## About

71

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Introduction

In the team "Quantum Physics in Circuits", we explore the quantum phenomena in nano-scale electronic circuits.
We investigate a broad spectrum of fundamental physics, from correlated electronic matter to quantum transport at the most elementary level of the single conduction channel.
For this purpose, the devices fabricated in the lab's large facilities are measured down to extremely low electronic temperatures (6 mK) with ultra-sensitive setups.
https://qpc.c2n.universite-paris-saclay.fr

## Publications

Publications (71)

The Kondo effect, deriving from a local magnetic impurity mediating electron-electron interactions, constitutes a flourishing basis for understanding a large variety of intricate many-body problems. Its experimental implementation in tunable circuits has made possible important advances through well-controlled investigations. However, these have mo...

Recent pioneering works have set the stage for exploring anyon braiding statistics from negative current cross-correlations along two intersecting quasiparticle beams. In such a dual-source-analyzer quantum point contact setup, also referred to as “collider,” the anyon exchange phase of fractional quantum Hall quasiparticles is predicted to be impr...

The scattering of exotic quasiparticles may follow different rules than electrons. In the fractional quantum Hall regime, a quantum point contact (QPC) provides a source of quasiparticles with field effect selectable charges and statistics, which can be scattered on an ‘analyzer’ QPC to investigate these rules. Remarkably, for incident quasiparticl...

Recent pioneering works have set the stage for exploring anyon braiding statistics from negative current cross-correlations along two intersecting quasiparticle beams. In such a dual-source - analyzer quantum point contact setup, also referred to as 'collider', the anyon exchange phase of fractional quantum Hall quasiparticles is predicted to be im...

We observe and comprehend the dynamical Coulomb blockade suppression of the electrical conductance across an electronic quantum channel subjected to a temperature difference. A broadly tunable, spin-polarized Ga(Al)As quantum channel is connected on-chip, through a micron-scale metallic node, to a linear RC circuit. The latter is made up of the nod...

We observe and comprehend the dynamical Coulomb blockade suppression of the electrical conductance across an electronic quantum channel submitted to a temperature difference. A broadly tunable, spin-polarized Ga(Al)As quantum channel is connected on-chip, through a micron-scale metallic node, to a linear $RC$ circuit. The latter is made up of the n...

When assembling individual quantum components into a mesoscopic circuit, the interplay between Coulomb interaction and charge granularity breaks down the classical laws of electrical impedance composition. Here we explore experimentally the thermal consequences, and observe an additional quantum mechanism of electronic heat transport. The investiga...

When assembling individual quantum components into a mesoscopic circuit, the interplay between Coulomb interaction and charge granularity breaks down the classical laws of electrical impedance composition. Here we explore experimentally the thermal consequences, and observe an additional quantum mechanism of electronic heat transport. The investiga...

Transmitting quantum states
The coherence of electrons in mesoscopic structures is thought to be unlikely to survive in a disordered environment. Duprez et al. show that this is not necessarily the case. They studied a metallic island as an example of a disordered environment. They made an electron interferometer and incorporated the island in one...

The quantum coherence of electronic quasiparticles underpins many of the emerging transport properties of conductors at small scales. Novel electronic implementations of quantum optics devices are now available with perspectives such as “flying-qubit” manipulations. However, electronic quantum interferences in conductors remained up to now limited...

The quantum coherence of electronic quasiparticles underpins many of the emerging transport properties of conductors at small scales. Novel electronic implementations of quantum optics devices are now available with perspectives such as 'flying' qubit manipulations. However, electronic quantum interferences in conductors remained up to now limited...

The Coulomb interaction generally limits the quantum propagation of electrons. However, it can also provide a mechanism to transfer their quantum state over larger distances. Here, we demonstrate such a form of teleportation, across a metallic island within which the electrons are trapped much longer than their quantum lifetime. This effect origina...

The Tomonaga-Luttinger liquid (TLL) concept is believed to generically describe the strongly correlated physics of one-dimensional systems at low temperatures. A hallmark signature in 1D conductors is the quantum phase transition between metallic and insulating states induced by a single impurity. However, this transition impedes experimental explo...

A nanostructure quantum simulator
Phase transitions occurring at absolute zero temperature, or quantum phase transitions (QPTs), can be grouped into broad categories called universality classes. The classification is based on the properties of the transition rather than the microscopic details of the underlying system. Iftikhar et al. exploited thi...

Quantum mechanics and Coulomb interaction dictate the behaviour of small circuits. The thermal implications cover fundamental topics from quantum control of heat to quantum thermodynamics, with prospects of novel thermal machines and an ineluctably growing influence on nanocircuit engineering. Experimentally, the rare observations thus far include...

Quantum physics emerge and develop as temperature is reduced. Although mesoscopic electrical circuits constitute an outstanding platform to explore quantum behaviour, the challenge in cooling the electrons impedes their potential. The strong coupling of such micrometre-scale devices with the measurement lines, combined with the weak coupling to the...

Supplementary Figures 1-3 and Supplementary Notes 1-2

In 1909, Millikan showed that the charge of electrically isolated systems is quantized in units of the elementary electron charge e. Today, the persistence of charge quantization in small, weakly connected conductors allows for circuits in which single electrons are manipulated, with applications in, for example, metrology, detectors and thermometr...

Many-body correlations and macroscopic quantum behaviours are fascinating condensed matter problems. A powerful test-bed for the many-body concepts and methods is the Kondo effect, which entails the coupling of a quantum impurity to a continuum of states. It is central in highly correlated systems and can be explored with tunable nanostructures. Al...

Quantum physics predicts that there is a fundamental maximum heat conductance
across a single transport channel, and that this thermal conductance quantum
$G_Q$ is universal, independent of the type of particles carrying the heat.
Such universality, combined with the relationship between heat and information,
signals a general limit on information...

In one-dimensional conductors, interactions result in correlated electronic systems. At low energy, a hallmark signature of the so-called Tomonaga-Luttinger liquids is the universal conductance curve predicted in presence of an impurity. A seemingly different topic is the quantum laws of electricity, when distinct quantum conductors are assembled i...

Supplementary Figures S1-S6, Supplementary Notes S1-S9 and Supplementary References

We demonstrate a direct approach to investigate heat transport in the fractional quantum Hall regime. At a filling factor of ν=4/3, we inject power at quantum point contacts and detect the related heating from the activated current through a quantum dot. The experiment reveals a chargeless heat transport from a significant heating that occurs upstr...

We present an experiment where the quantum coherence in the edge states of
the integer quantum Hall regime is tuned with a decoupling gate. The coherence
length is determined by measuring the visibility of quantum interferences in a
Mach-Zehnder interferometer as a function of temperature, in the quantum Hall
regime at filling factor two. The tempe...

What are the quantum laws of electricity in mesoscopic circuits? This very
fundamental question has also direct implications for the quantum engineering
of nanoelectronic devices. Indeed, when a quantum coherent conductor is
inserted into a circuit, its transport properties are modified. In particular,
its conductance is reduced because of the circ...

The chiral edge channels in the quantum Hall regime are considered ideal ballistic quantum channels, and have quantum information processing potentialities. Here, we demonstrate experimentally, at a filling factor of ν(L)=2, the efficient tuning of the energy relaxation that limits quantum coherence and permits the return toward equilibrium. Energy...

We investigate the energy exchanges along an electronic quantum channel realized in the integer quantum Hall regime at a filling factor of νL=2. One of the two edge channels is driven out of equilibrium and the resulting electronic energy distribution is measured in the outer channel, after several propagation lengths 0.8 μm≤L≤30 μm. Whereas ther...

Les porteurs de charge dans les conducteurs électriques sont généralement bien décrits par des particules électroniques pratiquement libres malgré l’interaction de Coulomb. Ce n’est pas le cas dans les conducteurs unidimensionnels où l’effet des interactions est exacerbé par le confinement et où des phénomènes spectaculaires comme la séparation du...

Inter-edge channel interactions in the quantum Hall regime at filling factor nu= 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...

Heat transport has large potentialities to unveil new physics in mesoscopic
systems. A striking illustration is the integer quantum Hall regime, where the
robustness of Hall currents limits information accessible from charge
transport. Consequently, the gapless edge excitations are incompletely
understood. The effective edge states theory describes...

A two-dimensional electron system without spatial inversion symmetry develops a sample specific dc voltage when exposed to a microwave radiation at low temperature. We investigate this photovoltaic (PV) effect in the case where spatial symmetry is broken by an evanescent high-frequency potential. We measure the induced PV voltage in a GaAs/Ga1−xAlx...

Whereas electrical noise has been extensively studied at low frequency in various systems, going from macroscopic to mesoscopic scales, and is now relatively well understood, investigation of high frequency noise is much more recent and raises new physical problems which could not be addressed before. Of particular interest is the frequency range o...

We report the results of several nonequilibrium experiments performed on superconducting/normal/superconducting (S/N/S) Josephson junctions containing either one or two extra terminals that connect to normal reservoirs. Currents injected into the junctions from the normal reservoirs induce changes in the electron energy distribution function, which...

We observed the recently predicted quantum suppression of dynamical Coulomb blockade on short coherent conductors by measuring the conductance of a quantum point contact embedded in a tunable on-chip circuit. Taking advantage of the circuit modularity we measured most parameters used by the theory. This allowed us to perform a reliable and quantita...

Multicontact transport measurements were performed on a superconducting tin nanowire to probe its local properties and especially the formation of phase-slip centers (PSCs). We find that normal metal contacts strongly disturb the behavior of the nanowire. In particular, they provide an efficient escape way for the energy dissipated at the PSC and t...

We report an experiment on the determination of the quantum nondemolition (QND) nature of a readout scheme of a quantum electrical circuit. The circuit is a superconducting quantum bit measured by microwave reflectometry using a Josephson bifurcation amplifier. We perform a series of two subsequent measurements, record their values and correlation,...

We measure the high-frequency emission of a single Cooper pair transistor (SCPT) in the regime where transport is only due to tunneling of Cooper pairs. This is achieved by coupling on chip the SCPT to a superconductor-insulator-superconductor junction and by measuring the photon assisted tunneling current of quasiparticles across the junction. Thi...

A single-Cooper-pair transistor (SCPT) is coupled capacitively to a voltage biased Josephson junction, used as a high-frequency generator. Thanks to the high energy of photons generated by the Josephson junction, transitions between energy levels, not limited to the first two levels, were induced and the effect of this irradiation on the dc Josephs...

Mesoscopic transport measurements reveal a large effective phase coherence
length in epitaxial GaMnAs ferromagnets, contrary to usual 3d-metal
ferromagnets. Universal conductance fluctuations of single nanowires are
compared for epilayers with a tailored anisotropy. At large magnetic fields,
quantum interferences are due to structural disorder only...

We measure current fluctuations of mesoscopic devices in the quantum regime, when the frequency is of the order of or higher than the applied voltage or temperature. Detection is designed to probe separately the absorption and emission contributions of current fluctuations, i.e. the positive and negative frequencies of the Fourier transformed nonsy...

We have constructed a new type of amplifier whose primary purpose is the readout of superconducting quantum bits. It is based on the transition of an RF-driven Josephson junction between two distinct oscillation states near a dynamical bifurcation point. The main advantages of this new amplifier are speed, high-sensitivity, low back-action, and the...

We performed a novel phase-sensitive microwave reflection experiment which directly probes the dynamics of the Josephson plasma resonance in both the linear and the nonlinear regime. When the junction was driven below the plasma frequency into the nonlinear regime, we observed for the first time the transition between two different dynamical states...

We have constructed a new type of amplifier whose primary purpose is the readout of superconducting quantum bits. It is based on the transition of a rf-driven Josephson junction between two distinct oscillation states near a dynamical bifurcation point. The main advantages of this new amplifier are speed, high sensitivity, low backaction, and the a...

The energy dependence and intensity of Coulomb interaction between quasiparticles in metallic wires is obtained from two different methods: determination of the temperature dependence of the phase coherence time from the magnetoresistance, and measurements of the energy distribution function in out-of-equilibrium situations. In both types of experi...

We have developed a novel amplifier based on the switching between two dynamical states of a capacitively-shunted, driven Josephson junction. This non-linear oscillator is biased near a Hopf bifurcation with an amplitude modulated monochromatic microwave drive signal. The two dynamical states differ in their oscillation phase and can be readily dis...

We present first measurements of a new, high-sensitivity amplifier for
the readout of superconducting quantum bits. It is based on the
dynamical switching of a Josephson junction driven by RF pulses from a
low-amplitude to a high-amplitude oscillation state. A convenient
signature of this transition is a change in phase of the reflected drive
signa...

The low-temperature behavior of the electron phase coherence time, τφ, in mesoscopic metal wires has been a subject of controversy recently. Whereas theory predicts that τφ(T) in narrow wires should increase as T
−2/3 as the temperature T is lowered, many samples exhibit a saturation of τφ below about 1 K. We review here the experiments we have per...

We performed a novel phase sensitive microwave reflection experiment which directly probes the dynamics of the Josephson plasma resonance in both the linear and non-linear regime. When the junction was driven below the plasma frequency into the non-linear regime, we observed for the first time the transition between two different dynamical states p...

We have extracted the phase coherence time $\tau_{\phi}$ of electronic quasiparticles from the low field magnetoresistance of weakly disordered wires made of silver, copper and gold. In samples fabricated using our purest silver and gold sources, $\tau_{\phi}$ increases as $T^{-2/3}$ when the temperature $T$ is reduced, as predicted by the theory o...

In order to find out if magnetic impurities can mediate interactions between quasiparticles in metals, we have measured the effect of a magnetic field B on the energy distribution function f(E) of quasiparticles in two silver wires driven out of equilibrium by a bias voltage U. In a sample showing sharp distributions at B=0, no magnetic field effec...

By controlling the distribution function within the normal metal of a superconductor/normal metal/superconductor (SNS)Josephson junction, one can reverse the direction of the supercurrent, creating a pi-state [1]. This manipulation may be done by injecting a quasiparticle current into the normal metal from one or more normal reservoirs [2]. In the...

We are developing a new scheme employing microwave pulses for fast, single-shot readout of a superconducting charge-phase qubit [1]. The qubit consists of a Cooper-pair transistor in parallel with a large Josephson junction. The critical current of this combined junction system changes by about 1 amplify this signal by current biasing the large jun...

The low temperature behavior of the electron phase coherence time in metals, τ φ , is currently a subject of controversy. While theory predicts that τ φ should increase on cooling as an inverse power law of temperature, many samples exhibit a saturation of τ φ below a temperature between 0.1 and 1 K. In this paper we present evidence that the satur...

Phase-coherent electron transport in metals and semiconductors forms the basis of the fleld called "mesoscopic physics." Underpinning this fleld are two concepts that became widely appreciated in the 1980's: flrst, static disorder does not destroy phase coherence of conduction electrons, hence quantum interference phenomena are observable even in h...

We have probed the magnetic field dependence of the electron phase coherence time tau(phi) by measuring the Aharonov-Bohm conductance oscillations of mesoscopic Cu rings. Whereas tau(phi) determined from the low-field magnetoresistance saturates below 1 K, the amplitude of Aharonov-Bohm h/e oscillations increases strongly on a magnetic field scale...

Recently Baselmans et al. [Nature, 397, 43 (1999)] showed that the direction of the supercurrent in a superconductor/normal/superconductor Josephson junction can be reversed by applying, perpendicularly to the supercurrent, a sufficiently large control current between two normal reservoirs. The novel behavior of their 4-terminal device (called a co...

We have measured in a copper wire the energy exchange rate between quasiparticles as a function of the applied magnetic field. We find that the effective electron-electron interaction is strongly modified by the magnetic field, suggesting that magnetic impurities play a role on the interaction processes.

We have measured the differential conductance of a tunnel junction between a thin metallic wire and a thick ground plane, as a function of the applied voltage. We find that near zero voltage, the differential conductance exhibits a dip, which scales as 1/square root of [V] down to voltages V approximately 10k(B)T/e. The precise voltage and temperat...

We have performed the tunnel spectroscopy of the energy distribution function of quasiparticles in 5-microm-long silver wires connected to superconducting reservoirs biased at different potentials. The distribution function f(E) presents several steps, which are manifestations of multiple Andreev reflections at the NS interfaces. The rounding of th...

We have measured the phase coherence time, tau_phi, in mesoscopic wires of Au, Ag, and Cu, over the temperature range 40 mK-6 K. (A.B. Gougam et al., J. Low Temp. Phys.) 118, 447 (2000). In Ag wires, as well as one Au wire made from six 9's purity Au, tau_phi increases down to the lowest temperatures measured, as predicted by the theory of electron...

We have measured in gold wires the energy exchange rate between quasiparticles, the phase coherence time of quasiparticles and the resistance vs. temperature, in order to probe the interaction processes which are relevant at low temperatures. We find that the energy exchange rate is higher than expected from the theory of electron-electron interact...