Quasiparticle Dynamics in a Superconducting Qubit Irradiated by a Localized Infrared Source.

A known source of decoherence in superconducting qubits is the presence of broken Cooper pairs, or quasiparticles. These can be generated by high-energy radiation, either present in the environment or purposefully introduced, as in the case of some hybrid quantum devices. Here, we systematically study the properties of a transmon qubit under illumination by focused infrared radiation with various powers, durations, and spatial locations.

Engineering superconducting qubits to reduce quasiparticles and charge noise.

Identifying, quantifying, and suppressing decoherence mechanisms in qubits are important steps towards the goal of engineering a quantum computer or simulator. Superconducting circuits offer flexibility in qubit design; however, their performance is adversely affected by quasiparticles (broken Cooper pairs). Developing a quasiparticle mitigation strategy compatible with scalable, high-coherence devices is therefore highly desirable.

Reducing the impact of radioactivity on quantum circuits in a deep-underground facility.

As quantum coherence times of superconducting circuits have increased from nanoseconds to hundreds of microseconds, they are currently one of the leading platforms for quantum information processing. However, coherence needs to further improve by orders of magnitude to reduce the prohibitive hardware overhead of current error correction schemes. Reaching this goal hinges on reducing the density of broken Cooper pairs, so-called quasiparticles.

Photon-Assisted Charge-Parity Jumps in a Superconducting Qubit.

We evaluate the rates of energy and phase relaxation of a superconducting qubit caused by stray photons with energy exceeding the threshold for breaking a Cooper pair. All channels of relaxation within this mechanism are associated with the change in the charge parity of the qubit, enabling the separation of the photon-assisted processes from other contributions to the relaxation rates. Among the signatures of the new mechanism is the same order of rates of the transitions in which a qubit loses or gains energy, which is in agreement with recent experiments.

Loss Mechanisms and Quasiparticle Dynamics in Superconducting Microwave Resonators Made of Thin-Film Granular Aluminum.

Superconducting high kinetic inductance elements constitute a valuable resource for quantum circuit design and millimeter-wave detection. Granular aluminum (grAl) in the superconducting regime is a particularly interesting material since it has already shown a kinetic inductance in the range of nH/□ and its deposition is compatible with conventional Al/AlOx/Al Josephson junction fabrication. We characterize microwave resonators fabricated from grAl with a room temperature resistivity of 4×10^{3}  μΩ cm, which is a factor of 3 below the superconductor to insulator transition, showing a kinetic inductance fraction close to unity.

Synthesis and conformational analysis of a simplified inositol-model of the Streptococcus pneumoniae 19F capsular polysaccharide repeating unit.

Carbohydrate mimics have been studied for a long time as useful sugar substitutes, both in the investigation of biological events and in the treatment of sugar-related diseases. Here we report further evaluation of the capabilities of inositols as carbohydrate substitutes. The conformational features of an inositol-model of a simplified repeating unit corresponding to the capsular polysaccharide of Streptococcus pneumoniae 19F has been evaluated by computational analysis, and compared to the native repeating unit.

Useful access to enantiomerically pure protected inositols from carbohydrates: the aldohexos-5-uloses route.

The intramolecular aldol condensation of aldohexos-5-ulose derivatives of the D- and L- stereoseries has been studied. Only one of the four possible inososes was isolated from both stereoseries in reasonable yields (30-38%). The results obtained, together with the previous findings for the L- and L- stereoseries, allowed for the rationalisation of a mechanism of the reaction based on open-transition-state models and electron-withdrawing inductive effects.

Suppressing relaxation in superconducting qubits by quasiparticle pumping.

Dynamical error suppression techniques are commonly used to improve coherence in quantum systems. They reduce dephasing errors by applying control pulses designed to reverse erroneous coherent evolution driven by environmental noise. However, such methods cannot correct for irreversible processes such as energy relaxation.

Non-Poissonian quantum jumps of a fluxonium qubit due to quasiparticle excitations.

As the energy relaxation time of superconducting qubits steadily improves, nonequilibrium quasiparticle excitations above the superconducting gap emerge as an increasingly relevant limit for qubit coherence. We measure fluctuations in the number of quasiparticle excitations by continuously monitoring the spontaneous quantum jumps between the states of a fluxonium qubit, in conditions where relaxation is dominated by quasiparticle loss. Resolution on the scale of a single quasiparticle is obtained by performing quantum nondemolition projective measurements within a time interval much shorter than T₁, using a quantum-limited amplifier (Josephson parametric converter).

Measurement and control of quasiparticle dynamics in a superconducting qubit.

Superconducting circuits have attracted growing interest in recent years as a promising candidate for fault-tolerant quantum information processing. Extensive efforts have always been taken to completely shield these circuits from external magnetic fields to protect the integrity of the superconductivity. Here we show vortices can improve the performance of superconducting qubits by reducing the lifetimes of detrimental single-electron-like excitations known as quasiparticles.

Flux qubits with long coherence times for hybrid quantum circuits.

We present measurements of superconducting flux qubits embedded in a three dimensional copper cavity. The qubits are fabricated on a sapphire substrate and are measured by coupling them inductively to an on-chip superconducting resonator located in the middle of the cavity. At their flux-insensitive point, all measured qubits reach an intrinsic energy relaxation time in the 6-20  μs range and a pure dephasing time comprised between 3 and 10  μs.

Coherent suppression of electromagnetic dissipation due to superconducting quasiparticles.

Owing to the low-loss propagation of electromagnetic signals in superconductors, Josephson junctions constitute ideal building blocks for quantum memories, amplifiers, detectors and high-speed processing units, operating over a wide band of microwave frequencies. Nevertheless, although transport in superconducting wires is perfectly lossless for direct current, transport of radio-frequency signals can be dissipative in the presence of quasiparticle excitations above the superconducting gap. Moreover, the exact mechanism of this dissipation in Josephson junctions has never been fully resolved experimentally.

Antiviral activity of mycophenolic acid derivatives in plants.

antiviral agents; chemotherapy; polyamidoamine; multivalency.

Stereoselective synthesis of β-d-GlcNAc-(1→4)-D-Glc disaccharide starting from lactose.

The stereoselective preparation of the β-d-GlcNAc-(1→4)-D-Glc disaccharide starting from known 4-O-[6-O-(1-methoxy-1-methylethyl)-3,4-O-isopropylidene-β-d-talopyranosyl]-2,3:5,6-di-O-isopropylidene-aldehydo-D-glucose dimethyl acetal (2), in turn easily obtained from lactose, is reported. Key steps of this new procedure, that avoids the glycosylation reaction, are (a) a first epimerization at C-4' through an unusual procedure involving a completely stereospecific hydroboration-oxidation of the enol ether group of the hex-4-enopyranoside 4, obtained from 3 by base promoted acetone elimination, (b) an amination with inversion by S(N)2 reaction on an imidazylate intermediate, and, finally, (c) N-acetylation followed by complete deprotection.

Prevalence of oxetanose forms in the tautomeric equilibrium of β-hydroxy-1,5-dicarbonyl monosaccharides.

The synthesis of 4-deoxy- and 4-deoxy-4-C-methylhexos-5-uloses, starting from 4-deoxyhex-4-enopyranosides, and a nuclear magnetic resonance (NMR) study of their isomeric composition are reported. The NMR spectra show that the two δ-dicarbonyl sugars exist as two anomeric α- and β-oxetanosyl forms, derived from the hemiacetalization of the C-3 hydroxyl group with the aldehydic carbon. The observed tautomeric equilibria have been rationalized with computational calculations.

Quantum-fluctuation effects in the transport properties of ultrathin films of disordered superconductors above the paramagnetic limit.

We study the transport in ultrathin disordered film near the quantum critical point induced by the Zeeman field. We calculate corrections to the normal state conductivity due to quantum pairing fluctuations. The fluctuation-induced transport is mediated by virtual rather than real quasiparticle excitations.

Measurements of quasiparticle tunneling dynamics in a band-gap-engineered transmon qubit.

We have engineered the band gap profile of transmon qubits by combining oxygen-doped Al for tunnel junction electrodes and clean Al as quasiparticle traps to investigate energy relaxation due to quasiparticle tunneling. The relaxation time T1 of the qubits is shown to be insensitive to this band gap engineering. Operating at relatively low-E(J)/E(C) makes the transmon transition frequency distinctly dependent on the charge parity, allowing us to detect the quasiparticles tunneling across the qubit junction.

Observation of high coherence in Josephson junction qubits measured in a three-dimensional circuit QED architecture.

Superconducting quantum circuits based on Josephson junctions have made rapid progress in demonstrating quantum behavior and scalability. However, the future prospects ultimately depend upon the intrinsic coherence of Josephson junctions, and whether superconducting qubits can be adequately isolated from their environment. We introduce a new architecture for superconducting quantum circuits employing a three-dimensional resonator that suppresses qubit decoherence while maintaining sufficient coupling to the control signal.

Efficient double glycoconjugation to naturalize high molecular weight disperse dyes.

Commercially available Disperse Orange 29 (1a) and Disperse Red 1 (2a) were elaborated to glycoconjugated species, following a new version of a previously-described 'naturalisation' procedure. Glutamic acid was chosen to achieve a double glycoconjugation, which is essential to give to the original disperse dye a water solubility suitable for reaching optimal dyeing conditions. UV-vis plot of the 'naturalised' species showed negligible differences when compared to those of the commercial dyes.

Origin of excess low-energy states in a disordered superconductor in a Zeeman field.

Tunneling density of states measurements of disordered superconducting Al films in high Zeeman fields reveal a significant population of subgap states which cannot be explained by standard BCS theory. We provide a natural explanation of these excess states in terms of a novel disordered Larkin-Ovchinnikov phase that occurs near the spin-paramagnetic transition at the Chandrasekhar-Clogston critical field. The disordered Larkin-Ovchinnikov superconductor is characterized by a pairing amplitude that changes sign at domain walls.

Spin-resolved tunneling studies of the exchange field in EuS/Al bilayers.

We use spin-resolved electron tunneling to study the exchange field in the Al component of EuS/Al bilayers, in both the superconducting and normal-state phases of the Al. Contrary to expectation, we show that the exchange field H(ex) is a nonlinear function of applied field, even in applied fields that are well beyond the EuS coercive field. Furthermore, the magnitude H(ex) is unaffected by the superconducting phase.

Quasiparticle relaxation of superconducting qubits in the presence of flux.

Quasiparticle tunneling across a Josephson junction sets a limit for the lifetime of a superconducting qubit state. We develop a general theory of the corresponding decay rate in a qubit controlled by a magnetic flux. The flux affects quasiparticles tunneling amplitudes, thus making the decay rate flux-dependent.

Fusarium oxysporum degradation and detoxification of a new textile-glycoconjugate azo dye (GAD).

Degradation and detoxification of textile dyes are of interest due to the huge environmental impact of such chemicals. An isolate of Fusarium oxysporum was used to degrade and to detoxify a new chemical class of textile dyes called Glycoconjugate Azo Dye (GAD). After 6 d of growth in a liquid batch culture, the fungus degraded the dye and the culture medium at the end of incubation period showed a ˜100% detoxification compared to the initial dye solution.

Tunable superconducting nanoinductors.

We characterize inductors fabricated from ultra-thin, approximately 100 nm wide strips of niobium (Nb) and niobium nitride (NbN). These nanowires have a large kinetic inductance in the superconducting state. The kinetic inductance scales linearly with the nanowire length, with a typical value of 1 nH µm(-1) for NbN and 44 pH µm(-1) for Nb at a temperature of 2.