采用陶瓷工艺制备了 YBa_2Cu_(3-x)Fe_xO(7-δ)系列样品,其中 x 分别取0.01,0.03,0.060.10,0.20,0.50和1.00。样品的 X 射线衍射图表明 Y-Ba-Cu-Fe 系列样品按 x 含量大致可以划分为三个不同的相结构区。即正交相结构区(x<0.10)、正...采用陶瓷工艺制备了 YBa_2Cu_(3-x)Fe_xO(7-δ)系列样品,其中 x 分别取0.01,0.03,0.060.10,0.20,0.50和1.00。样品的 X 射线衍射图表明 Y-Ba-Cu-Fe 系列样品按 x 含量大致可以划分为三个不同的相结构区。即正交相结构区(x<0.10)、正交和四方混合的相结构区(0.10≤x<1.00),四方相结构区(x≥1.00)。展开更多
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 demonstrat...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.展开更多
Highly epitaxial YBa2Cu3O7-δ （YBCO） and yttria-stabilized zirconia （YSZ） bilayer thin films have been deposited on silicon-on-insulator （SOI） substrates by using in situ pulsed laser deposition （PLD） techniqu...Highly epitaxial YBa2Cu3O7-δ （YBCO） and yttria-stabilized zirconia （YSZ） bilayer thin films have been deposited on silicon-on-insulator （SOI） substrates by using in situ pulsed laser deposition （PLD） technique. In the experiment, the native amorphous SiO2 layers on some of the SOI substrates are removed by dipping them in a 10% HF solution for 15 s. Comparing several qualities of films grown on substrates with or without HF pretreatment, such as thin film crystallinity, general surface roughness, temperature dependence of resistance, surface morphology, as well as average crack spacing and crack width, naturally leads to the conclusion that preserving the native SiO2 layer on the surface of the SOI substrate can not only simplify the experimental process but can also achieve fairly high quality YSZ and YBCO thin films.展开更多
This paper reports the fabrication and test of a high-Tc SQUID planar gradiometer which is patterned from YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77K shows that t...This paper reports the fabrication and test of a high-Tc SQUID planar gradiometer which is patterned from YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77K shows that the white noise at 200 Hz is about 1×10^-4 φ0/√Hz. The minimal magnetic gradient is measured and the results suggest that the minimal magnetic gradient is 94 pT/m. The planar gradiometer is used in non-destructive evaluation （NDE） experiments to detect the artifacts in conducting aluminium plates by performing eddy current testing in an unshielded environment. The effect of the exciting coil dimension on the NDE results is investigated. By mapping out the induced field distribution, flaws about 10mm below the plate surface can be clearly identified.展开更多
We carry out an ultra-low-field nuclear magnetic resonance （NMR） experiment based on high-T c superconducting quantum interference devices （SQUIDs）. The measurement field is in a micro-tesla range （～10 μT-100 ...We carry out an ultra-low-field nuclear magnetic resonance （NMR） experiment based on high-T c superconducting quantum interference devices （SQUIDs）. The measurement field is in a micro-tesla range （～10 μT-100 μT） and the experiment is conducted in a home-made magnetically-shielded-room （MSR）. The measurements are performed by the indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using the SQUID with that achieved using a conventional low-noise-amplifier, we perform the measurements using a commercial room temperature amplifier. The results show that in a wide frequency range （～1 kHz-10 kHz） the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity as the measurement field increases. This is verified by compensating the field gradient using three sets of gradient coils.展开更多
We study two flux qubits with a parameter coupling scenario. Under the rotating wave approximation, we truncate the 4-dimensional Hilbert space of a coupling flux qubits system to a 2-dimensional subspace spanned by t...We study two flux qubits with a parameter coupling scenario. Under the rotating wave approximation, we truncate the 4-dimensional Hilbert space of a coupling flux qubits system to a 2-dimensional subspace spanned by two dressed states ｜01} and ｜10}. In this subspace, we illustrate how to generate an Aharnov Anandan phase, based on which, we can construct a NOT gate （as effective as a C-NOT gate） in this coupling flux qubits system. FinMly, the fidelity of the NOT gate is also calculated in the presence of the simulated classical noise.展开更多
The reoccurrence of pits has been found on the surfaces of c-axis YBa2CusO7-δ(YBCO)films grown epitaxially on 10℃vicinal SrTiOs substrates by pulsed laser deposition.They are always associated with films with a step...The reoccurrence of pits has been found on the surfaces of c-axis YBa2CusO7-δ(YBCO)films grown epitaxially on 10℃vicinal SrTiOs substrates by pulsed laser deposition.They are always associated with films with a stepterrace structure,while polycrystalline films have no pits.Pit formation is attributed to the large interfacial stress induced by vicinal substrate and oxygen deficiency of the YBCO film during the tetragonal-to-orthorhombic(TO)phase transition,which cannot be released by forming twins,and leads to rupturing of the film surface.By reducing the oxidation partial pressure for the T-O phase transition to 80 Pa,no pits were formed,and the YBCO film is superconducting at 60K.展开更多
Josephson effects have been observed in Nb/YBa_(2)Cu_(3)O_(7-δ) point contacts and YBa_(2)Cu_(3)O_(7-δ) break junctions.When the junctions are exposed to a microwave field,the I-V characteristics show constant volta...Josephson effects have been observed in Nb/YBa_(2)Cu_(3)O_(7-δ) point contacts and YBa_(2)Cu_(3)O_(7-δ) break junctions.When the junctions are exposed to a microwave field,the I-V characteristics show constant voltage steps,the heights of which follow the Bessel function behavior.Obvious asymmetry about zero bias has been observed in YBCO break junctions which,we suggest,may possibly result from flux trapping in the complicated weak link structure of the system.Micrmave-induced sub-steps have also been found in YBCO break junctions.All experiments were conducted at liquid helium temperature.展开更多
Point-contact tunneling measurements of the oxide superconductor Y-Ba-Cu-O were carried out with both Nb and Mo tips.An energy gap,Δ=18.5meV and 2Δ/kT_(c)=4.7 were obtained.The result is consistent with the strong-c...Point-contact tunneling measurements of the oxide superconductor Y-Ba-Cu-O were carried out with both Nb and Mo tips.An energy gap,Δ=18.5meV and 2Δ/kT_(c)=4.7 were obtained.The result is consistent with the strong-coupling theory.The tunneling conductance curves indicate a granular feature of the sample.展开更多
文摘采用陶瓷工艺制备了 YBa_2Cu_(3-x)Fe_xO(7-δ)系列样品,其中 x 分别取0.01,0.03,0.060.10,0.20,0.50和1.00。样品的 X 射线衍射图表明 Y-Ba-Cu-Fe 系列样品按 x 含量大致可以划分为三个不同的相结构区。即正交相结构区(x<0.10)、正交和四方混合的相结构区(0.10≤x<1.00),四方相结构区(x≥1.00)。
基金supported by the Science Foundation of the Ministry of Science and Technology of China (Grant Nos. 2011CBA00106 and 2009CB929102)the National Natural Science Foundation of China (Grant Nos. 11104333,10974243,and 11161130519)the Knowledge Innovation Program of the Chinese Academy of Sciences
文摘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.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 50672125 and 10574154)the Natural Science Foundation of Shanxi Province, China (Grant No 2009011003-1)the Youth Foundation of Shanxi Datong University, China (Grant No 2007Q10)
文摘Highly epitaxial YBa2Cu3O7-δ （YBCO） and yttria-stabilized zirconia （YSZ） bilayer thin films have been deposited on silicon-on-insulator （SOI） substrates by using in situ pulsed laser deposition （PLD） technique. In the experiment, the native amorphous SiO2 layers on some of the SOI substrates are removed by dipping them in a 10% HF solution for 15 s. Comparing several qualities of films grown on substrates with or without HF pretreatment, such as thin film crystallinity, general surface roughness, temperature dependence of resistance, surface morphology, as well as average crack spacing and crack width, naturally leads to the conclusion that preserving the native SiO2 layer on the surface of the SOI substrate can not only simplify the experimental process but can also achieve fairly high quality YSZ and YBCO thin films.
基金Project supported by Ministry of Science and Technology of China （Grant Nos 2006CB601007 and 2002AA306412 ）, National Nature Science Foundation of China （Grant No 10221002） and Chinese Academy of Sciences and National Center for Nanoscience and Technology, China.
文摘This paper reports the fabrication and test of a high-Tc SQUID planar gradiometer which is patterned from YBCO thin film deposited on a SrTiO3 bicrystal substrate. The measurement of noise spectrum at 77K shows that the white noise at 200 Hz is about 1×10^-4 φ0/√Hz. The minimal magnetic gradient is measured and the results suggest that the minimal magnetic gradient is 94 pT/m. The planar gradiometer is used in non-destructive evaluation （NDE） experiments to detect the artifacts in conducting aluminium plates by performing eddy current testing in an unshielded environment. The effect of the exciting coil dimension on the NDE results is investigated. By mapping out the induced field distribution, flaws about 10mm below the plate surface can be clearly identified.
基金Project supported by the State Key Development Program for Basic Research of China (Grant Nos. 2011CBA00106 and 2009CB929102)the National Natural Science Foundation of China (Grant Nos. 11104333, 11161130519, and 10974243)
文摘We carry out an ultra-low-field nuclear magnetic resonance （NMR） experiment based on high-T c superconducting quantum interference devices （SQUIDs）. The measurement field is in a micro-tesla range （～10 μT-100 μT） and the experiment is conducted in a home-made magnetically-shielded-room （MSR）. The measurements are performed by the indirect coupling method in which the signal of nuclei precession is indirectly coupled to the SQUID through a tuned copper coil transformer. In such an arrangement, the interferences of applied measurement and polarization field to the SQUID sensor are avoided and the performance of the SQUID is not destroyed. In order to compare the detection sensitivity obtained by using the SQUID with that achieved using a conventional low-noise-amplifier, we perform the measurements using a commercial room temperature amplifier. The results show that in a wide frequency range （～1 kHz-10 kHz） the measurements with the SQUID sensor exhibit a higher signal-to-noise ratio. Further, we discuss the dependence of NMR peak magnitude on measurement frequency. We attribute the reduction of the peak magnitude at high frequency to the increased field inhomogeneity as the measurement field increases. This is verified by compensating the field gradient using three sets of gradient coils.
基金Project supported by the National Basic Research Program of China (Grant Nos. 2011CBA00106 and 2009CB929102)the National Natural Science Foundation of China (Grant Nos. 11161130519 and 10974243)the Fundamental Research Funds for the Central Universities, China (Grant No. CDJXS11100012)
文摘We study two flux qubits with a parameter coupling scenario. Under the rotating wave approximation, we truncate the 4-dimensional Hilbert space of a coupling flux qubits system to a 2-dimensional subspace spanned by two dressed states ｜01} and ｜10}. In this subspace, we illustrate how to generate an Aharnov Anandan phase, based on which, we can construct a NOT gate （as effective as a C-NOT gate） in this coupling flux qubits system. FinMly, the fidelity of the NOT gate is also calculated in the presence of the simulated classical noise.
基金Supported by the National Natural Science Foundation of China under Grant No.59392800the National Center for Research&Development on Superconductivity of China.
文摘The reoccurrence of pits has been found on the surfaces of c-axis YBa2CusO7-δ(YBCO)films grown epitaxially on 10℃vicinal SrTiOs substrates by pulsed laser deposition.They are always associated with films with a stepterrace structure,while polycrystalline films have no pits.Pit formation is attributed to the large interfacial stress induced by vicinal substrate and oxygen deficiency of the YBCO film during the tetragonal-to-orthorhombic(TO)phase transition,which cannot be released by forming twins,and leads to rupturing of the film surface.By reducing the oxidation partial pressure for the T-O phase transition to 80 Pa,no pits were formed,and the YBCO film is superconducting at 60K.
文摘Josephson effects have been observed in Nb/YBa_(2)Cu_(3)O_(7-δ) point contacts and YBa_(2)Cu_(3)O_(7-δ) break junctions.When the junctions are exposed to a microwave field,the I-V characteristics show constant voltage steps,the heights of which follow the Bessel function behavior.Obvious asymmetry about zero bias has been observed in YBCO break junctions which,we suggest,may possibly result from flux trapping in the complicated weak link structure of the system.Micrmave-induced sub-steps have also been found in YBCO break junctions.All experiments were conducted at liquid helium temperature.
文摘Point-contact tunneling measurements of the oxide superconductor Y-Ba-Cu-O were carried out with both Nb and Mo tips.An energy gap,Δ=18.5meV and 2Δ/kT_(c)=4.7 were obtained.The result is consistent with the strong-coupling theory.The tunneling conductance curves indicate a granular feature of the sample.
