Coherent frequency conversion in a superconducting artificial atom with two internal degrees of freedom.

By adding a large inductance in a dc-SQUID phase qubit loop, one decouples the junctions' dynamics and creates a superconducting artificial atom with two internal degrees of freedom. In addition to the usual symmetric plasma mode (s mode) which gives rise to the phase qubit, an antisymmetric mode (a mode) appears. These two modes can be described by two anharmonic oscillators with eigenstates |ns> and |na> for the s and a mode, respectively. We show that a strong nonlinear coupling between the modes leads to a large energy splitting between states |0s,1a> and |2s,0a>. Finally, coherent frequency conversion is observed via free oscillations between the states |0s,1a> and |2s,0a>.

Nonlinear coupling between the two oscillation modes of a dc SQUID.

We make a detailed theoretical description of the two-dimensional nature of a dc SQUID, analyzing the coupling between its two orthogonal phase oscillation modes. While it has been shown that the mode defined as "longitudinal" can be initialized, manipulated, and measured, so as to encode a quantum bit of information, the mode defined as "transverse" is usually repelled at high frequency and does not interfere in the dynamics. We show that, using typical parameters of existing devices, the transverse mode energy can be made of the order of the longitudinal one. In this regime, we can observe a strong coupling between these modes, described by a Hamiltonian providing a wide range of interesting effects, such as conditional quantum operations and entanglement. This coupling also creates an atomiclike structure for the combined two mode states, with a V-like scheme.

Quantum dynamics in a camelback potential of a dc SQUID.

We investigate a quadratic-quartic anharmonic oscillator formed by a potential well between two potential barriers. We realize this novel potential with a dc SQUID at near-zero current bias and flux bias near half a flux quantum. Escape out of the central well can occur via tunneling through either of the two barriers. We find good agreement with a generalized double-path macroscopic quantum tunneling theory. We also demonstrate an "optimal line" in current and flux bias along which the oscillator, which can be operated as a phase qubit, is insensitive to decoherence due to low-frequency current fluctuations.

Strong tunable coupling between a superconducting charge and phase qubit.

We have realized a tunable coupling over a large frequency range between an asymmetric Cooper pair transistor (charge qubit) and a dc SQUID (phase qubit). Our circuit enables the independent manipulation of the quantum states of each qubit as well as their entanglement. The measurement of the charge qubit's quantum states is performed by an adiabatic quantum transfer from the charge to the phase qubit. The measured coupling strength is in agreement with an analytic theory including a capacitive and a tunable Josephson coupling between the two qubits.

[Clitoris and G spot: an intimate affair]. / Clitoris et point G: liaison fatale.

Ultrasonography is a good means for studying the clitoris and its relationship with the G spot. We used it to demonstrate that clitoral bodies have a descending movement and come close to the distal anterior vaginal wall during a voluntary or reflex contraction of levator ani muscles. This fact could explain the particular sensitivity of the G spot and its role in the orgasm.

Coherent oscillations in a superconducting multilevel quantum system.

We have observed coherent oscillations in a multilevel quantum system, formed by a current-biased dc SQUID. These oscillations have been induced by applying resonant microwave pulses of flux. Quantum measurement is performed by a nanosecond flux pulse that projects the final state onto one of two different voltage states of the dc SQUID, which can be read out. The number of quantum states involved in the coherent oscillations increases with increasing microwave power. The dependence of the oscillation frequency on microwave power deviates strongly from the linear regime expected for a two-level system and can be very well explained by a theoretical model taking into account the anharmonicity of the multilevel system.

Evidence of two-dimensional macroscopic quantum tunneling of a current-biased dc SQUID.

The escape probability out of the superconducting state of a hysteretic dc SQUID has been measured at different values of the applied magnetic flux. At low temperatures, the escape current and the width of the probability distribution are temperature independent but they depend on flux. Experimental results do not fit the usual one-dimensional macroscopic quantum tunneling (MQT) law but are perfectly accounted for by the two-dimensional MQT behavior as we propose here. Near zero flux, our data confirms the recent MQT observation in a dc SQUID [Phys. Rev. Lett. 89, 98301 (2002)]].

One-shot quantum measurement using a hysteretic dc SQUID.

We propose a single shot quantum measurement to determine the state of a Josephson charge quantum bit (qubit). The qubit is a Cooper pair box and the measuring device is a two junction superconducting quantum interference device (dc SQUID). This coupled system exhibits a close analogy with a Rydberg atom in a high Q cavity, except that in the present device we benefit from the additional feature of escape from the supercurrent state by macroscopic quantum tunneling, which provides the final readout. We test the feasibility of our idea against realistic experimental circuit parameters and by analyzing the phase fluctuations of the qubit.

[Update on prenatal diagnosis of osteogenesis imperfecta type II : an index case report diagnosed by ultrasonography in the first trimester]. / Mise au point sur le diagnostic précoce d'ostéogenèse de type II: à propos d'un cas index diagnostiqué par échographie au premier trimestre de la grossesse.

INTRODUCTION: A case of osteogenesis imperfecta type II diagnosed in the first trimester of pregnancy. DISCUSSION: Lethal osteogenesis imperfecta is a disorder characterized by collagen abnormalities resulting in dwarfism, bone fragility and deformity leading to death in utero or in the perinatal period. Molecular and biochemical studies demonstrate that OI type II results from mutations in either COL1 A1 or COL1 A2 which encode for the chains of type I procollagen. Early diagnosis by US examination in first trimester relies on shortening and bowing of long bones, multiple fractures and hypoechogenicity of the skeleton. When ultrasound examination suspects OI type II, the diagnosis can be accomplished in the first trimester by biochemical analysis if the collagen defect is characterized. CONCLUSION: OI type II results mainly from private mutations and parental mosaicism is an important cause of recurrence making genetic counselling difficult.

Modulación de la respuesta inmunitaria por la proteína p-24 HIV-1: evidencias de un efecto diferencial sobre la respuesta alogénica in vitro / Modulation of immune response by HIV-1 p24 protein: evidence for a differential effect in allogeneic response in vitro

Es conocido que el virus de la inmunodeficiencia humana (VIH), el agente etiológico del sîndrome de la inmunodeficiencia adquirida humana (SIDA), induce un profundo desajuste de la respuesta inmunitaria, incluso en las etapas tempranas de la infección cuando los individuos son asintomáticos y clínicamente estables. La suceptibilidad y la progresión de la infección pueden ser explicadas por diferencias entre las distintas especies de VIH; sin embargo, varios estudios han descrito una asociación entre la expresión del TCR-V y el complejo mayor de histocompatibilidad (HLA) en los pacientes infectados por el VIH. También ha sido reportado que la respuesta inmunitaria aloespecífica juega un papel importante durante la fase aguda de la infección pudiendo inducir protección contra la infección, probablemente por la elimination de las células infectadas en etapas tempranas.Nosotros estudiamos el papel de la proteína recombinante p-24 HIV-1 durante la inducción de una respuesta alogénica in vitro y observamos que la p-24 HIV-1 es capaz de inducir tanto un aumento de la respuesta alogénica como también una disminución de la misma. Las moléculas HLA (clase I) podrían estar jugando un papel importante en los resultados obtenidos, ya sea incrementando o disminuyendo la respuesta alogénica. Por lo tanto, durante la aloestimulación, la proteína p-24 HIV-1 pudiera estar desempeñando un papel en la transmisión de la infección por el VIH aumentando las células blanco del virus (AU)

Sonographic diagnosis of spina bifida at 12 weeks: heading towards indirect signs.

Retrospective examination of ultrasound images obtained at 12 weeks of gestation in two fetuses with spina bifida demonstrated retraction of the frontal bones, resulting in an acorn-shaped head, the cerebral peduncles appearing parallel to each other. These craniocerebral signs may improve the accuracy of first-trimester diagnosis of spina bifida by sonography.

Coherent low-energy charge transport in a diffusive S-N-S junction.

We have studied the current-voltage characteristics of diffusive mesoscopic Nb-Cu-Nb Josephson junctions with highly transparent Nb-Cu interfaces. We consider the low-voltage and high-temperature regime eV < epsilon(c) < k(B)T, where epsilon(c) is the Thouless energy. The observed excess current as well as the observed subharmonic Shapiro steps under microwave irradiation suggest the occurrence of low-energy coherent multiple Andreev reflection.

Experimental evidence of one-dimensional plasma modes in superconducting thin wires.

We have studied niobium superconducting thin wires deposited onto a SrTiO3 substrate. By measuring the reflection coefficient of the wires, resonances are observed in the superconducting state in the 130 MHz to 4 GHz range. They are interpreted as standing wave resonances of one-dimensional plasma modes propagating along the superconducting wire. The experimental dispersion law, omega versus q, presents a linear dependence over the entire wave vector range. The modes are softened as the temperature increases close the superconducting transition temperature. Very good agreement is obtained between our data and the predicted dispersion relation of one-dimensional plasma modes.