation and dephasing do not preserve these states, a simple analytical description of the dissipative dynamics of the circuit QED device including cavity relaxation as well as qubit dissipation is obtained from the Monte-Carlo approach. Explicit predictions for the spontaneous and induced Rabi oscillation signals are derived and sucessfully compared with exact calculations. We show that these interesting effects could be observed with a 10 photon field in forthcoming circuit QED experiments.

Europhysics Letters (EPL), 2005

PACS. 03.65.Yz -First pacs description. PACS. 73.23.-b -Second pacs description.

Physical Review A, 2006

We investigate the behavior of N atoms resonantly coupled to a single electromagnetic field mode ... more We investigate the behavior of N atoms resonantly coupled to a single electromagnetic field mode sustained by a high quality cavity, containing a mesoscopic coherent field. We show with a simple effective hamiltonian model that the strong coupling between the cavity and the atoms produces an atom-field entangled state, involving N + 1 nearly-coherent components slowly rotating at different paces in the phase plane. The periodic overlap of these components results in a complex collapse and revival pattern for the Rabi oscillation. We study the influence of decoherence due to the finite cavity quality factor. We propose a simple analytical model, based on the Monte Carlo approach to relaxation. We compare its predictions with exact calculations and show that these interesting effects could realistically be observed on a two or three atoms sample in a 15 photons field with circular Rydberg atoms and superconducting cavities.

Physical Review B, 2005

We consider a new phenomenological model for a 1/f µ classical intermittent noise and study its e... more We consider a new phenomenological model for a 1/f µ classical intermittent noise and study its effects on the dephasing of a two-level system. Within this model, the evolution of the relative phase between the |± states is described as a continuous time random walk (CTRW). Using renewal theory, we find exact expressions for the dephasing factor and identify the physically relevant various regimes in terms of the coupling to the noise. In particular, we point out the consequences of the non-stationarity and pronounced non-Gaussian features of this noise, including some new anomalous and aging dephasing scenarii.

Theoretical and Mathematical Physics, 1998

We present a comprehensive study of the effective Conformal Field Theory (CFT) describing the low... more We present a comprehensive study of the effective Conformal Field Theory (CFT) describing the low energy excitations of a gas of spinless interacting fermions on a circle in the gapless regime (Luttinger liquid). Functional techniques and modular transformation properties are used to compute all correlation functions in a finite size and at finite temperature. Forward scattering disorder is treated exactly. Laughlin experiments on charge transport in a Quantum Hall Fluid on a cylinder are reviewed within this CFT framework. Edge excitations above a given bulk excitation are described by a twisted version of the Luttinger effective theory. Luttinger CFTs corresponding to the ν = 1/(2p + 1) filling fractions appear to be rational CFTs (RCFT). Generators of the extended symmetry algebra are identified as edge fermions creators and annihilators, thus giving a physical meaning to the RCFT point of view on edge excitations of these sequences.

Communications in Mathematical Physics, 1992

We prove that any solution to Moore and Seiberg's equations defines a Projective Rational Topolog... more We prove that any solution to Moore and Seiberg's equations defines a Projective Rational Topological Field Theory (PRTFT) using surgery presentations for decorated three-manifolds and Kirby's calculus.

Communications in Mathematical Physics, 1990

We compute the modular properties of the possible genus-one characters of some Rational Conformal... more We compute the modular properties of the possible genus-one characters of some Rational Conformal Field Theories starting from their fusion rules. We show that the possible choices of S matrices are indexed by some automorphisms of the fusion algebra. We also classify the modular invariant partition functions of these theories. This gives the complete list of modular invariant partition functions of Rational Conformal Field Theories with respect to the Aff level one algebra.

Nature Nanotechnology, 2008

Electrons and other fundamental particles have an intrinsic angular momentum called spin. A chang... more Electrons and other fundamental particles have an intrinsic angular momentum called spin. A change in the spin state of such a particle is therefore equivalent to a mechanical torque. This spin-induced torque is central to our understanding of experiments 1,2 ranging from the measurement of the angular momentum of photons 3 and the g-factor of metals 4-7 to magnetic resonance 8 and magnetization reversal in magnetic multilayers . When a spin-polarized current passes through a metallic nanowire in which one half is ferromagnetic and the other half is nonmagnetic, the spins of the itinerant electrons are 'flipped' at the interface between the two regions to produces a torque. Here, we report direct measurement of this mechanical torque in an integrated nanoscale torsion oscillator, and measurements of the itinerant electron spin polarization that could yield new information on the itinerancy of the d-band electrons. The unprecedented torque sensitivity of 1 3 10 222 N-m Hz 21/2 may have applications in spintronics and precision measurements of charge-parityviolating forces , and might also enable experiments on the untwisting of DNA 18 and torque-generating molecules .

Nature Nanotechnology, 2008

Europhysics Letters (EPL), 2004

physica status solidi (b), 2017

The recent developments of electron quantum optics in quantum Hall edge channels have given us ne... more The recent developments of electron quantum optics in quantum Hall edge channels have given us new ways to probe the behavior of electrons in quantum conductors. It has brought new quantities called electronic coherences under the spotlight. In this paper, we explore the relations between electron quantum optics and signal processing through a global review of the various methods for accessing single-and two-electron coherences in electron quantum optics. We interpret electron quantum optics interference experiments as analog signal processing, converting quantum signals into experimentally observable quantities such as current averages and correlations. This point of view also gives us a procedure to obtain quantum information quantities from electron quantum optics coherences. We illustrate these ideas by discussing two-mode entanglement in electron quantum optics. We also sketch how signal processing ideas may open new perspectives for representing electronic coherences in quantum conductors and understand the properties of the underlying many-body electronic state.

physica status solidi (b), 2016

Since the pioneering works of Hanbury-Brown and Twiss, intensity-intensity correlations have been... more Since the pioneering works of Hanbury-Brown and Twiss, intensity-intensity correlations have been widely used in astronomical systems, for example, to detect binary stars. They reveal statistics effects and two-particle interference, and offer a decoherence-free probe of the coherence properties of light sources. In the quantum Hall edge channels, the concept of quantum optics can be transposed to electrons, and an analogous two-particle interferometry can be developed, in order to characterize single-electron states. We review in this article the recent experimental and theoretical progress on this topic.

Using its Conformal Field Theory description, the Luttinger liquid is coupled to the quantum elec... more Using its Conformal Field Theory description, the Luttinger liquid is coupled to the quantum electromagnetic field. We compute the decoherence properties of a superposition of two states obtained by creating the same elementary excitation at different places in the system. a It means that backscattering terms which can potentially open a gap in the spectrum are discarded. For an annular FQH fluid, the two edges sufficiently separated and backscattering is strongly suppressed.

Physical Review Letters, 2012

Nuclear Physics B - Proceedings Supplements, 1988

clicking here. colleagues, clients, or customers by , you can order high-quality copies for your ... more clicking here. colleagues, clients, or customers by , you can order high-quality copies for your If you wish to distribute this article to others here. following the guidelines can be obtained by Permission to republish or repurpose articles or portions of articles ): February 28, 2013 www.sciencemag.org (this information is current as of The following resources related to this article are available online at http://www.sciencemag.org/content/339/6123/1054.full.html version of this article at: including high-resolution figures, can be found in the online Updated information and services, http://www.sciencemag.org/content/339/6123/1054.full.html#related found at: can be related to this article A list of selected additional articles on the Science Web sites http://www.sciencemag.org/content/339/6123/1054.full.html#ref-list-1 , 3 of which can be accessed free: cites 27 articles This article http://www.sciencemag.org/cgi/collection/physics Physics subject collections: This article appea...

arXiv: Mesoscale and Nanoscale Physics, 2002

We derive non equilibrium statistical ensembles for a ballistic Aharonov-Bohm loop connected to s... more We derive non equilibrium statistical ensembles for a ballistic Aharonov-Bohm loop connected to several electrodes connected to reservoirs with different chemical potentials. A striking consequence of these non trivial ensembles is the emergence of quantum zero point fluctuations of the persistent current around the loop. Detailed predictions for the low frequency noise power are given.

Although interesting per se, decoherence and relaxation of single-electron excitations induced by... more Although interesting per se, decoherence and relaxation of single-electron excitations induced by strong effective screened Coulomb interactions in Quantum Hall edge channels are an important challenge for the applications of electron quantum optics in quantum information and quantum sensing. In this paper, we study intrinsic single-electron decoherence within an ideal single-electron channel with long-range effective Coulomb interactions to determine the influence of the material and sample properties. We find that weak-coupling materials characterized by a high velocity of hot-electron excitations may offer interesting perspectives for limiting intrinsic decoherence due to electron/electron interactions. We discuss quantitively how extrinsic decoherence due to the coupling with the channel’s electromagnetic environment can be efficiently inhibited in specially designed samples at ν = 2 with one closed edge channel and we propose a realistic geometry for testing decoherence control...

New Journal of Physics, 2011

Nature Communications

In quantum nanoelectronics, time-dependent electrical currents are built from few elementary exci... more In quantum nanoelectronics, time-dependent electrical currents are built from few elementary excitations emitted with well-defined wavefunctions. However, despite the realization of sources generating quantized numbers of excitations, and despite the development of the theoretical framework of time-dependent quantum electronics, extracting electron and hole wavefunctions from electrical currents has so far remained out of reach, both at the theoretical and experimental levels. In this work, we demonstrate a quantum tomography protocol which extracts the generated electron and hole wavefunctions and their emission probabilities from any electrical current. It combines two-particle interferometry with signal processing. Using our technique, we extract the wavefunctions generated by trains of Lorentzian pulses carrying one or two electrons. By demonstrating the synthesis and complete characterization of electronic wavefunctions in conductors, this work offers perspectives for quantum information processing with electrical currents and for investigating basic quantum physics in many-body systems.

Physical Review B, 2016

Depuis la fin du xxe siècle, la théorie quantique connaît un renouveau qui se traduit par l’émerg... more Depuis la fin du xxe siècle, la théorie quantique connaît un renouveau qui se traduit par l’émergence de technologies utilisant toute la puissance des interférences quantiques pour mesurer, simuler, communiquer et calculer.

Parallèlement, cette « seconde révolution quantique » remet en question notre compréhension de la théorie quantique et nous pousse à dépasser la vision purement utilitariste de l’interprétation de Copenhague.
part, il vise à utiliser cette exploration pour éclairer le sens de la théorie quantique en insistant sur l’absence d’état objectif défini sans référence à un observateur. Il s’agit du premier (et seul) ouvrage qui présente une synthèse de l’ensemble de ces sujets.

Cet ouvrage a donc un double objectif : d’une part il donne une introduction globale au domaine des technologies quantiques en présentant les relations entre théorie quantique, théorie de l’information et informatique ; d’autre part, il vise à éclairer le sens de la théorie quantique en se focalisant sur la notion d’état quantique. L’ensemble de ces sujets est présenté en une synthèse originale.

Ce premier volume offre au lecteur, qu’il soit physicien, ingénieur, mathématicien ou informaticien, de se fami- liariser avec les technologies quantiques. Une discussion des systèmes d’électrodynamique en cavité : atomes en cavité et aussi circuits supraconducteurs, illustre concrètement nombre d’idées et méthodes.