Ballistic one-dimensional holes with strong g-factor anisotropy in germanium

We report experimental evidence of ballistic hole transport in one-dimensional quantum wires gate-defined in a strained SiGe/Ge/SiGe quantum well. At zero magnetic field, we observe conductance plateaus at integer multiples of 2e2/h. At finite magnetic field, the splitting of these plateaus by Zeeman effect reveals largely anisotropic g-factors with absolute values below 1 in the quantum-well plane, and exceeding 10 out-of-plane. This g-factor anisotropy is consistent with a heavy-hole character of the propagating valence-band states, which is in line with a predominant confinement in the growth direction. Remarkably, we observe quantized ballistic conductance in device channels up to 600 nm long. These findings mark an important step toward the realization of novel devices for applications in quantum spintronics

Nongalvanic thermometry for ultracold two-dimensional electron domains

Measuring the temperature of a two-dimensional electron gas at temperatures of a few mK is a challenging issue, which standard thermometry schemes may fail to tackle. We propose and analyze a nongalvanic thermometer, based on a quantum point contact and quantum dot, which delivers virtually no power to the electron system to be measured.Comment: 5 pages, 3 figure

The Kondo Effect in the Unitary Limit

We observe a strong Kondo effect in a semiconductor quantum dot when a small magnetic field is applied. The Coulomb blockade for electron tunneling is overcome completely by the Kondo effect and the conductance reaches the unitary-limit value. We compare the experimental Kondo temperature with the theoretical predictions for the spin-1/2 Anderson impurity model. Excellent agreement is found throughout the Kondo regime. Phase coherence is preserved when a Kondo quantum dot is included in one of the arms of an Aharonov-Bohm ring structure and the phase behavior differs from previous results on a non-Kondo dot.Comment: 10 page

Le destin des manuscrits catholiques d’Isaac Papin après sa mort : convoitise et mystère autour de la dépouille intellectuelle d’un sympathisant janséniste

Isaac Papin (1657-1709), né calviniste, est passé à la postérité pour sa conversion au catholicisme. Après avoir été le fer de lance des pajonistes au sein du Refuge, il se convertit entre les mains de Bossuet, en 1690. La seconde partie de sa vie est beaucoup moins connue. Deux dossiers de la collection Port-Royal d’Utrecht permettent de lever le voile sur un aspect totalement inédit de son parcours : ses relations avec le milieu janséniste. Si les traces sont peu nombreuses, ses relations avec Pasquier Quesnel sont attestées. Après sa mort, ses manuscrits sont convoités et finalement récupérés par les jansénistes. Les textes qu’ils contiennent sont publiés par les soins de Quesnel, en 1713, sous le titre Les deux voies opposées en matière de religion

Single-electron tunneling in InP nanowires

We report on the fabrication and electrical characterization of field-effect devices based on wire-shaped InP crystals grown from Au catalyst particles by a vapor-liquid-solid process. Our InP wires are n-type doped with diameters in the 40-55 nm range and lengths of several microns. After being deposited on an oxidized Si substrate, wires are contacted individually via e-beam fabricated Ti/Al electrodes. We obtain contact resistances as low as ~10 kOhm, with minor temperature dependence. The distance between the electrodes varies between 0.2 and 2 micron. The electron density in the wires is changed with a back gate. Low-temperature transport measurements show Coulomb-blockade behavior with single-electron charging energies of ~1 meV. We also demonstrate energy quantization resulting from the confinement in the wire.Comment: 4 pages, 3 figure

A CMOS silicon spin qubit

Silicon, the main constituent of microprocessor chips, is emerging as a promising material for the realization of future quantum processors. Leveraging its well-established complementary metal-oxide-semiconductor (CMOS) technology would be a clear asset to the development of scalable quantum computing architectures and to their co-integration with classical control hardware. Here we report a silicon quantum bit (qubit) device made with an industry-standard fabrication process. The device consists of a two-gate, p-type transistor with an undoped channel. At low temperature, the first gate defines a quantum dot (QD) encoding a hole spin qubit, the second one a QD used for the qubit readout. All electrical, two-axis control of the spin qubit is achieved by applying a phase-tunable microwave modulation to the first gate. Our result opens a viable path to qubit up-scaling through a readily exploitable CMOS platform.Comment: 12 pages, 4 figure