We propose a relaxation rate or dissipative cavity-based parameters that can be used as indicators of the stationary limit of a mixed state geometric phase. We perform our considerations for the system of a supercondu...We propose a relaxation rate or dissipative cavity-based parameters that can be used as indicators of the stationary limit of a mixed state geometric phase. We perform our considerations for the system of a superconducting qubit in an open transmission line or interacting with a dissipative cavity. This system is very useful for performing an effective quantum computation by exhibiting the long collapse time of the geometric phase. It is shown that the geometric phase in the stationary limit does not depend on interaction time if the decay time exceeds an upper bound.展开更多
We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device（SQUID） detector are prepared by shadow evaporatio...We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device（SQUID） detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm^2 are fabricated for the qubit, in which the number of the decoherencecausing two-level systems（TLS） residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T1 and dephasing time Tφ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.展开更多
We propose a simple scheme to generate x-type four-charge entangled states by using SQUID-based charge qubits capacitively coupled to a transmission line resonator （TLR）. The coupling between the superconducting qub...We propose a simple scheme to generate x-type four-charge entangled states by using SQUID-based charge qubits capacitively coupled to a transmission line resonator （TLR）. The coupling between the superconducting qubit and the TLR can be effectively controlled by properly adjusting the control parameters of the charge qubit. The experimental feasibility of our scheme is also shown.展开更多
We propose a scheme for generating Bell states involving two SQUID-based charge qubits by coupling themto a nanomechanical resonator.We also show that it is possible to implement a two-qubit logic gate between the two...We propose a scheme for generating Bell states involving two SQUID-based charge qubits by coupling themto a nanomechanical resonator.We also show that it is possible to implement a two-qubit logic gate between the twocharge qubits by choosing carefully the interaction time.展开更多
Realization of a flexible and tunable coupling scheme among qubits is critical for scalable quantum information processing.Here,we design and characterize a tunable coupling element based on Josephson junction,which c...Realization of a flexible and tunable coupling scheme among qubits is critical for scalable quantum information processing.Here,we design and characterize a tunable coupling element based on Josephson junction,which can be adapted to an all-to-all connected circuit architecture where multiple Xmon qubits couple to a common coplanar waveguide resonator.The coupling strength is experimentally verified to be adjustable from 0 MHz to about 40 MHz,and the qubit lifetime can still be up to 12μs in the presence of the coupling element.展开更多
The influence of intrinsic decoherence on various correlations and dense coding in a model which consists of two identical superconducting charge qubits coupled by a fixed capacitor is investigated. The results show t...The influence of intrinsic decoherence on various correlations and dense coding in a model which consists of two identical superconducting charge qubits coupled by a fixed capacitor is investigated. The results show that, despite the intrinsic decoherence, the correlations as well as the dense coding channel capacity can be effectively increased via the combination of system parameters, i.e., the mutual coupling energy between the two charge qubits is larger than the Josephson energy of the qubit. The bigger the difference between them is, the better the effect is.展开更多
We investigate the entropy squeezing in the system of a superconducting charge qubit coupled to a singlemode field.We find an exact solution of the Milburn equation for the system and discuss the influence of intrinsi...We investigate the entropy squeezing in the system of a superconducting charge qubit coupled to a singlemode field.We find an exact solution of the Milburn equation for the system and discuss the influence of intrinsicdecoherence on entropy squeezing.As a comparison,we also consider the variance squeezing.Our results show that inthe 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 timegoing on the entropy squeezing disappears fast than the variance squeezing,there exists a range of time where entropysqueezing can occur but variance squeezing cannot.展开更多
The Hamiltonian of a superconducting charge qubit with a configuration of dc SQUID contains an interac-tion between the LC oscillator part and charge qubit.This interaction may leads to quantum state collapse and revi...The Hamiltonian of a superconducting charge qubit with a configuration of dc SQUID contains an interac-tion between the LC oscillator part and charge qubit.This interaction may leads to quantum state collapse and revivalwhich degrades the charge qubits and leads to serious decoherence.An analysis shows that the existing charge qubitparameters do not lead to this phenomenon,which is very good for the superconducting charge展开更多
We demonstrate the effect of different coupling strengths between a microscopic two-level system(TLS)and a microwave field on the dynamics of a qubit—TLS system when the bipartite system is subject to resonant microw...We demonstrate the effect of different coupling strengths between a microscopic two-level system(TLS)and a microwave field on the dynamics of a qubit—TLS system when the bipartite system is subject to resonant microwave driving.Rabi beating with a different TLSmicrowave coupling strength is demonstrated in simulations.Entanglement,quantified by the concurrence between the qubit and TLS,both for pure states and mixed states,is simulated.When decoherence is considered,entanglement of the bipartite system oscillates with damping and exhibits entanglement sudden death and/or entanglement sudden death and revival.展开更多
文摘We propose a relaxation rate or dissipative cavity-based parameters that can be used as indicators of the stationary limit of a mixed state geometric phase. We perform our considerations for the system of a superconducting qubit in an open transmission line or interacting with a dissipative cavity. This system is very useful for performing an effective quantum computation by exhibiting the long collapse time of the geometric phase. It is shown that the geometric phase in the stationary limit does not depend on interaction time if the decay time exceeds an upper bound.
基金supported by the National Basic Research Program of China(Grant Nos.2014CB921202,2015CB921104,and 2016YFA0300601)the National Natural Science Foundation of China(Grant Nos.91321208 and 11674380)
文摘We develop a fabrication process for the superconducting phase qubits in which Josephson junctions for both the qubit and superconducting quantum interference device（SQUID） detector are prepared by shadow evaporation with a suspended bridge. Al junctions with areas as small as 0.05 μm^2 are fabricated for the qubit, in which the number of the decoherencecausing two-level systems（TLS） residing in the tunnel barrier and proportional to the junction area are greatly reduced. The measured energy spectrum shows no avoided crossing arising from coherent TLS in the experimentally reachable flux bias range of the phase qubit, which demonstrates the energy relaxation time T1 and dephasing time Tφ on the order of 100 ns and 50 ns, respectively. We discuss several possible origins of decoherence from incoherent or weakly-coupled coherent TLS and further improvements of the qubit performance.
基金supported by the National Natural Science Foundations of China (Grant Nos. 10947017/A05 and 11074190)the Science Foundation of the Key Laboratory of Novel Thin Film Solar Cells, China (Grant No. KF200912)the Graduates' Innovative Scientific Research Project of Zhejiang Province, China (Grant No. 2011831)
文摘We propose a simple scheme to generate x-type four-charge entangled states by using SQUID-based charge qubits capacitively coupled to a transmission line resonator （TLR）. The coupling between the superconducting qubit and the TLR can be effectively controlled by properly adjusting the control parameters of the charge qubit. The experimental feasibility of our scheme is also shown.
基金The project supported by National Natural Science Foundation of China under Grant No. 10325523the National Fundamental Research Program of China under Grant No. 2001CB309310the Scientific Research Fund of the Education Department of Hunan Province under Grant No. 06C354
文摘We propose a scheme for generating Bell states involving two SQUID-based charge qubits by coupling themto a nanomechanical resonator.We also show that it is possible to implement a two-qubit logic gate between the twocharge qubits by choosing carefully the interaction time.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2017YFA0304300 and 2016YFA0300600)the National Natural Science Foundation of China(Grant Nos.11725419 and 11434008)the Strategic Priority Research Program of Chinese Academy of Sciences(Grant No.XDB28000000)
文摘Realization of a flexible and tunable coupling scheme among qubits is critical for scalable quantum information processing.Here,we design and characterize a tunable coupling element based on Josephson junction,which can be adapted to an all-to-all connected circuit architecture where multiple Xmon qubits couple to a common coplanar waveguide resonator.The coupling strength is experimentally verified to be adjustable from 0 MHz to about 40 MHz,and the qubit lifetime can still be up to 12μs in the presence of the coupling element.
基金Project supported by the Project to Develop Outstanding Young Scientific Talents of China(Grant No.2013711019)the Natural Science Foundation of Xinjiang Province,China(Grant No.2012211A052)+1 种基金the Foundation for Key Program of Ministry of Education of China(Grant No.212193)the Innovative Foundation for Graduate Students Granted by the Key Subjects of Theoretical Physics of Xinjiang Province,China(Grant No.LLWLL201301)
文摘The influence of intrinsic decoherence on various correlations and dense coding in a model which consists of two identical superconducting charge qubits coupled by a fixed capacitor is investigated. The results show that, despite the intrinsic decoherence, the correlations as well as the dense coding channel capacity can be effectively increased via the combination of system parameters, i.e., the mutual coupling energy between the two charge qubits is larger than the Josephson energy of the qubit. The bigger the difference between them is, the better the effect is.
基金National Natural Science Foundation of China under Grant Nos.10374007 and 60472021
文摘We investigate the entropy squeezing in the system of a superconducting charge qubit coupled to a singlemode field.We find an exact solution of the Milburn equation for the system and discuss the influence of intrinsicdecoherence on entropy squeezing.As a comparison,we also consider the variance squeezing.Our results show that inthe 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 timegoing on the entropy squeezing disappears fast than the variance squeezing,there exists a range of time where entropysqueezing can occur but variance squeezing cannot.
基金The project supported by the 973 Program under Grant No.2006CB921106National Natural Science Foundation of China under Grant Nos.10325521,60433050,60635040the SRFDP Program of Education Ministry of China under Grant No.20060003048
文摘The Hamiltonian of a superconducting charge qubit with a configuration of dc SQUID contains an interac-tion between the LC oscillator part and charge qubit.This interaction may leads to quantum state collapse and revivalwhich degrades the charge qubits and leads to serious decoherence.An analysis shows that the existing charge qubitparameters do not lead to this phenomenon,which is very good for the superconducting charge
基金supported by the National Basic Research Program of China (2011CBA00107 and 2011CBA00202)the National Natural Science Foundation of China (61371036,11074114 and 11227904)+1 种基金the Natural Science Foundation of Jiangsu (BK2012013)the CAEP THz Science and Technology Foundation (CAEPTHZ201206)
文摘We demonstrate the effect of different coupling strengths between a microscopic two-level system(TLS)and a microwave field on the dynamics of a qubit—TLS system when the bipartite system is subject to resonant microwave driving.Rabi beating with a different TLSmicrowave coupling strength is demonstrated in simulations.Entanglement,quantified by the concurrence between the qubit and TLS,both for pure states and mixed states,is simulated.When decoherence is considered,entanglement of the bipartite system oscillates with damping and exhibits entanglement sudden death and/or entanglement sudden death and revival.
