Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 23
Filtrar
Más filtros










Base de datos
Intervalo de año de publicación
1.
Nat Commun ; 10(1): 2776, 2019 Jul 03.
Artículo en Inglés | MEDLINE | ID: mdl-31270319

RESUMEN

Silicon spin qubits have emerged as a promising path to large-scale quantum processors. In this prospect, the development of scalable qubit readout schemes involving a minimal device overhead is a compelling step. Here we report the implementation of gate-coupled rf reflectometry for the dispersive readout of a fully functional spin qubit device. We use a p-type double-gate transistor made using industry-standard silicon technology. The first gate confines a hole quantum dot encoding the spin qubit, the second one a helper dot enabling readout. The qubit state is measured through the phase response of a lumped-element resonator to spin-selective interdot tunneling. The demonstrated qubit readout scheme requires no coupling to a Fermi reservoir, thereby offering a compact and potentially scalable solution whose operation may be extended above 1 K.

2.
Phys Rev Lett ; 121(2): 027701, 2018 Jul 13.
Artículo en Inglés | MEDLINE | ID: mdl-30085716

RESUMEN

Quantum shot noise probes the dynamics of charge transfers through a quantum conductor, reflecting whether quasiparticles flow across the conductor in a steady stream, or in syncopated bursts. We have performed high-sensitivity shot noise measurements in a quantum dot obtained in a silicon metal-oxide-semiconductor field-effect transistor. The quality of our device allows us to precisely associate the different transport regimes and their statistics with the internal state of the quantum dot. In particular, we report on large current fluctuations in the inelastic cotunneling regime, corresponding to different highly correlated, non-Markovian charge transfer processes. We have also observed unusually large current fluctuations at low energy in the elastic cotunneling regime, the origin of which remains to be fully investigated.

3.
Nat Commun ; 7: 13575, 2016 11 24.
Artículo en Inglés | MEDLINE | ID: mdl-27882926

RESUMEN

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 encoding a hole spin qubit, the second one a quantum dot used for the qubit read-out. All electrical, two-axis control of the spin qubit is achieved by applying a phase-tunable microwave modulation to the first gate. The demonstrated qubit functionality in a basic transistor-like device constitutes a promising step towards the elaboration of scalable spin qubit geometries in a readily exploitable CMOS platform.

4.
Phys Rev Lett ; 116(13): 136801, 2016 Apr 01.
Artículo en Inglés | MEDLINE | ID: mdl-27081995

RESUMEN

The Kondo effect is the many-body screening of a local spin by a cloud of electrons at very low temperature. It has been proposed as an explanation of the zero-bias anomaly in quantum point contacts where interactions drive a spontaneous charge localization. However, the Kondo origin of this anomaly remains under debate, and additional experimental evidence is necessary. Here we report on the first phase-sensitive measurement of the zero-bias anomaly in quantum point contacts using a scanning gate microscope to create an electronic interferometer. We observe an abrupt shift of the interference fringes by half a period in the bias range of the zero-bias anomaly, a behavior which cannot be reproduced by single-particle models. We instead relate it to the phase shift experienced by electrons scattering off a Kondo system. Our experiment therefore provides new evidence of this many-body effect in quantum point contacts.

5.
Nano Lett ; 16(1): 88-92, 2016 Jan 13.
Artículo en Inglés | MEDLINE | ID: mdl-26599868

RESUMEN

Hole spins in silicon represent a promising yet barely explored direction for solid-state quantum computation, possibly combining long spin coherence, resulting from a reduced hyperfine interaction, and fast electrically driven qubit manipulation. Here we show that a silicon-nanowire field-effect transistor based on state-of-the-art silicon-on-insulator technology can be operated as a few-hole quantum dot. A detailed magnetotransport study of the first accessible hole reveals a g-factor with unexpectedly strong anisotropy and gate dependence. We infer that these two characteristics could enable an electrically driven g-tensor-modulation spin resonance with Rabi frequencies exceeding several hundred mega-Hertz.

6.
Nano Lett ; 15(7): 4622-7, 2015 Jul 08.
Artículo en Inglés | MEDLINE | ID: mdl-26047255

RESUMEN

We report the dispersive readout of the spin state of a double quantum dot formed at the corner states of a silicon nanowire field-effect transistor. Two face-to-face top-gate electrodes allow us to independently tune the charge occupation of the quantum dot system down to the few-electron limit. We measure the charge stability of the double quantum dot in DC transport as well as dispersively via in situ gate-based radio frequency reflectometry, where one top-gate electrode is connected to a resonator. The latter removes the need for external charge sensors in quantum computing architectures and provides a compact way to readout the dispersive shift caused by changes in the quantum capacitance during inter-dot charge transitions. Here, we observe Pauli spin-blockade in the high-frequency response of the circuit at finite magnetic fields between singlet and triplet states. The blockade is lifted at higher magnetic fields when intra-dot triplet states become the ground state configuration. A line shape analysis of the dispersive phase shift reveals furthermore an intra-dot valley-orbit splitting Δvo of 145 µeV. Our results open up the possibility to operate compact complementary metal-oxide semiconductor (CMOS) technology as a singlet-triplet qubit and make split-gate silicon nanowire architectures an ideal candidate for the study of spin dynamics.

7.
J Phys Condens Matter ; 27(15): 154206, 2015 Apr 22.
Artículo en Inglés | MEDLINE | ID: mdl-25783566

RESUMEN

We describe the first implementation of a coupled atom transistor where two shallow donors (P or As) are implanted in a nanoscale silicon nanowire and their electronic levels are controlled with three gate voltages. Transport spectroscopy through these donors placed in series is performed both at zero and microwave frequencies. The coherence of the charge transfer between the two donors is probed by Landau-Zener-Stückelberg interferometry. Single-charge transfer at zero bias (electron pumping) has been performed and the crossover between the adiabatic and non-adiabatic regimes is studied.

8.
Nat Commun ; 5: 4290, 2014 Jun 30.
Artículo en Inglés | MEDLINE | ID: mdl-24978440

RESUMEN

Quantum point contacts exhibit mysterious conductance anomalies in addition to well-known conductance plateaus at multiples of 2e(2)/h. These 0.7 and zero-bias anomalies have been intensively studied, but their microscopic origin in terms of many-body effects is still highly debated. Here we use the charged tip of a scanning gate microscope to tune in situ the electrostatic potential of the point contact. While sweeping the tip distance, we observe repetitive splittings of the zero-bias anomaly, correlated with simultaneous appearances of the 0.7 anomaly. We interpret this behaviour in terms of alternating equilibrium and non-equilibrium Kondo screenings of different spin states localized in the channel. These alternating Kondo effects point towards the presence of a Wigner crystal containing several charges with different parities. Indeed, simulations show that the electron density in the channel is low enough to reach one-dimensional Wigner crystallization over a size controlled by the tip position.

9.
Phys Rev Lett ; 110(13): 136802, 2013 Mar 29.
Artículo en Inglés | MEDLINE | ID: mdl-23581354

RESUMEN

We report on microwave-driven coherent electron transfer between two coupled donors embedded in a silicon nanowire. By increasing the microwave frequency we observe a transition from incoherent to coherent driving revealed by the emergence of a Landau-Zener-Stückelberg quantum interference pattern of the measured current through the donors. This interference pattern is fitted to extract characteristic parameters of the double-donor system. In particular we estimate a charge dephasing time of 0.3±0.1 ns, comparable to other types of charge-based two-level systems. The demonstrated coherent coupling between two dopants is an important step towards donor-based quantum computing devices in silicon.

10.
Nat Commun ; 4: 1581, 2013.
Artículo en Inglés | MEDLINE | ID: mdl-23481389

RESUMEN

With the development of single-atom transistors, consisting of single dopants, nanofabrication has reached an extreme level of miniaturization. Promising functionalities for future nanoelectronic devices are based on the possibility of coupling several of these dopants to each other. This already allowed to perform spectroscopy of the donor state by d.c. electrical transport. The next step, namely manipulating a single electron over two dopants, remains a challenge. Here we demonstrate electron pumping through two phosphorus donors in series implanted in a silicon nanowire. While quantized pumping is achieved in the low-frequency adiabatic regime, we observe remarkable features at higher frequency when the charge transfer is limited either by the tunnelling rates to the electrodes or between the two donors. The transitions between quantum states are modelled involving a Landau-Zener transition, allowing to reproduce in detail the characteristic signatures observed in the non-adiabatic regime.

11.
Phys Rev Lett ; 108(20): 206812, 2012 May 18.
Artículo en Inglés | MEDLINE | ID: mdl-23003174

RESUMEN

We measure a large valley-orbit splitting for shallow isolated phosphorus donors in a silicon gated nanowire. This splitting is close to the bulk value and well above previous reports in silicon nanostructures. It was determined using a double dopant transport spectroscopy which eliminates artifacts induced by the environment. Quantitative simulations taking into account the position of the donors with respect to the Si/SiO2 interface and electric field in the wire show that the values found are consistent with the device geometry.

12.
Med Trop (Mars) ; 72 Spec No: 66-71, 2012 Mar.
Artículo en Inglés | MEDLINE | ID: mdl-22693932

RESUMEN

The outbreak of chikungunya that occurred on French Island territories in the southwest Indian Ocean in 2005 and 2006 caused severe morbidity and mortality. In the aftermath, French authorities set up a scientific task force including experts in epidemiology, public health, entomology, virology, immunology, sociology, animal health, community and hospital medicine. The mission of the task force was to conceive and propose research programs needed to increase understanding of the disease and epidemic and to help public health officials in improving epidemic response measures. The purpose of this article is to describe the findings of the task force at the end of its two-year existence and initial outcomes in the the areas studied. Discussion emphasizes topics requiring further study.


Asunto(s)
Infecciones por Alphavirus/prevención & control , Control de Enfermedades Transmisibles/organización & administración , Brotes de Enfermedades/prevención & control , Grupo de Atención al Paciente/organización & administración , Aedes/fisiología , Aedes/virología , Infecciones por Alphavirus/epidemiología , Animales , Fiebre Chikungunya , Ensayos Clínicos como Asunto , Francia/epidemiología , Humanos , Islas del Oceano Índico/epidemiología , Biología Molecular
13.
Nat Nanotechnol ; 5(2): 133-7, 2010 Feb.
Artículo en Inglés | MEDLINE | ID: mdl-19966793

RESUMEN

One consequence of the continued downward scaling of transistors is the reliance on only a few discrete atoms to dope the channel, and random fluctuations in the number of these dopants are already a major issue in the microelectronics industry. Although single dopant signatures have been observed at low temperatures, the impact on transistor performance of a single dopant atom at room temperature is not well understood. Here, we show that a single arsenic dopant atom dramatically affects the off-state room-temperature behaviour of a short-channel field-effect transistor fabricated with standard microelectronics processes. The ionization energy of the dopant is measured to be much larger than it is in bulk, due to its proximity to the buried oxide, and this explains the large current below threshold and large variability in ultra-scaled transistors. The results also suggest a path to incorporating quantum functionalities into silicon CMOS devices through manipulation of single donor orbitals.


Asunto(s)
Electroquímica/métodos , Nanoestructuras/química , Nanotecnología/métodos , Simulación por Computador , Cristalización , Electroquímica/instrumentación , Electrónica/instrumentación , Tamaño de la Partícula , Silicio/química , Propiedades de Superficie , Temperatura , Termodinámica , Transistores Electrónicos
14.
Phys Rev Lett ; 101(15): 157006, 2008 Oct 10.
Artículo en Inglés | MEDLINE | ID: mdl-18999631

RESUMEN

Scanning tunneling spectroscopy at very low temperatures on homogeneously disordered superconducting titanium nitride thin films reveals strong spatial inhomogeneities of the superconducting gap Delta in the density of states. Upon increasing disorder, we observe suppression of the superconducting critical temperature Tc towards zero, enhancement of spatial fluctuations in Delta, and growth of the Delta/Tc ratio. These findings suggest that local superconductivity survives across the disorder-driven superconductor-insulator transition.

15.
Phys Rev Lett ; 99(11): 117002, 2007 Sep 14.
Artículo en Inglés | MEDLINE | ID: mdl-17930462

RESUMEN

We present current noise measurements in a long diffusive superconductor-normal-metal-superconductor junction in the low voltage regime, in which transport can be partially described in terms of coherent multiple Andreev reflections. We show that, when decreasing voltage, the current noise exhibits a strong divergence together with a broad peak. We ascribe this peak to the mixing between the ac-Josephson current and the noise of the junction itself. We show that the junction noise corresponds to the thermal noise of a nonlinear resistor 4k B T/R with R=V/I(V) and no adjustable parameters.

16.
Phys Rev Lett ; 90(6): 067002, 2003 Feb 14.
Artículo en Inglés | MEDLINE | ID: mdl-12633318

RESUMEN

We performed low temperature shot noise measurements in superconductor (TiN) strongly disordered normal metal (heavily doped Si) weakly transparent junctions. We show that the conductance has a maximum due to coherent multiple Andreev reflections at low energy and that the shot noise is then twice the Poisson noise (S = 4eI). When the subgap conductance reaches its minimum at finite voltage the shot noise changes to the normal value (S = 2eI) due to a large quasiparticle contribution.

17.
Nature ; 405(6782): 50-3, 2000 May 04.
Artículo en Inglés | MEDLINE | ID: mdl-10811213

RESUMEN

Shot noise refers to the fluctuations in electrical current through a device arising from the discrete nature of the charge-carrying particles. Recent experiments have exploited the fact that the shot noise is proportional to the charge of the carriers to establish fractional quantization of quasiparticles in the fractional quantum Hall effect. By a similar argument, it is expected that when a superconducting reservoir emits Cooper pairs, (which have a charge twice that of an electron) into a short normal-metal wire, the shot noise should be double that obtained for a normal-metal reservoir. Although the charge of Cooper pairs has been well established by flux quantization and tunnel experiments, doubling of their shot noise has not yet been observed. Here we report a shot-noise experiment using a short diffusive normal-metal superconductor contact, in which we confirm the predicted noise behaviour for double charges. The measurements, taken over a large range of bias current, establish that phase coherence is not required to observe the effect.

18.
Phys Rev B Condens Matter ; 53(3): 973-976, 1996 Jan 15.
Artículo en Inglés | MEDLINE | ID: mdl-9983532
19.
Phys Rev Lett ; 75(21): 3902-3905, 1995 Nov 20.
Artículo en Inglés | MEDLINE | ID: mdl-10059760
SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA
...