3,456 research outputs found
Scalable gate architecture for densely packed semiconductor spin qubits
We demonstrate a 12 quantum dot device fabricated on an undoped Si/SiGe
heterostructure as a proof-of-concept for a scalable, linear gate architecture
for semiconductor quantum dots. The device consists of 9 quantum dots in a
linear array and 3 single quantum dot charge sensors. We show reproducible
single quantum dot charging and orbital energies, with standard deviations less
than 20% relative to the mean across the 9 dot array. The single quantum dot
charge sensors have a charge sensitivity of 8.2 x 10^{-4} e/root(Hz) and allow
the investigation of real-time charge dynamics. As a demonstration of the
versatility of this device, we use single-shot readout to measure a spin
relaxation time T1 = 170 ms at a magnetic field B = 1 T. By reconfiguring the
device, we form two capacitively coupled double quantum dots and extract a
mutual charging energy of 200 microeV, which indicates that 50 GHz two-qubit
gate operation speeds are feasible
Mixed-State Entanglement and Quantum Teleportation through Noisy Channels
The quantum teleportation with noisy EPR state is discussed. Using an optimal
decomposition technique, we compute the concurrence, entanglement of formation
and Groverian measure for various noisy EPR resources. It is shown analytically
that all entanglement measures reduce to zero when , where
is an average fidelity between Alice and Bob. This fact indicates
that the entanglement is a genuine physical resource for the teleportation
process. This fact gives valuable clues on the optimal decomposition for
higher-qubit mixed states. As an example, the optimal decompositions for the
three-qubit mixed states are discussed by adopting a teleportation with W-stateComment: 18 pages, 4 figure
Tripartite Entanglement in Noninertial Frame
The tripartite entanglement is examined when one of the three parties moves
with a uniform acceleration with respect to other parties. As Unruh effect
indicates, the tripartite entanglement exhibits a decreasing behavior with
increasing the acceleration. Unlike the bipartite entanglement, however, the
tripartite entanglement does not completely vanish in the infinite acceleration
limit. If the three parties, for example, share the Greenberger-Horne-Zeilinger
or W-state initially, the corresponding -tangle, one of the measures for
tripartite entanglement, is shown to be or 0.176 in this
limit, respectively. This fact indicates that the tripartite quantum
information processing may be possible even if one of the parties approaches to
the Rindler horizon. The physical implications of this striking result are
discussed in the context of black hole physics.Comment: 19 pages, 5 figure
Attack of Many Eavesdroppers via Optimal Strategy in Quantum Cryptography
We examine a situation that eavesdroppers attack the Bennett-Brassard
cryptographic protocol via their own optimal and symmetric strategies.
Information gain and mutual information with sender for each eavesdropper are
explicitly derived. The receiver's error rate for the case of arbitrary
eavesdroppers can be derived using a recursive relation. Although first
eavesdropper can get mutual information without disturbance arising due to
other eavesdroppers, subsequent eavesdropping generally increases the
receiver's error rate. Other eavesdroppers cannot gain information on the input
signal sufficiently. As a result, the information each eavesdropper gains
becomes less than optimal one.Comment: 17 pages, 8 figure
Amplitude Damping for single-qubit System with single-qubit mixed-state Environment
We study a generalized amplitude damping channel when environment is
initially in the single-qubit mixed state. Representing the affine
transformation of the generalized amplitude damping by a three-dimensional
volume, we plot explicitly the volume occupied by the channels simulatable by a
single-qubit mixed-state environment. As expected, this volume is embedded in
the total volume by the channels which is simulated by two-qubit enviroment.
The volume ratio is approximately 0.08 which is much smaller than 3/8, the
volume ratio for generalized depolarizing channels.Comment: 13 pages, 2 figures incluided V2: homepage address is included in
reference V3: version to appear in J. Phys. A: Mathematical and Theoretica
Identifying the favored mutation in a positive selective sweep.
Most approaches that capture signatures of selective sweeps in population genomics data do not identify the specific mutation favored by selection. We present iSAFE (for "integrated selection of allele favored by evolution"), a method that enables researchers to accurately pinpoint the favored mutation in a large region (∼5 Mbp) by using a statistic derived solely from population genetics signals. iSAFE does not require knowledge of demography, the phenotype under selection, or functional annotations of mutations
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