Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 14 de 14
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 ; 120(16): 167201, 2018 Apr 20.
Artículo en Inglés | MEDLINE | ID: mdl-29756906

RESUMEN

We report the observation of spin-to-charge current conversion in strained mercury telluride at room temperature, using spin pumping experiments. We show that a HgCdTe barrier can be used to protect the HgTe from direct contact with the ferromagnet, leading to very high conversion rates, with inverse Edelstein lengths up to 2.0±0.5 nm. The influence of the HgTe layer thickness on the conversion efficiency is found to differ strongly from what is expected in spin Hall effect systems. These measurements, associated with the temperature dependence of the resistivity, suggest that these high conversion rates are due to the spin momentum locking property of HgTe surface states.

3.
Rev Med Interne ; 39(2): 84-89, 2018 Feb.
Artículo en Francés | MEDLINE | ID: mdl-29279179

RESUMEN

INTRODUCTION: In France, nearly 50% of patients transfused in packed red blood cells are 75 or older. The benefit of restrictive transfusion policies is no longer to be demonstrated, but the practices are still far from it. The objective of our study was to show the impact of a decision support tool on transfusion practices, specifically in a hospitalized elderly population. METHOD: A clinical decision support, validated in the improvement of practices, was created, based on the latest transfusion recommendations of 2014. Our study was interventional, monocentric, within the departments of internal medicine and geriatrics of a university hospital from February to July 2016. The clinical decision support was available for any request of transfusion of packed red blood cells for 75 years old or older patient who was hospitalized in one of these two services. RESULTS: There were 134 transfusions out of 173 for which the prescriber used our tool. Comparing 2016 with the previous two years, our tool decreased the rate of packed red blood cells delivered by 11% compared to 2014 (P<0.005), but there was no significant difference compared to 2015. It has also reduced the transfusion rate of multi-unit transfusions by 35% compared with 2014 and by 29% compared with 2015 (P<0.005). CONCLUSION: Our tool, applied specifically to the elderly, is useful to improve transfusion practices and requires to be validated on a larger scale.


Asunto(s)
Sistemas de Apoyo a Decisiones Clínicas/estadística & datos numéricos , Transfusión de Eritrocitos/estadística & datos numéricos , Pautas de la Práctica en Medicina/estadística & datos numéricos , Anciano , Anciano de 80 o más Años , Transfusión de Eritrocitos/métodos , Femenino , Geriatría , Hospitalización , Humanos , Masculino
4.
Nat Commun ; 8(1): 501, 2017 09 11.
Artículo en Inglés | MEDLINE | ID: mdl-28894092

RESUMEN

Controlling nanocircuits at the single electron spin level is a possible route for large-scale quantum information processing. In this context, individual electron spins have been identified as versatile quantum information carriers to interconnect different nodes of a spin-based semiconductor quantum circuit. Despite extensive experimental efforts to control the electron displacement over long distances, maintaining electron spin coherence after transfer remained elusive up to now. Here we demonstrate that individual electron spins can be displaced coherently over a distance of 5 µm. This displacement is realized on a closed path made of three tunnel-coupled lateral quantum dots at a speed approaching 100 ms-1. We find that the spin coherence length is eight times longer than expected from the electron spin coherence without displacement, pointing at a process similar to motional narrowing observed in nuclear magnetic resonance experiments. The demonstrated coherent displacement will open the route towards long-range interaction between distant spin qubits.The spin states of electrons in quantum dots have well-established potential for use as qubits but some proposed developments require the ability to move the quantum spin state across a larger device. Here, the authors experimentally demonstrate coherent shuttling of spins in a ring of three dots.

5.
Nat Nanotechnol ; 11(8): 672-6, 2016 08.
Artículo en Inglés | MEDLINE | ID: mdl-27240417

RESUMEN

Transporting ensembles of electrons over long distances without losing their spin polarization is an important benchmark for spintronic devices. It usually requires injecting and probing spin-polarized electrons in conduction channels using ferromagnetic contacts or optical excitation. In parallel with this development, important efforts have been dedicated to achieving control of nanocircuits at the single-electron level. The detection and coherent manipulation of the spin of a single electron trapped in a quantum dot are now well established. Combined with the recently demonstrated control of the displacement of individual electrons between two distant quantum dots, these achievements allow the possibility of realizing spintronic protocols at the single-electron level. Here, we demonstrate that spin information carried by one or two electrons can be transferred between two quantum dots separated by a distance of 4 µm with a classical fidelity of 65%. We show that at present it is limited by spin flips occurring during the transfer procedure before and after electron displacement. Being able to encode and control information in the spin degree of freedom of a single electron while it is being transferred over distances of a few micrometres on nanosecond timescales will pave the way towards 'quantum spintronics' devices, which could be used to implement large-scale spin-based quantum information processing.

6.
Phys Rev Lett ; 113(12): 126601, 2014 Sep 19.
Artículo en Inglés | MEDLINE | ID: mdl-25279636

RESUMEN

We report on the direct observation of the transmission phase shift through a Kondo correlated quantum dot by employing a new type of two-path interferometer. We observed a clear π/2-phase shift, which persists up to the Kondo temperature TK. Above this temperature, the phase shifts by more than π/2 at each Coulomb peak, approaching the behavior observed for the standard Coulomb blockade regime. These observations are in remarkable agreement with two-level numerical renormalization group calculations. The unique combination of experimental and theoretical results presented here fully elucidates the phase evolution in the Kondo regime.

7.
Nat Commun ; 2: 556, 2011 Nov 22.
Artículo en Inglés | MEDLINE | ID: mdl-22109530

RESUMEN

Artificial molecules containing just one or two electrons provide a powerful platform for studies of orbital and spin quantum dynamics in nanoscale devices. A well-known example of these dynamics is tunnelling of electrons between two coupled quantum dots triggered by microwave irradiation. So far, these tunnelling processes have been treated as electric-dipole-allowed spin-conserving events. Here we report that microwaves can also excite tunnelling transitions between states with different spin. We show that the dominant mechanism responsible for violation of spin conservation is the spin-orbit interaction. These transitions make it possible to perform detailed microwave spectroscopy of the molecular spin states of an artificial hydrogen molecule and open up the possibility of realizing full quantum control of a two-spin system through microwave excitation.

8.
Phys Rev Lett ; 102(22): 226801, 2009 Jun 05.
Artículo en Inglés | MEDLINE | ID: mdl-19658885

RESUMEN

We present phase coherence time measurements in quasi-one-dimensional mesoscopic wires made from high mobility two-dimensional electron gas. By implanting gallium ions into a GaAs/AlGaAs heterojunction we are able to vary the diffusion coefficient over 2 orders of magnitude. We show that in the diffusive limit, the decoherence time follows a power law as a function of diffusion coefficient as expected by theory. When the disorder is low enough so that the samples are semiballistic, we observe a new and unexpected regime in which the phase coherence time is independent of disorder. In addition, for all samples the temperature dependence of the phase coherence time follows a power law down to the lowest temperatures without any sign of saturation and this strongly suggests that the frequently observed low temperature saturation is not intrinsic.

9.
Phys Rev Lett ; 98(12): 126601, 2007 Mar 23.
Artículo en Inglés | MEDLINE | ID: mdl-17501146

RESUMEN

We observe an experimental signature of the role of phonons in spin relaxation between triplet and singlet states in a two-electron quantum dot. Using both the external magnetic field and the electrostatic confinement potential, we change the singlet-triplet energy splitting from 1.3 meV to zero and observe that the spin relaxation time depends nonmonotonously on the energy splitting. A simple theoretical model is derived to capture the underlying physical mechanism. The present experiment confirms that spin-flip energy is dissipated in the phonon bath.

10.
Nature ; 442(7104): 766-71, 2006 Aug 17.
Artículo en Inglés | MEDLINE | ID: mdl-16915280

RESUMEN

The ability to control the quantum state of a single electron spin in a quantum dot is at the heart of recent developments towards a scalable spin-based quantum computer. In combination with the recently demonstrated controlled exchange gate between two neighbouring spins, driven coherent single spin rotations would permit universal quantum operations. Here, we report the experimental realization of single electron spin rotations in a double quantum dot. First, we apply a continuous-wave oscillating magnetic field, generated on-chip, and observe electron spin resonance in spin-dependent transport measurements through the two dots. Next, we coherently control the quantum state of the electron spin by applying short bursts of the oscillating magnetic field and observe about eight oscillations of the spin state (so-called Rabi oscillations) during a microsecond burst. These results demonstrate the feasibility of operating single-electron spins in a quantum dot as quantum bits.

11.
Phys Rev Lett ; 94(11): 113601, 2005 Mar 25.
Artículo en Inglés | MEDLINE | ID: mdl-15903855

RESUMEN

We present an efficient, state-selective, nondemolition atom-counting procedure based on the dispersive interaction of a sample of circular Rydberg atoms with a mesoscopic field contained in a high-quality superconducting cavity. The state-dependent atomic index of refraction, proportional to the atom number, shifts the classical field phase. A homodyne procedure translates the information from the phase to the intensity. The final field intensity is readout by a mesoscopic atomic sample. This method opens promising routes for quantum information processing and nonclassical state generation with Rydberg atoms.

12.
Phys Rev Lett ; 94(1): 010401, 2005 Jan 14.
Artículo en Inglés | MEDLINE | ID: mdl-15698050

RESUMEN

Using an echo technique proposed by Morigi et al., we have time-reversed the atom-field interaction in a cavity quantum electrodynamics experiment. The collapse of the atomic Rabi oscillation in a coherent field is reversed, resulting in an induced revival signal. The amplitude of this "echo" is sensitive to nonunitary decoherence processes. Its observation demonstrates the existence of a mesoscopic quantum superposition of field states in the cavity between the collapse and the revival times.

13.
Phys Rev Lett ; 91(23): 230405, 2003 Dec 05.
Artículo en Inglés | MEDLINE | ID: mdl-14683167

RESUMEN

We observe that a mesoscopic field made of several tens of microwave photons exhibits quantum features when interacting with a single Rydberg atom in a high-Q cavity. The field is split into two components whose phases differ by an angle inversely proportional to the square root of the average photon number. The field and the atomic dipole are phase entangled. These manifestations of photon graininess vanish at the classical limit. This experiment opens the way to studies of large quantum state superpositions at the quantum-classical boundary.

14.
Phys Rev Lett ; 89(20): 200402, 2002 Nov 11.
Artículo en Inglés | MEDLINE | ID: mdl-12443461

RESUMEN

We have measured the complete Wigner function W of the vacuum and of a single-photon state for a field stored in a high-Q cavity. This experiment implements the direct Lutterbach and Davidovich method [L. G. Lutterbach and L. Davidovich, Phys. Rev. Lett. 78, 2547 (1997)]] and is based on the dispersive interaction of a single circular Rydberg atom with the cavity field. The nonclassical nature of the single-photon field is exhibited by a region of negative W values. Extensions to other nonclassical cavity field states are discussed.

SELECCIÓN DE REFERENCIAS
DETALLE DE LA BÚSQUEDA
...