arXiv subjects

Bertrand Reulet

Publications and source records attributed to Bertrand Reulet.

At least 37 records · Page 2Linked to original sources

arXiv2021

Photocount statistics of the Josephson parametric amplifier: a question of detection

Parametric amplifiers are known to squeeze the vacuum state of the electromagnetic field, which results in predictable statistics of the photocounts at their output. However, recent theoretical work arXiv:1112.4159 predicts a very different statistical distribution for an amplifier based on a Josephson junction. We test the hypothesis experimentally and recover the expected squeezed vacuum statistics. We explain this discrepancy by showing theoretically how the photocount statistics is dictated by the detection process, from single mode (our experiment) to multimode, fully resolved in frequency (as in arXiv:1112.4159).

quant-ph↗

arXiv2020

Noise feedback in an electronic circuit

Electronic circuits are built by combining components with known current/voltage characteristics, which are intrinsic to each component and independent of the rest of the circuit. This approach breaks down for nanostructures placed at ultra-low temperature, a phenomenon referred to as Dynamical Coulomb Blockade, and usually attributed to quantum effects. Here we report similar phenomena on a simple circuit at room temperature, devoid of any quantum features: an avalanche diode in series with a resistor, where the current/voltage characteristics of the diode depends strongly on the value of the resistor. We show that the key ingredient for this is the feedback of the noise of the component on itself through the rest of the circuit. Moreover, we have developed a theory that links transport and noise in the presence of an external electromagnetic environment, which explains very well our experimental results.

cond-mat.mes-hall↗

arXiv2020

Quantitative Measurements of Giant and Quantized Microwave Faraday Rotation

We report {\it quantitative} microwave Faraday rotation measurements conducted with a high-mobility two-dimensional electron gas (2DEG) in a GaAs/AlGaAs semiconductor heterostructure. In a magnetic field, the Hall effect and the Faraday effect arise from the action of Lorentz force on electrons in the 2DEG. As with the Hall effect, a classical Faraday effect is observed at low magnetic field as well as a quantized Faraday effect at high magnetic field. The high electron mobility of the 2DEG enables a giant single-pass Faraday rotation of $θ_F^{max} \simeq 45^\circ$ $(\simeq0.8$~rad) to be achieved at a modest magnetic field of $B \simeq 100$~mT. In the quantum regime, we find that the Faraday rotation $θ_F$ is quantized in units of $α^*= 2.80(4)α$, where $α\simeq 1/137$ is the fine structure constant. The enhancement in rotation quantum $α^* > α$ is attributed to electromagnetic confinement within a waveguide structure.

cond-mat.mes-hall↗

arXiv2020

Dynamical I-V Characteristics of SNS Junctions

We have probed the switching dynamics of the Josephson critical current of a superconducting weak link by measuring its voltage/current characteristics while applying an ac current bias in the range 1-200 MHz. The weak link between two Nb reservoirs is formed by an mesoscopic Al wire above its critical temperature. We observe a dynamical phase transition as a function of the frequency and amplitude of the ac current. While at low frequency the transition driven by increasing the current bias is well described by the standard Kramers theory, at high frequency the switching histograms become hysteretic and much narrower than expected by thermal fluctuations. The crossover frequency between the two regimes is set by the electron-phonon interaction rate in the normal metal.

cond-mat.mes-hall↗

arXiv2020

Shot Noise of a Temperature-Biased Tunnel Junction

We report the measurement of the current noise of a tunnel junction driven out-of-equilibrium by a temperature and/or voltage difference, i.e. the charge noise of heat and/or electrical current. This is achieved by a careful control of electron temperature below 1 K at the nanoscale, and a sensitive measurement of noise with wide bandwidth, from 0.1 to 1 GHz. An excellent agreement between experiment and theory with no fitting parameter is obtained. In particular, we find that the current noise of the junction of resistance R when one electrode is at temperature T and the other one at zero temperature is given by S = 2 ln2 kB T /R.

cond-mat.mes-hall↗

arXiv2020

Fundamental and Environmental Contributions to the Cyclostationary Third Moment of Current Fluctuations in a Tunnel Junction

Current fluctuations generated by tunnel junctions are known to be non-Gaussian. However, this property is lost when fluctuations are measured at high frequency and limited bandwidth. We show that the quadratures of the electric field generated by a tunnel junction at frequency $f$ displays third order correlations, i.e. skewness, when the junction is electrically driven at $3f$, revealing the Poisonnian statistic of charge transfer by the barrier even at short time-scales. In addition to this intrinsic contribution from the junction, we observe extra correlations induced by the environmental noise at frequency $f$ as well as a feedback effects coming from the environmental impedance not only at frequency $f$ but also at some multiples of $f$.

cond-mat.mes-hall↗

arXiv2019

Unidimensional Time Domain Quantum Optics

Choosing the right first quantization basis in quantum optics is critical for the interpretation of experimental results. The usual frequency basis is, for instance, inappropriate for short, subcycle waveforms. Deriving first quantization in time domain shows that the electromagnetic field is not directly proportional, nor even causally related, to the photonic field (the amplitude probability of a photon detection). We derive the relation between the two and calculate the statistics of the electromagnetic field for specific states in time domain, such as the single photon Fock state. We introduce the dual of the Hamiltonian in time domain and extend the concept of quadratures to all first quantization bases.

quant-ph↗

arXiv2019

Parametric amplification and squeezing with an ac- and dc-voltage biased superconducting junction

We theoretically investigate a near-quantum-limited parametric amplifier based on the nonlinear dynamics of quasiparticles flowing through a superconducting-insulator-superconducting junction. Photon-assisted tunneling, resulting from the combination of dc- and ac-voltage bias, gives rise to a strong parametric interaction for the electromagnetic modes reflected by the junction coupled to a transmission line. We show phase-sensitive and phase-preserving amplification, together with single- and two-mode squeezing. For an aluminum junction pumped at twice the center frequency, $ω_0/2π=6$~GHz, we predict narrow-band phase-sensitive amplification of microwaves signals to more than 20 dB, and broadband phase-preserving amplification of 20 dB over a 1.2 GHz 3-dB bandwidth. We also predict single- and two-mode squeezing reaching more than -12 dB over 5.3 GHz 3-dB bandwidth. Moreover, with a simple impedance matching circuit, we demonstrate 3 dB bandwidth reaching 4.3 GHz for 20 dB of gain. A key feature of the device is that its performance can be controlled in-situ with the applied dc- and ac-voltage biases.

cond-mat.mes-hall↗

arXiv2018

Statistics of the quantized microwave electromagnetic field in mesoscopic elements at low temperature

The quantum behaviour of the electromagnetic field in mesoscopic elements is intimately linked to the quantization of the charge. In order to probe nonclassical aspects of the field in those elements, it is essential that thermal noise be reduced to the quantum level, i.e. to scales where kT < hν. This is easily achieved in dilution refrigerators for frequencies of a few GHz, i.e. in the microwave domain. Several recent experiments have highlighted the link between discrete charge transport and discrete photon emission in simple mesoscopic elements such as a tunnel junction. Photocount statistics are inferred from the measurement of continuous variables such as the quadratures of the field.

quant-ph↗

arXiv2018

Photon-assisted Dynamical Coulomb Blockade in a Tunnel Junction

We report measurements of photon-assisted transport and noise in a tunnel junction in the regime of dynamical Coulomb blockade. We have measured both dc non-linear transport and low frequency noise in the presence of an ac excitation at frequencies up to 33 GHz. In both experiments we observe replicas at finite voltage of the zero bias features, a phenomenon characteristic of photon emission/absorption. However, the ac voltage necessary to explain our data is notably different for transport and noise, indicating that usual theory of photon-assisted phenomena fails to account for our observations.

cond-mat.mes-hall↗

arXiv2018

Non-Gaussian Current Fluctuations in a Short Diffusive Conductor

We report the measurement of the third moment of current fluctuations in a short metallic wire at low temperature. The data are deduced from the statistics of voltage fluctuations across the conductor using a careful determination of environmental contributions. Our results at low bias agree very well with theoretical predictions for coherent transport with no fitting parameter. By increasing the bias voltage we explore the cross-over from elastic to inelastic transport.

cond-mat.mes-hall↗

arXiv2016

Characterization and control of charge transfer in a tunnel junction

Charge transfer in a tunnel junction is studied under dc and ac voltage bias using quantum shot noise. Under dc voltage bias $V$, spectral density of noise measured within a very large bandwidth enables to deduce the current-current correlator in the time domain by Fourier transform. This correlator exhibits regular oscillations proving that electrons try to cross the junction regularly, every $h/eV$. Using harmonic and bi-harmonic ac voltage bias, we then show that quasiparticles excitations can be transferred through the junction in a controlled way. By measuring the reduction of the excess shot noise, we are able to determine the number of electron-hole pairs surrounding the injected electrons and demonstrate that bi-harmonic voltage pulses realize an on-demand electron source with a very small admixture of electron-hole pairs.

cond-mat.mes-hall↗

arXiv2016

Non-Classical Radiation Emission By A Coherent Conductor

We report experimental evidence that the microwave electromagnetic field generated by a normal conductor, here a tunnel junction placed at ultra-low temperature, can be non-classical. By measuring the quadratures of the electromagnetic field at one or two frequencies in the GHz range, we demonstrate the existence of squeezing as well as entanglement in such radiation. In one experiment, we observe that the variance of one quadrature of the photo-assisted noise generated by the junction goes below its vacuum level. In the second experiment, we demonstrate the existence of correlations between the quadratures taken at two frequencies, which can be stronger than allowed by classical mechanics, proving that the radiation at those two frequencies are entangled.

cond-mat.mes-hall↗

arXiv2016

Direct measurement of the electron energy relaxation dynamics in metallic wires

We present measurements of the dynamical response of thermal noise to an ac excitation in conductors at low temperature. From the frequency dependence of this response function - the noise thermal impedance - in the range 1 kHz-1 GHz we obtain direct determinations of the inelastic relaxation times relevant in metallic wires at low temperature: the electron-phonon scattering time and the diffusion time of electrons along the wires. Combining these results with that of resistivity provides a measurement of heat capacity of samples made of thin film. The simplicity and reliability of this technique makes it very promising for future applications in other systems.

cond-mat.mes-hall↗

arXiv2016

Photon pair shot noise in electron shot noise

There exists a fascinating dual representation of the electric ac current flowing through a normal conductor. On the one hand, it can be understood in terms of charge transport. On the other hand, it consists in an electomagnetic field guided by conducting structures embedded in an insulator. The former point of view, in its quantum version, is particularly adapted to describe the electron shot noise in a coherent conductor, like a tunnel junction at ultra-low temperature. However, when the junction is appropriately biased by a dc and an ac voltage, the noise it generates is best analyzed using the latter representation and the tools of quantum optics, as the radiation exhibits clear signs of non-classicality. Herein, we report the measurement of the statistics of photons emitted by such a tunnel junction. We observe a photon shot noise characteristic of photon pair emission, as its Fano factor for small signal is above unity. The theory of electron shot noise, dealing exclusively with the tunneling of charges through the junction, quantitatively fits the data from which photon shot noise is extracted. This experiment thus provides a clear link between the dual representations.

cond-mat.mes-hall↗

arXiv2016

Electron and electron-hole quasiparticle states in a driven quantum contact

We study the many-body electronic state created by a time-dependent drive of a mesoscopic contact. The many-body state is expressed manifestly in terms of single-electron and electron-hole quasiparticle excitations with the amplitudes and probabilities of creation which depend on the details of the applied voltage. We experimentally probe the time dependence of the constituent electronic states by using an analog of the optical Hong-Ou-Mandel correlation experiment where electrons emitted from the terminals with a relative time delay collide at the contact. The electron wave packet overlap is directly related to the current noise power in the contact. We have confirmed the time dependence of the electronic states predicted theoretically by measurements of the current noise power in a tunnel junction under harmonic excitation.

cond-mat.mes-hall↗

arXiv2015

Discrete photon statistics from continuous microwave measurements

Photocount statistics are an important tool for the characterization of electromagnetic fields, especially for fields with an irrelevant phase. In the microwave domain, continuous rather than discrete measurements are the norm. Using a novel approach, we recover discrete photon statistics from the cumulants of a continuous distribution of field quadrature measurements. The use of cumulants allows the separation between the signal of interest and experimental noise. Using a parametric amplifier as the first stage of the amplification chain, we extract useful data from up to the sixth cumulant of the continuous distribution of a coherent field, hence recovering up to the third moment of the discrete statistics associated with a signal with much less than one average photon.

quant-ph↗

arXiv2015

Quantum optics theory of electronic noise in coherent conductors

We consider the electromagnetic field generated by a coherent conductor in which electron transport is described quantum mechanically. We obtain an input-output relation linking the quantum current in the conductor to the measured electromagnetic field. This allows us to compute the outcome of measurements on the field in terms of the statistical properties of the current. We moreover show how under ac-bias the conductor acts as a tunable medium for the field, allowing for the generation of single- and two-mode squeezing through fermionic reservoir engineering. These results explain the recently observed squeezing using normal tunnel junctions [G. Gasse et al., Phys. Rev. Lett. 111 136601 (2013); J.-C. Forgues et al., Phys. Rev. Lett. 114 130403 (2015)].

cond-mat.mes-hall↗