共查询到20条相似文献,搜索用时 9 毫秒
1.
ZHAO Xu LIANG Xian-Ting 《理论物理通讯》2005,44(5):827-832
We investigate the short-time decoherence of a solid-state qubit under Ohmic noise at optimal operation points. The decoherence is analyzed by maximum norm of the deviation density operator. It is shown that at the temperature T = 3 mK, the loss of the fidelity due to decoherence is much smaller than the DiVincenzo low decoherence criterion, which means that the mode/may be an optimal candidate of qubit for quantum computation. 相似文献
2.
LI Zhi-Qiang LIANG Xian-Ting 《理论物理通讯》2008,50(7):77-80
In this paper we investigate an environmental effects to Josephson charge qubit (JCQ) when the environment is taken as the Ohmic bath. At first, we derive the master equation from a JCQ-bath model. Then we investigate the coefficients of the equations that describe the shift in frequency, diffusive, decoherence, and so on. It is shown that our result on decoherence agrees with experimental one very well as the time is short enough. 相似文献
3.
We investigate the entropy squeezing in the system of a superconducting charge qubit coupled to a single mode field. We find an exact solution of the Milburn equation for the system and discuss the influence of intrinsic decoherence on entropy squeezing. As a comparison, we also consider the variance squeezing. Our results show that in the absence of the intrinsic decoherence both entropy and variance squeezings have the same periodic properties of time,and occur at the same range of time. However, when the intrinsic decoherence is considered, we find that as the time going on the entropy squeezing disappears fast than the variance squeezing, there exists a range of time where entropy squeezing can occur but variance squeezing cannot. 相似文献
4.
We investigate the entropy squeezing in the system of a superconducting charge qubit coupled to a single mode field. We find an exact solution of the Milburn equation for the system and discuss the influence of intrinsic decoherence on entropy squeezing. As a comparison, we also consider the variance squeezing. Our results show that in the absence of the intrinsic decoherence both entropy and variance squeezings have the same periodic properties of time, and occur at the same range of time. However,
when the intrinsic decoherence is considered, we find that as the time
going on the entropy squeezing disappears fast than the variance squeezing, there exists a range of time where entropy squeezing can occur but
variance squeezing cannot. 相似文献
5.
When the nonlinearity of nanomechanical resonator is not negligible,the quantum decoherence of charge qubit is studied analytically.Using nonlinear Jaynes–Cummings model,one explores the possibility of being quantum data bus for nonlinear nanomechanical resonator,the nonlinearity destroys the dynamical quantum information-storage and maintains the revival of quantum coherence of charge qubit.With the calculation of decoherence factor,we demonstrate the influence of the nonlinearity of nanomechanical resonator on engineered decoherence of charge qubit. 相似文献
6.
When the nonlinearity of nanomechanical resonator is not negligible, the quantum decoherence of charge qubit is studied analytically. Using nonlinear Jaynes-Cummings model, one explores the possibility of being quantum data bus for nonlinear nanomechanical resonator, the nonlinearity destroys the dynamical quantum information-storage and maintains the revival of quantum coherence of charge qubit. With the calculation of decoherence factor, we demonstrate the influence of the nonlinearity of nanomechanical resonator on engineered decoherence of charge qubit. 相似文献
7.
We study the entanglement of the
superconducting charge qubit with the
quantized electromagnetic field in a microwave cavity. It can be controlled
dynamically by a classical external field threading the SQUID within the
charge qubit. Utilizing the controllable quantum entanglement, we can demonstrate the dynamic process of the quantum storage of information
carried by charge qubit. On the other hand, based on this engineered quantum
entanglement, we can also demonstrate a progressive decoherence of charge
qubit with quantum jump due to the coupling with the cavity field in
quasi-classical state. 相似文献
8.
Superconducting qubits are Josephson junction-based circuits that exhibit macroscopic quantum behavior and can be manipulated as artificial atoms.Benefiting from the well-developed technology of microfabrication and microwave engineering,superconducting qubits have great advantages in design flexibility,controllability,and scalability.Over the past decade,there has been rapid progress in the field,which greatly improved our understanding of qubit decoherence and circuit optimization.The single-qubit coherence time has been steadily raised to the order of 10 to 100μs,allowing for the demonstration of high-fidelity gate operations and measurement-based feedback control.Here we review recent progress in the coherence and readout of superconducting qubits. 相似文献
9.
In this paper the master equation method is used to calculate the
relaxation and decoherence times of a qubit. The results are beyond
Markovian approximation, where the noise spectrum is assumed to be
wide-band, so that they are valid for not only the wide- but also
the narrow-band noises, which may be the main decoherence source in
solid-state qubits. Moreover, for some special cases, analytical
results can be achieved, which are consistent with those derived by
others. 相似文献
10.
The decoherence of two initially entangled qubits coupled with a
squeezed vacuum cavity separately is investigated exactly. The
results show that, first, in principle, the disentanglement time
decreases with the increase of squeeze parameter r, due to the
augmenting of average photon number of every mode in the squeezed
vacuum cavity. Second, there appear entanglement revivals after the
complete disentanglement for the case of even parity initial Bell
state, while there occur the entanglement decrease and the
entanglement revival before the complete disentanglement for the
case of odd parity initial Bell state. The results are quite
different from those for the case of qubits in a vacuum cavity. 相似文献
11.
For a mesoscopic radio frequency superconducting quantum
interference device (rfSQUID), at a degeneracy point, the system
reduces to a quantum two-state system which can be used as a flux
qubit. When the noise environment is equivalent to a harmonic
oscillators bath, by virtue of an operator-norm measure for the
short time decoherence, this paper investigates the initial
decoherence of the flux qubit operating in the ohmic noise
environment and illustrates its property by means of the numerical
evaluation. 相似文献
12.
Ying-Hua Ji 《International Journal of Theoretical Physics》2008,47(9):2363-2371
In the Born-Markov approximation, a method that calculates the energy relaxation time T
1 and the decoherence time T
2 of superconducting qubits is given by solving the set of Bloch-Redfield equations and considering the results of decoherence
of a superconducting charge qubit. Compared to the spin-boson model, it not only contains the decoherence being caused by
the dissipative environment, but also includes the decoherence being generated by the dissipative elements in a superconducting
electronic circuit. Hence, it is good for studying the decoherence of superconducting qubits comprehensively. 相似文献
13.
LI Zeng-Zhao LI Zhi-Qiang 《理论物理通讯》2009,51(2):345-348
In this paper, we investigate the decoherence time of a double quantum dot (DQD) charge qubit in three kinds of baths through solving dynamics of the qubit. The dynamics of the qubit is investigated with Redfield master equation. It is shown that the decoherence time of the qubit in Ohmic bath has the same order of magnitude as the experiments reported. When the environment is modeled with the supra-Ohmic bath the decoherence time of the qubit is shorter than the experimental result. And when modeled with the sub-Ohmic bath the decoherence time of the qubit is longer than the experimental result. 相似文献
14.
By virtue of the canonical quantization method, we present a quantization scheme for a charge qubit based on the superconducting quantum interference device (SQUID), taking the self-inductance of the loop into account. Under reasonable short-time approximation, we study the effect of decoherence in the ohmic case by employing the response function and the norm. It is confirmed that the decoherence time, which depends on the parameters of the circuit components, the coupling strength, and the temperature, can be as low as several picoseconds, so there is enough time to record the information. 相似文献
15.
Y. Shimazu Y. Wada T. Niizeki Y. Yamamoto T. Yoshida Z. Wada T. Yokoyama 《Physica E: Low-dimensional Systems and Nanostructures》2005,29(3-4):679
We measured magnetic flux produced by coupled flux qubits with a switching current measurement of a DC-SQUID. Both the circulating currents and the SQUID–qubit coupling were designed to be asymmetric. The experimental result exhibits a broad peak and dip, and does not agree with the thermally averaged magnetic flux calculated with the two qubit Hamiltonian. This disagreement can be explained in terms of nonthermal excitation of the coupled qubits, which is probably caused by the microwaves generated by the DC-SQUID in the voltage state. 相似文献
16.
Bao-Long Liang Ji-Suo Wang Xiang-Guo Meng Jie Su 《International Journal of Theoretical Physics》2009,48(6):1545-1553
Via the Hamilton dynamical approach we have constructed Hamiltonian for the mutual inductance coupling magnetic flux qubits.
The entangled state representation is used to propose Cooper-pair number-phase quantization and the Hamiltonian operator for
the whole system. The dynamical evolution of the phase difference operator and the Cooper-pairs number operator is investigated
by virtue of Heisenberg equations.
Project 10574060 supported by the National Natural Science Foundation of China and project X071045 supported by the Science
Foundation of Liaocheng University. 相似文献
17.
Fabrication of Al/AlO_x/Al junctions using pre-exposure technique at 30-keV e-beam voltage 下载免费PDF全文
We fabricate high-quality A1/A1O_x/A1 junctions using improved bridge and bridge-free techniques at 30-keV e-beam voltage,in which the length of undercut and the size of junction can be well controlled by the pre-exposure technique.The dose window is 5 times as large as that used in the usual Dolan bridge technique,making this technique much more robust.Similar results,comparable with those achieved using a 100-keV e-beam writer,are obtained,which indicate that the 30-keV e-beam writer could be an economic choice for the superconducting qubit fabrication. 相似文献
18.
19.
In the preparations of superconducting qubits, circuit design is a vital process because the parameters and layout of the circuit not only determine the way we address the qubits, but also strongly affect the qubit coherence properties. One of the most important circuit parameters, which needs to be carefully designed, is the mutual inductance among different parts of a superconducting circuit. In this paper we demonstrate how to design a gap-tunable flux qubit by layout design and inductance extraction using a fast field solver Fast Henry. The energy spectrum of the gap-tunable flux qubit shows that the measured parameters are close to the design values. 相似文献
20.
Fabrication of Al/AlOx/Al Josephson junctions and superconducting quantum circuits by shadow evaporation and a dynamic oxidation process 下载免费PDF全文
Besides serving as promising candidates for realizing quantum computing,superconducting quantum circuits are one of a few macroscopic physical systems in which fundamental quantum phenomena can be directly demonstrated and tested,giving rise to a vast field of intensive research work both theoretically and experimentally.In this paper we report our work on the fabrication of superconducting quantum circuits,starting from its building blocks:Al/AlOx /Al Josephson junctions.By using electron beam lithography patterning and shadow evaporation,we have fabricated aluminum Josephson junctions with a controllable critical current density(jc) and wide range of junction sizes from 0.01 μm2 up to 1 μm2.We have carried out systematical studies on the oxidation process in fabricating Al/AlOx/Al Josephson junctions suitable for superconducting flux qubits.Furthermore,we have also fabricated superconducting quantum circuits such as superconducting flux qubits and charge-flux qubits. 相似文献