Mapping the optimal route between two quantum states.

A central feature of quantum mechanics is that a measurement result is intrinsically probabilistic. Consequently, continuously monitoring a quantum system will randomly perturb its natural unitary evolution. The ability to control a quantum system in the presence of these fluctuations is of increasing importance in quantum information processing and finds application in fields ranging from nuclear magnetic resonance to chemical synthesis. A detailed understanding of this stochastic evolution is essential for the development of optimized control methods. Here we reconstruct the individual quantum trajectories of a superconducting circuit that evolves under the competing influences of continuous weak measurement and Rabi drive. By tracking individual trajectories that evolve between any chosen initial and final states, we can deduce the most probable path through quantum state space. These pre- and post-selected quantum trajectories also reveal the optimal detector signal in the form of a smooth, time-continuous function that connects the desired boundary conditions. Our investigation reveals the rich interplay between measurement dynamics, typically associated with wavefunction collapse, and unitary evolution of the quantum state as described by the Schrödinger equation. These results and the underlying theory, based on a principle of least action, reveal the optimal route from initial to final states, and may inform new quantum control methods for state steering and information processing.

Observing single quantum trajectories of a superconducting quantum bit.

The length of time that a quantum system can exist in a superposition state is determined by how strongly it interacts with its environment. This interaction entangles the quantum state with the inherent fluctuations of the environment. If these fluctuations are not measured, the environment can be viewed as a source of noise, causing random evolution of the quantum system from an initially pure state into a statistical mixture--a process known as decoherence. However, by accurately measuring the environment in real time, the quantum system can be maintained in a pure state and its time evolution described by a 'quantum trajectory' determined by the measurement outcome. Here we use weak measurements to monitor a microwave cavity containing a superconducting quantum bit (qubit), and track the individual quantum trajectories of the system. In this set-up, the environment is dominated by the fluctuations of a single electromagnetic mode of the cavity. Using a near-quantum-limited parametric amplifier, we selectively measure either the phase or the amplitude of the cavity field, and thereby confine trajectories to either the equator or a meridian of the Bloch sphere. We perform quantum state tomography at discrete times along the trajectory to verify that we have faithfully tracked the state of the quantum system as it diffuses on the surface of the Bloch sphere. Our results demonstrate that decoherence can be mitigated by environmental monitoring, and validate the foundation of quantum feedback approaches based on Bayesian statistics. Moreover, our experiments suggest a new means of implementing 'quantum steering'--the harnessing of action at a distance to manipulate quantum states through measurement.

Reduction of the radiative decay of atomic coherence in squeezed vacuum.

Quantum fluctuations of the electromagnetic vacuum are responsible for physical effects such as the Casimir force and the radiative decay of atoms, and set fundamental limits on the sensitivity of measurements. Entanglement between photons can produce correlations that result in a reduction of these fluctuations below the ordinary vacuum level, allowing measurements that surpass the standard quantum limit in sensitivity. The effects of such 'squeezed states' of light on matter were first considered in a prediction of the radiative decay rates of atoms in squeezed vacuum. Despite efforts to demonstrate such effects in experiments with natural atoms, a direct quantitative observation of this prediction has remained elusive. Here we report a twofold reduction of the transverse radiative decay rate of a superconducting artificial atom coupled to continuum squeezed vacuum. The artificial atom is effectively a two-level system formed by the strong interaction between a superconducting circuit and a microwave-frequency cavity. A Josephson parametric amplifier is used to generate quadrature-squeezed electromagnetic vacuum. The observed twofold reduction in the decay rate of the atom allows the transverse coherence time, T2, to exceed the ordinary vacuum decay limit, 2T1. We demonstrate that the measured radiative decay dynamics can be used to reconstruct the Wigner distribution of the itinerant squeezed state. Our results confirm a canonical prediction of quantum optics and should enable new studies of the quantum light-matter interaction.

Stabilizing Rabi oscillations in a superconducting qubit using quantum feedback.

The act of measurement bridges the quantum and classical worlds by projecting a superposition of possible states into a single (probabilistic) outcome. The timescale of this 'instantaneous' process can be stretched using weak measurements, such that it takes the form of a gradual random walk towards a final state. Remarkably, the interim measurement record is sufficient to continuously track and steer the quantum state using feedback. Here we implement quantum feedback control in a solid-state system, namely a superconducting quantum bit (qubit) coupled to a microwave cavity. A weak measurement of the qubit is implemented by probing the cavity with microwave photons, maintaining its average occupation at less than one photon. These photons are then directed to a high-bandwidth, quantum-noise-limited amplifier, which allows real-time monitoring of the state of the cavity (and, hence, that of the qubit) with high fidelity. We demonstrate quantum feedback control by inhibiting the decay of Rabi oscillations, allowing them to persist indefinitely. Such an ability permits the active suppression of decoherence and enables a method of quantum error correction based on weak continuous measurements. Other applications include quantum state stabilization, entanglement generation using measurement, state purification and adaptive measurements.

Molecular frame photoemission by a comb of elliptical high-order harmonics: a sensitive probe of both photodynamics and harmonic complete polarization state.

Due to the intimate anisotropic interaction between an XUV light field and a molecule resulting in photoionization (PI), molecular frame photoelectron angular distributions (MFPADs) are most sensitive probes of both electronic/nuclear dynamics and the polarization state of the ionizing light field. Consequently, they encode the complex dipole matrix elements describing the dynamics of the PI transition, as well as the three normalized Stokes parameters s1, s2, s3 characterizing the complete polarization state of the light, operating as molecular polarimetry. The remarkable development of advanced light sources delivering attosecond XUV pulses opens the perspective to visualize the primary steps of photochemical dynamics in time-resolved studies, at the natural attosecond to few femtosecond time-scales of electron dynamics and fast nuclear motion. It is thus timely to investigate the feasibility of measurement of MFPADs when PI is induced e.g., by an attosecond pulse train (APT) corresponding to a comb of discrete high-order harmonics. In the work presented here, we report MFPAD studies based on coincident electron-ion 3D momentum imaging in the context of ultrafast molecular dynamics investigated at the PLFA facility (CEA-SLIC), with two perspectives: (i) using APTs generated in atoms/molecules as a source for MFPAD-resolved PI studies, and (ii) taking advantage of molecular polarimetry to perform a complete polarization analysis of the harmonic emission of molecules, a major challenge of high harmonic spectroscopy. Recent results illustrating both aspects are reported for APTs generated in unaligned SF6 molecules by an elliptically polarized infrared driving field. The observed fingerprints of the elliptically polarized harmonics include the first direct determination of the complete s1, s2, s3 Stokes vector, equivalent to (ψ, ε, P), the orientation and the signed ellipticity of the polarization ellipse, and the degree of polarization P. They are compared to so far incomplete results of XUV optical polarimetry. We finally discuss the comparison between the outcomes of photoionization and high harmonic spectroscopy for the description of molecular photodynamics.

Prediction and retrodiction for a continuously monitored superconducting qubit.

The quantum state of a superconducting transmon qubit inside a three-dimensional cavity is monitored by transmission of a microwave field through the cavity. The information inferred from the measurement record is incorporated in a density matrix ρ_{t}, which is conditioned on probe results until t, and in an auxiliary matrix E_{t}, which is conditioned on probe results obtained after t. Here, we obtain these matrices from experimental data and we illustrate their application to predict and retrodict the outcome of weak and strong qubit measurements.

Role of rotational wave packets in strong field experiments.

Complex revival features of rotational wave packets are obtained from the interplay of a molecular rotational distribution and a measured physical observable. The analysis of the measured temporal behavior can be used to retrieve either one or both quantities. We show here the first observation of high order fractional revival (up to 1/12 in CO2) using time-of-flight measurements of ion yields leading to the information required for full reconstruction of the rotational wave packet. We further show via an analysis of higher order fractional revivals in high harmonic generation that new information on the participating ionic channels can be clearly identified, showing the general implication of our results.

Spatio-temporal characterization of mid-infrared laser pulses with spatially encoded spectral shearing interferometry.

We report on the spatially resolved full amplitude and phase characterization of mid-infrared high intensity laser pulses generated in a three stage OPA. We use a spatially-encoded arrangement (SEA-)SPIDER with spectral filters for ancilla generation for spatially resolved characterization. Using five interchangeable filter sets we are able to characterize pulses from 1 to 2 µm with one single device with minimal adjustments.

Cavity-assisted quantum bath engineering.

We demonstrate quantum bath engineering for a superconducting artificial atom coupled to a microwave cavity. By tailoring the spectrum of microwave photon shot noise in the cavity, we create a dissipative environment that autonomously relaxes the atom to an arbitrarily specified coherent superposition of the ground and excited states. In the presence of background thermal excitations, this mechanism increases state purity and effectively cools the dressed atom state to a low temperature.

Measurement-induced qubit state mixing in circuit QED from up-converted dephasing noise.

We observe measurement-induced qubit state mixing in a transmon qubit dispersively coupled to a planar readout cavity. Our results indicate that dephasing noise at the qubit-readout detuning frequency is up-converted by readout photons to cause spurious qubit state transitions, thus limiting the nondemolition character of the readout. Furthermore, we use the qubit transition rate as a tool to extract an equivalent flux noise spectral density at f~1 GHz and find agreement with values extrapolated from a 1/f(α) fit to the measured flux noise spectral density below 1 Hz.

PyMoDAQ: An open-source Python-based software for modular data acquisition.

Thanks to the recent multiplication of scientific Python packages in the open-source software landscape, Data Acquisition frameworks (DAQ-Fs) appear as versatile replacements of custom-made or costly commercial solutions. PyMoDAQ is a DAQ-F focusing on easy-to-use graphical user interfaces allowing a simple control and automation of a large variety of experimental setups. Its development included a highly modular structure allowing any experimental data acquisition as a function of multiple varying parameters. It offers numerous additional functionalities: instrument and setup configuration, plotting, saving, logging, etc. Live visual feedback is available at all times to monitor the ongoing experiment. Flexibility of its user interfaces is the key advantage of PyMoDAQ allowing also its integration as the core of more focused applications. Its hierarchical binary format data saving mechanism includes experimental metadata highly compatible with FAIR (Findable, Accessible,Interoperable, Reusable) data. Among the presented characteristics, seven criteria have been chosen to judge the pertinence of PyMoDAQ as a versatile DAQ-F. They are also the basis for a comparison with other existing frameworks highlighting the novelty of PyMoDAQ.

Change in cholesterol awareness and action. Results from national physician and public surveys.

The National Heart, Lung, and Blood Institute, Bethesda, Md, sponsored national telephone surveys of practicing physicians and the adult public in 1983, 1986, and 1990 to assess attitudes and practices regarding high serum cholesterol levels. Each time, approximately 1600 physicians and 4000 adults were interviewed. Trends show continuing change in medical practice and public health behavior relating to serum cholesterol. In 1990, physicians reported treating serum cholesterol at considerably lower levels than in 1986 and 1983. The median range of serum cholesterol at which diet therapy was initiated was 5.17 to 5.66 mmol/L (200 to 219 mg/dL) in 1990, down from 6.21 to 6.70 mmol/L (240 to 259 mg/dL) in 1986 and 6.72 to 7.21 mmol/L (260 to 279 mg/dL) in 1983. The median ranges for initiating drug therapy were 6.21 to 6.70 mmol/L (240 to 259 mg/dL) in 1990, 7.76 to 8.25 mmol/L (300 to 319 mg/dL) in 1986, and 8.79 to 9.28 mmol/L (340 to 359 mg/dL) in 1983. The number of adults who reported having had their cholesterol level checked rose from 35% to 46% to 65% in 1983, 1986, and 1990, respectively. Between 1983 and 1990, the number of adults reporting a physician diagnosis of high serum cholesterol increased from 7% to 16%; the number reporting a prescribed cholesterol-lowering diet increased from 3% to 9%. Reports of self-initiated diet efforts reached a high of 19% in 1986 and decreased to 15% in 1990 compared with 1% in earlier years. In 1990, over 90% of physicians reported awareness and use of the recommendations from the Report of the National Cholesterol Education Program Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults, and the public reported marked increases in awareness of dietary methods to lower serum cholesterol. These changes suggest educational gains; the data also suggest areas for continued cholesterol educational initiatives.

A zero dead-time multi-particle time and position sensitive detector based on correlation between brightness and amplitude.

A new multi-particle time and position sensitive detector using only a set of microchannel plates, a waveform digitizer, a phosphor screen, and a CMOS camera is described. The assignment of the timing information, as taken from the microchannel plates by fast digitizing, to the positions, as recorded by the camera, is based on the COrrelation between the BRightness of the phosphor screen spots, defined as their integrated intensity and the Amplitude of the electrical signals (COBRA). Tests performed by observing the dissociation of HeH, the fragmentation of H3 into two or three fragments, and the photo-double-ionization of Xenon atoms are presented, which illustrate the performances of the COBRA detection scheme.

Flexible attosecond beamline for high harmonic spectroscopy and XUV/near-IR pump probe experiments requiring long acquisition times.

We describe the versatile features of the attosecond beamline recently installed at CEA-Saclay on the PLFA kHz laser. It combines a fine and very complete set of diagnostics enabling high harmonic spectroscopy (HHS) through the advanced characterization of the amplitude, phase, and polarization of the harmonic emission. It also allows a variety of photo-ionization experiments using magnetic bottle and COLTRIMS (COLd Target Recoil Ion Momentum Microscopy) electron spectrometers that may be used simultaneously, thanks to a two-foci configuration. Using both passive and active stabilization, special care was paid to the long term stability of the system to allow, using both experimental approaches, time resolved studies with attosecond precision, typically over several hours of acquisition times. As an illustration, applications to multi-orbital HHS and electron-ion coincidence time resolved spectroscopy are presented.

[L-Ala3]DPDPE: a new enkephalin analog with a unique opioid receptor activity profile. Further evidence of delta-opioid receptor multiplicity.

To investigate delta-opioid receptor topography near the 3-position of [D-Pen2,D-Pen5]enkephalin (DPDPE), a series of small-group 3-position analogs of DPDPE have been synthesized and assayed for binding potencies and in vitro biological activities. L-Amino acid substitutions at this position are highly favored over D-amino acid substitutions, with the smallest, [L-Ala3]DPDPE (DPADPE), being the most favored in the series investigated. [L-Ala3]DPDPE is nearly as delta-potent and more delta-selective in both rat brain binding (18 nM vs [3H] [p-ClPhe4]DPDPE and mu/delta = 610) and peripheral bioassays (12 nM in the MVD and GPI/MVD = 4500) when compared to DPDPE (8.5 nM, mu/delta = 73 and 4.1 nM, GPI/MVD = 1800, respectively). Whereas DPDPE is a potent analgesic when given icv, [L-Ala3]DPDPE is only a weak analgesic. However, [L-Ala3]DPDPE has been found to antagonize DPDPE, but not Deltorphin II, in a moderately potent (pA2 = 5.7) and selective fashion in vivo. Thus, [L-Ala3]DPDPE is a fairly potent agonist at peripheral delta receptors and is a moderately potent (mixed) antagonist of delta 1 receptors in the brain. It appears that [L-Ala3]DPDPE does not interact in any significant manner with delta 2 or mu receptors in the brain.

[125I]SNF 8702: a selective radioligand for CCKB receptors.

The CCK-8 analogue, SNF 8702, was radioiodinated. [125I]SNF 8702 showed high-affinity specific binding for both guinea pig and mouse brain tissues, whereas no specific binding was seen for guinea pig pancreatic tissue. The properties of the site labeled by [125I]SNF 8702 were characterized by binding inhibition studies for a series of CCKA and CCKB receptor ligands. The binding selectivity profile corresponded to that for the CCKB receptor. The labeled compound is stable for more than 6 weeks during storage at -20 degrees C.

Unexpected antinociceptive potency of cyclic [D-Tca1]CTAP: potential for a novel mechanism of action.

This study tested the hypothesis that compounds which may bind simultaneously to delta and mu receptors may be more potent antinociceptive agents than would be predicted from their binding affinities at individual mu and delta opioid receptors. D-Tca-Cys-Tyr-D-Trp-Arg-Thr-Pen-Thr-NH2 ([D-Tca1]CTAP) (where D-Tca is a cyclic D-tryptophan analogue) was synthesized and evaluated in radioligand competition assays, opioid bioassays, and in an antinociceptive assay (the tail-flick test in mice). Additionally, the metabolic stability of [D-Tca1]CTAP was evaluated in striatal and cerebellar tissue slices. In rat brain in vitro, [D-Tca1]CTAP competed weakly for sites labelled by [3H]D-Phe-Cys-Tyr-D-Trp-Om-Thr-Pen-Thr-NH2 ([3H]CTOP) (mu-ligand), and [3H][D-Pen2,pCl-Phe4,D-Pen5]enkephalin (delta-ligand); [D-Pen2,D-Pen5]enkephalin (DPDPE) (delta-agonist) was 6.5-fold less and 230-fold more potent, respectively, against these ligands. Additionally, in mouse isolated vas deferens and guinea pig isolated ileum smooth muscle preparations, [D-Tca1]CTAP proved to be weak as either a delta (IC50 of approximately 2 microM) or mu (IC50 > 8 microM) receptor agonist. Surprisingly, however, i.c.v. [D-Tca1]CTAP produced antinociception with potency similar to DPDPE. The antinociceptive actions of [D-Tca1]CTAP were apparently not due to a metabolite or the release of endogenous opioids, as this compound proved stable in both striatal and cerebellar tissue slices and its antinociceptive actions were not enhanced by the 'enkephalinase' inhibitor thiorphan. The suggestion that [D-Tca1]CTAP might be acting by binding simultaneously to mu and delta receptors to produce its antinociceptive effect is supported by the demonstrated antagonism resulting from mu receptor blockade with either beta-funaltrexamine (beta-FNA) or naloxonazine, or by delta receptor blockade by ICI 174,864 ([N,N-diallyl-Tyr1,Aib2,3,Leu5] enkephalin). Furthermore, the antinociceptive properties of [D-Tca1]CTAP were antagonized by (naltrindole-5'-isothiocyanate) (5'-NTII), an antagonist at the delta 2 opioid receptor subtype, but not by the delta 1 antagonist [D-Ala2,D-Leu5,Cys6]enkephalin (DALCE). Additionally, no antagonism was produced by nor-binaltorphimine (nor-BNI), a kappa antagonist. From these data, [D-Tca1]CTAP appears to bind to mu, and 5'-NTII-sensitive delta 2, opioid receptors, and may represent the first of a class of compounds which may act at an opioid receptor complex via 'self-potentiation'.

Synthesis of [D-Ala2,4'-125I-Phe3,Glu4]deltorphin and characterization of its delta opioid receptor binding properties.

Both [D-Ala2,Glu4]Deltorphin and [D-Ala2,4'-I-Phe3,Glu4]Deltorphin are highly selective ligands for delta, relative to mu, opioid receptors. Radiolabeled [D-Ala2, 4'-125I-Phe3,Glu4]Deltorphin ([125I]Deltorphin) was prepared with a specific activity of 2200 Ci/mmol from [D-Ala2, 4'-NH2-Phe3, Glu4]Deltorphin through a diazonium salt intermediate. The inhibition of [125I]Deltorphin binding to rat brain membranes by ligands selective for mu, delta, and kappa opioid receptors is consistent with binding by the radioligand to a single site having the properties of a delta opioid receptor. The results of these studies are in good agreement with those obtained by structurally different delta opioid receptor ligands. The similarity between the delta receptor site labeled by [125I]Deltorphin and those labeled by other delta receptor agonists, in contrast to differences seen by in vivo studies of their analgesic effects, is discussed.

[125I-Tyr1]biphalin binding to opioid receptors of rat brain and NG108-15 cell membranes.

Mono iodinated analogues of biphalin [(Tyr-D-Ala-Gly-Phe-NH-)2], both nonradioactive [I-Tyr1]biphalin and radioactive [125I-Tyr1]biphalin have been synthesized. The radioligand binding profiles of these compounds for two types of tissues, rat brain membranes, and NG108-15 cell membranes were identical to the parent biphalin. This is additional evidence for the hypothesis that biphalin behaves like a monomeric ligand and that only one intact tyrosine is necessary for high biological activity. The second tyrosine could be used for successful radioiodination which may greatly simplify biochemical and pharmacological studies of biphalin. The results of receptor binding studies show that the binding of both biphalin and [I-Tyr1]biphalin to the delta and mu opioid receptors are not independent. [125I-Tyr1]Biphalin binds to delta receptors as shown in NG108-15 cell membranes. Nevertheless, [125I]biphalin binding to delta receptors in rat brain membranes was hardly evident and mu receptor binding predominated or at least was much more readily detectable in this preparation.