20,873 research outputs found
Hybridized solid-state qubit in the charge-flux regime
Most superconducting qubits operate in a regime dominated by either the
electrical charge or the magnetic flux. Here we study an intermediate case: a
hybridized charge-flux qubit with a third Josephson junction (JJ) added into
the SQUID loop of the Cooper-pair box. This additional JJ allows the optimal
design of a low-decoherence qubit. Both charge and flux noises are
considered. Moreover, we show that an efficient quantum measurement of either
the current or the charge can be achieved by using different area sizes for the
third JJ.Comment: 7 pages, 5 figures. Phys. Rev. B, in pres
A Simplified Scheme of Estimation and Cancellation of Companding Noise for Companded Multicarrier Transmission Systems
Nonlinear companding transform is an efficient method to reduce the high peak-to-average power ratio (PAPR) of multicarrier transmission systems. However, the introduced companding noise greatly degrades the bit-error-rate (BER) performance of the companded multicarrier systems. In this paper, a simplified but effective scheme of estimation and cancellation of companding noise for the companded multicarrier transmission system is proposed. By expressing the companded signals as the summation of original signals added with a companding noise component, and subtracting this estimated companding noise from the received signals, the BER performance of the overall system can be significantly improved. Simulation results well confirm the great advantages of the proposed scheme over other conventional decompanding or no decompanding schemes under various situations
Scalable quantum computing with Josephson charge qubits
A goal of quantum information technology is to control the quantum state of a
system, including its preparation, manipulation, and measurement. However,
scalability to many qubits and controlled connectivity between any selected
qubits are two of the major stumbling blocks to achieve quantum computing (QC).
Here we propose an experimental method, using Josephson charge qubits, to
efficiently solve these two central problems. The proposed QC architecture is
scalable since any two charge qubits can be effectively coupled by an
experimentally accessible inductance. More importantly, we formulate an
efficient and realizable QC scheme that requires only one (instead of two or
more) two-bit operation to implement conditional gates.Comment: 4 pages, 2 figure
Effective size of a trapped atomic Bose gas
We investigate the temperature-dependent effective size of a trapped
interacting atomic Bose gas within a mean field theory approximation. The
sudden shrinking of the average length, as observed in an earlier experiment by
Wang {\it et al.} [Chin. Phys. Lett. {\bf 20}, 799 (2003)], is shown to be a
good indication for Bose-Einstein condensation (BEC). Our study also supports
the use of the average width of a trapped Bose gas for a nondestructive
calibration of its temperature.Comment: RevTex4, 6 pages, 4 eps figures, to appear in Phys. Rev.
Creating maximally entangled atomic states in a Bose-Einstein condensate
We propose a protocol to create maximally entangled pairs, triplets,
quartiles, and other clusters of Bose condensed atoms starting from a
condensate in the Mott insulator state. The essential element is to drive
single atom Raman transitions using laser pulses. Our scheme is simple,
efficient, and can be readily applied to the recent experimental system as
reported by Greiner {\it et al.} [ Nature {\bf 413}, 44 (2002)].Comment: 4 pages, 2 figures. revised version as to be publishe
Low-decoherence flux qubit
A flux qubit can have a relatively long decoherence time at the degeneracy
point, but away from this point the decoherence time is greatly reduced by
dephasing. This limits the practical applications of flux qubits. Here we
propose a new qubit design modified from the commonly used flux qubit by
introducing an additional capacitor shunted in parallel to the smaller
Josephson junction (JJ) in the loop. Our results show that the effects of noise
can be considerably suppressed, particularly away from the degeneracy point, by
both reducing the coupling energy of the JJ and increasing the shunt
capacitance. This shunt capacitance provides a novel way to improve the qubit.Comment: 4 pages, 4 figure
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