112 research outputs found
Exact diagonalization of the Hubbard model on graphics processing units
We solve the Hubbard model with the exact diagonalization method on a
graphics processing unit (GPU). We benchmark our GPU program against a
sequential CPU code by using the Lanczos algorithm to solve the ground state
energy in two cases: a one-dimensional ring and a two-dimensional square
lattice. In the one-dimensional case, we obtain speedups of over 100 and 60 in
single and double precision arithmetic, respectively. In the two-dimensional
case, the corresponding speedups are over 110 and 70
Obtaining localization properties efficiently using the Kubo-Greenwood formalism
We establish, through numerical calculations and comparisons with a recursive
Green's function based implementation of the Landauer-B\"uttiker formalism, an
efficient method for studying Anderson localization in quasi-one-dimensional
and two-dimensional systems using the Kubo-Greenwood formalism. Although the
recursive Green's function method can be used to obtain the localization length
of a mesoscopic conductor, it is numerically very expensive for systems that
contain a large number of atoms transverse to the transport direction. On the
other hand, linear-scaling has been achieved with the Kubo-Greenwood method,
enabling the study of effectively two-dimensional systems. While the
propagating length of the charge carriers will eventually saturate to a finite
value in the localized regime, the conductances given by the Kubo-Greenwood
method and the recursive Green's function method agree before the saturation.
The converged value of the propagating length is found to be directly
proportional to the localization length obtained from the exponential decay of
the conductance.Comment: 7 pages, 6 figure
Charge-noise tolerant exchange gates of singlet-triplet qubits in asymmetric double quantum dots
In the semi-conductor double quantum dot singlet-triplet qubit architecture,
the decoherence caused by the qubit's charge environment poses a serious
obstacle in the way towards large scale quantum computing. The effects of the
charge decoherence can be mitigated by operating the qubit in the so called
sweet spot regions where it is insensitive to electrical noise. In this paper,
we propose singlet-triplet qubits based on two quantum dots of different sizes.
Such asymmetric double dot systems allow the implementation of exchange gates
with controllable exchange splitting operated in the doubly occupied charge
region of the larger dot, where the qubit has high resilience to charge noise.
In the larger dot, can be quenched to a value smaller than the intra-dot
tunneling using magnetic fields, while the smaller dot and its larger splitting
can be used in the projective readout of the qubit
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