Ultrahigh finesse Fabry-Perot superconducting resonator

We have built a microwave Fabry-Perot resonator made of diamond-machined copper mirrors coated with superconducting niobium. Its damping time (Tc = 130 ms at 51 GHz and 0.8 K) corresponds to a finesse of 4.6 x 109, the highest ever reached for a Fabry-Perot in any frequency range. This result opens novel perspectives for quantum information, decoherence and non-locality studies

Adiabatic elimination for multi-partite open quantum systems with non-trivial zero-order dynamics

International audienceWe provide model reduction formulas for open quantum systems consisting of a target component which weakly interacts with a strongly dissipative environment. The time-scale separation between the uncoupled dynamics and the interaction allows to employ tools from center manifold theory and geometric singular perturbation theory to eliminate the variables associated to the environment (adiabatic elimination) with high-order accuracy. An important specificity is to preserve the quantum structure: reduced dynamics in (p ositive) Lindblad form and coordinate mappings in Kraus form. We provide formulas of the reduced dynamics. Themain contributions of this paper are (i) to show how the decomposition of the environment into $K$ components enables its efficient treatment, avoiding the quantum curse of dimension; and (ii) to extend the results to the case where the target component is subject to Hamiltonian evolution at the fast time-scale. We apply our theory to a microwave superconducting quantum resonator subject to material losses, and we show that our reduced-order model can explain the transmission spectrum observed in a recent pump probe experiment

A new method of probing mechanical losses of coatings at cryogenic temperatures

A new method of probing mechanical losses and comparing the corresponding deposition processes of metallic and dielectric coatings in 1-100 MHz frequency range and cryogenic temperatures is presented. The method is based on the use of extremely high-quality quartz acoustic cavities whose internal losses are orders of magnitude lower than any available coatings nowadays. The approach is demonstrated for Chromium, Chromium/Gold and a multilayer tantala/silica coatings. The ${\rm Ta}_2{\rm O}_5/{\rm Si}{\rm O}_2$ coating has been found to exhibit a loss angle lower than $1.6\times10^{-5}$ near 30 {\rm MHz} at 4 {\rm K}. The results are compared to the previous measurements

Quantum jumps of light recording the birth and death of a photon in a cavity

A microscopic system under continuous observation exhibits at random times sudden jumps between its states. The detection of this essential quantum feature requires a quantum non-demolition (QND) measurement repeated many times during the system evolution. Quantum jumps of trapped massive particles (electrons, ions or molecules) have been observed, which is not the case of the jumps of light quanta. Usual photodetectors absorb light and are thus unable to detect the same photon twice. They must be replaced by a transparent counter 'seeing' photons without destroying them3. Moreover, the light has to be stored over a duration much longer than the QND detection time. We have fulfilled these challenging conditions and observed photon number quantum jumps. Microwave photons are stored in a superconducting cavity for times in the second range. They are repeatedly probed by a stream of non-absorbing atoms. An atom interferometer measures the atomic dipole phase shift induced by the non-resonant cavity field, so that the final atom state reveals directly the presence of a single photon in the cavity. Sequences of hundreds of atoms highly correlated in the same state, are interrupted by sudden state-switchings. These telegraphic signals record, for the first time, the birth, life and death of individual photons. Applying a similar QND procedure to mesoscopic fields with tens of photons opens new perspectives for the exploration of the quantum to classical boundary

Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo

Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level

Ultralight vector dark matter search using data from the KAGRA O3GK run

Among the various candidates for dark matter (DM), ultralight vector DM can be probed by laser interferometric gravitational wave detectors through the measurement of oscillating length changes in the arm cavities. In this context, KAGRA has a unique feature due to differing compositions of its mirrors, enhancing the signal of vector DM in the length change in the auxiliary channels. Here we present the result of a search for U(1)B−L gauge boson DM using the KAGRA data from auxiliary length channels during the first joint observation run together with GEO600. By applying our search pipeline, which takes into account the stochastic nature of ultralight DM, upper bounds on the coupling strength between the U(1)B−L gauge boson and ordinary matter are obtained for a range of DM masses. While our constraints are less stringent than those derived from previous experiments, this study demonstrates the applicability of our method to the lower-mass vector DM search, which is made difficult in this measurement by the short observation time compared to the auto-correlation time scale of DM

Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network

Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects

Reconstruction d'états non classiques du champ en électrodynamique quantique en cavité

Our cavity Quantum Electrodynamics experiment consists of two simple and well controlled systems interacting in the strong coupling regime: two-level atoms and a single mode of the electromagnetic field. The use of superconducting mirrors allows to trap a microwave field in a cavity for times up to a tenth of a second. In order to probe and to manipulate the trapped field, we use Rubidium atoms excited in a circular Rydberg state. They cross one by one the cavity detuned with respect to their transition. The atoms thus behave as small atomic clocks whose rate is affected by the presence of photons inside the mode through the light shift effect. We measure the small modifications of the atomic superposition's phase after the atoms have crossed the cavity by means of a Ramsey interferometry technique, allowing us to count the number of trapped photons. Slightly modifying this method, one can reconstruct the full density matrix of the state. We applied this technique to several non-classical states of the field: Fock states with a well determined number of photons, and Schrödinger's cat states, which are quantum superpositions of two classical fields with different phases. By repeating the reconstruction scheme for several delays after preparation, we are able to record a step-by-step movie of the time evolution of the state. The evolution of the Schrödinger's cat state under the effect of decoherence sheds new light on the problem of quantum measurement and the quantum to classical boundary.Notre dispositif d'électrodynamique quantique en cavité permet de faire interagir dans le régime de couplage fort deux systèmes simples et parfaitement contrôlés : des atomes à deux niveaux et un seul mode du champ électromagnétique. Des miroirs supraconducteurs permettent de stocker le champ électromagnétique micro-onde dans une cavité pendant plus d'un dixième de seconde. Afin de sonder et de manipuler le champ piégé, nous utilisons des atomes de Rubidium excités dans les états de Rydberg circulaires. Les atomes interagissent un à un avec la cavité dans le régime dispersif. Ils se comportent alors comme de petites horloges dont la fréquence est affectée par les photons piégés grâce au phénomène de déplacement lumineux. Les petites modifications de la phase atomique après la traversée du mode sont mesurées par interférométrie de Ramsey, permettant de compter le nombre de photons piégés. En adaptant légèrement la méthode, on parvient à reconstruire complètement la matrice densité du champ piégé. Cette technique a été appliquée à différents états non-classiques du champ : des états de Fock, dont le nombre de photons est parfaitement déterminé, et des états chat de Schrödinger. Ces derniers sont formés de la superposition quantique de deux champs classiques de phases différentes. En répétant la procédure de reconstruction pour plusieurs délais successifs après la préparation, on obtient un film image par image de l'évolution temporelle de l'état. L'étude de l'évolution de l'état chat de Schrödinger sous l'effet de la décohérence apporte un éclairage intéressant sur le problème de la mesure en mécanique quantique et la frontière entre les mondes classique et quantique

Adiabatic elimination for multi-partite open quantum systems with non-trivial zero-order dynamics

International audienceWe provide model reduction formulas for open quantum systems consisting of a target component which weakly interacts with a strongly dissipative environment. The time-scale separation between the uncoupled dynamics and the interaction allows to employ tools from center manifold theory and geometric singular perturbation theory to eliminate the variables associated to the environment (adiabatic elimination) with high-order accuracy. An important specificity is to preserve the quantum structure: reduced dynamics in (p ositive) Lindblad form and coordinate mappings in Kraus form. We provide formulas of the reduced dynamics. Themain contributions of this paper are (i) to show how the decomposition of the environment into $K$ components enables its efficient treatment, avoiding the quantum curse of dimension; and (ii) to extend the results to the case where the target component is subject to Hamiltonian evolution at the fast time-scale. We apply our theory to a microwave superconducting quantum resonator subject to material losses, and we show that our reduced-order model can explain the transmission spectrum observed in a recent pump probe experiment