1,966 research outputs found
Global control and fast solid-state donor electron spin quantum computing
We propose a scheme for quantum information processing based on donor
electron spins in semiconductors, with an architecture complementary to the
original Kane proposal. We show that a naive implementation of electron spin
qubits provides only modest improvement over the Kane scheme, however through
the introduction of global gate control we are able to take full advantage of
the fast electron evolution timescales. We estimate that the latent clock speed
is 100-1000 times that of the nuclear spin quantum computer with the ratio
approaching the level.Comment: 9 pages, 9 figure
A Comparison of N\u3csub\u3e2\u3c/sub\u3eO Emissions After Application of Dairy Slurry on Perennial Grass or Bare Soil Prior to Planting an Annual Crop in Coastal British Columbia, Canada
Because of restrictions on land application of manure in autumn and winter, dairy farmers in coastal British Columbia (BC) must apply half of their annual manure supply from mid-Feb. to mid-April. Although two thirds of their land is in perennial grass, most of this manure is applied to bare soil, usually maize land, prior to planting. This is done for convenience and to avoid damaging grass stands with equipment traffic. Farmers are encouraged to allocate more manure to grass to minimise soil NO3 concentrations after maize harvest, because maize takes up less N than grass, and the bare fields after harvest are subject to wintertime leaching. However, the effect of this practice on emissions of N2O is not known. Our objective was to compare the effect of spring application of manure on bare land and on grass with respect to emissions of N2O. A second objective was to compare early, late and split applications of manure
Second Harmonic Coherent Driving of a Spin Qubit in a Si/SiGe Quantum Dot
We demonstrate coherent driving of a single electron spin using second
harmonic excitation in a Si/SiGe quantum dot. Our estimates suggest that the
anharmonic dot confining potential combined with a gradient in the transverse
magnetic field dominates the second harmonic response. As expected, the Rabi
frequency depends quadratically on the driving amplitude and the periodicity
with respect to the phase of the drive is twice that of the fundamental
harmonic. The maximum Rabi frequency observed for the second harmonic is just a
factor of two lower than that achieved for the first harmonic when driving at
the same power. Combined with the lower demands on microwave circuitry when
operating at half the qubit frequency, these observations indicate that second
harmonic driving can be a useful technique for future quantum computation
architectures.Comment: 9 pages, 9 figure
Identifying single electron charge sensor events using wavelet edge detection
The operation of solid-state qubits often relies on single-shot readout using
a nanoelectronic charge sensor, and the detection of events in a noisy sensor
signal is crucial for high fidelity readout of such qubits. The most common
detection scheme, comparing the signal to a threshold value, is accurate at low
noise levels but is not robust to low-frequency noise and signal drift. We
describe an alternative method for identifying charge sensor events using
wavelet edge detection. The technique is convenient to use and we show that,
with realistic signals and a single tunable parameter, wavelet detection can
outperform thresholding and is significantly more tolerant to 1/f and
low-frequency noise.Comment: 11 pages, 4 figure
A programmable two-qubit quantum processor in silicon
With qubit measurement and control fidelities above the threshold of
fault-tolerance, much attention is moving towards the daunting task of scaling
up the number of physical qubits to the large numbers needed for fault tolerant
quantum computing. Here, quantum dot based spin qubits may offer significant
advantages due to their potential for high densities, all-electrical operation,
and integration onto an industrial platform. In this system, the
initialisation, readout, single- and two-qubit gates have been demonstrated in
various qubit representations. However, as seen with other small scale quantum
computer demonstrations, combining these elements leads to new challenges
involving qubit crosstalk, state leakage, calibration, and control hardware
which provide invaluable insight towards scaling up. Here we address these
challenges and demonstrate a programmable two-qubit quantum processor in
silicon by performing both the Deutsch-Josza and the Grover search algorithms.
In addition, we characterise the entanglement in our processor through quantum
state tomography of Bell states measuring state fidelities between 85-89% and
concurrences between 73-80%. These results pave the way for larger scale
quantum computers using spins confined to quantum dots
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