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.
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
. 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.
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.
Abstract
Semiconductor spin qubits based on spin–orbit states are responsive to electric field excitations, allowing for practical, fast and potentially scalable qubit control. Spin electric ...susceptibility, however, renders these qubits generally vulnerable to electrical noise, which limits their coherence time. Here we report on a spin–orbit qubit consisting of a single hole electrostatically confined in a natural silicon metal-oxide-semiconductor device. By varying the magnetic field orientation, we reveal the existence of operation sweet spots where the impact of charge noise is minimized while preserving an efficient electric-dipole spin control. We correspondingly observe an extension of the Hahn-echo coherence time up to 88 μs, exceeding by an order of magnitude existing values reported for hole spin qubits, and approaching the state-of-the-art for electron spin qubits with synthetic spin–orbit coupling in isotopically purified silicon. Our finding enhances the prospects of silicon-based hole spin qubits for scalable quantum information processing.
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.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
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.
The hydrographical and dynamical properties of the upwelling filaments forming off Cap Blanc (Mauritania) are investigated using remotely sensed and in situ data collected in April/May 2009 during ...the strongest upwelling season. The area is situated at the southern edge of the NW African upwelling system, where the Cape Verde Frontal Zone (CVFZ) separates warmer, saltier North Atlantic Central Water (NACW) and cooler, fresher South Atlantic Central Water (SACW). Sea surface temperature images indicated the presence of an upwelling filament extending >280 km offshore, rooted over the Cap Blanc promontory and entrained around a warm‐core anticyclonic eddy. After this filament started to decay, a new cold filament developed at the approximate same location. High resolution Moving Vessel Profiler (MVP) and Acoustic Doppler Current Profiler (ADCP) surveys of these mesoscale structures revealed that both filaments were carrying South Atlantic Central Water (SACW) offshore through an intense jet‐like flow. Similarity of the relative vorticity structure across the filament with that of the tangent eddy suggested that the latter was responsible for the offshore current. Tracking of this eddy in altimetric data demonstrated that it originated from the CVFZ, as implied by its hydrographic structure. Altimetric data also revealed that another anticyclonic structure centered over the Cap Blanc promontory was responsible for the northwestward advection of SACW into the base of the filament. The results support the idea that some upwelling filaments can be produced by the interaction of an external eddy field, including topographic eddies, with the upwelled water.
Key Points
Upwelling filaments were surveyed in‐situ off Cap Blanc (Mauritania)
They are closely related to mesoscale eddies spawned by the Cape Verde Front
Topographic processes might also play a role in the filament formation
In this article, we have studied the drain current and transconductance of nMOS fully depleted silicon-on-insulator (FDSOI) transistors operating at low temperature (typically < 20 K) when back gate ...is forward biased. Humps appear in the current, leading to oscillations of the transconductance with gate voltage, owing to mobility discontinuity due to intersubband scattering, in relation with the 2-D subband structure. The conditions for which these specific features appear in thin-film silicon-on-insulator (SOI) devices have been analyzed, by varying the temperature, drain voltage, silicon channel thickness, and gate length.
This study presents the first continuous observations of Iceland Scotland Overflow Water (ISOW) passing through the Bight Fracture Zone (BFZ), the northernmost deep bathymetric channel across the ...Reykjanes Ridge between the Iceland and Irminger Basins in the subpolar North Atlantic. Data from two 2‐year moorings, measuring temperature, salinity, and current velocity from 2015 to 2017, along with a set of deep ISOW‐embedded RAFOS floats, are used to investigate ISOW transport and water property variability through the BFZ, as well as advective pathways between the Iceland and Irminger Basins. The mooring‐derived record‐mean ISOW transport through the BFZ was −0.59 ± 0.27 × 1e6 m3/s (westward) and varied seasonally with weaker transport in winter and stronger transport in summer. Flow direction of ISOW through the BFZ was consistently westward except in winter, when week‐long flow reversals were frequently observed. The previously reported subpolar North Atlantic freshening event of the 2010s is evident in the BFZ mooring records beginning about January 2017. About one‐quarter of floats deployed in ISOW at 1800‐m depth upstream in the Iceland Basin show a direct advective pathway into the BFZ that appears to be primarily determined by bathymetry. Another quarter of the floats crossed over the ridge to the Irminger Sea through other gaps prior to reaching the Charlie‐Gibbs Fracture Zone.
Plain Language Summary
The deep currents in the North Atlantic Ocean transport cold, dense waters from high latitudes southward as part of the climate‐relevant overturning circulation. Understanding of the pathways and transports of these currents is improving, but some knowledge gaps persist. This paper describes the first sustained measurements of the deep current transporting cold, dense water through a major gap in the shallow Mid‐Atlantic Ridge, called the Bight Fracture Zone (BFZ), during 2015–2017. The resulting estimate of the mean volume transport through BFZ (about 600,000 m3/s westward) helps to quantify the total amount of this dense water mass passing from the eastern to western North Atlantic and provides a benchmark for numerical simulations of the deep ocean circulation in this region. The measurements also revealed an apparent seasonal cycle in volume transport, and unexpected flow reversals, mostly in winter. In early 2017, a significant decrease in salinity was observed, indicating the arrival in the BFZ of a known large‐scale low‐salinity anomaly that has been circulating around the northern North Atlantic since about 2010. Taken together, the results add several pieces to the puzzle that is the complex deep ocean circulation of the North Atlantic.
Key Points
First time series of Iceland Scotland Overflow Water (ISOW) transport through the Bight Fracture Zone (BFZ) indicates mean of −0.6 ± 0.3 Sv (westward)
These year‐round observations of ISOW transport through the BFZ reveal, for the first time, wintertime flow reversals and an annual cycle
Deep floats show a direct advective pathway into the BFZ that appears most influenced by local bathymetry
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.
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