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1、超导量子比特的测量于 扬南京大学物理系量子输运实验讲习班物理所 , 2006/12/201. 超导量子比特基础S SJosephson Junction and EquationsIs = Icsind/dt = 2eV/hSuperconducting qubitsPhase qubit:Flux qubit:Charge qubit:1|0|1|0|1|0|11.2 Phase qubit2 12 ( 1 cos )JU E i i iEscape1/ exp( / )2 pth t Ba U k T1/27.2120 exp 7.22n nPQp pU Uesc th Q2. 超导相位比
2、特的频域测量IbVTIME测量示意MicrowaveSourcet1 t2IWave generatorSyn. OutputTimert1 t2PCtesc = t2t1tescOptocouplerVPre-ampEMIfilters1 K potRCfiltersMixingchamber-wavefilters4.2 KMu-metalshield20dBattenuatorDCblock300 KMu-metalshieldJJOFC shieldSwitching distribution( )escN dt P I dI30025020015010050035.7035.6535
3、.6035.5535.5035.4535.40Dist to rate0( ) 1( ) exp ( )/ /IescescIP I i didI dt dI dt100101102103104(1/s)100806040200U (K)0( ) /( )1 ( )esc IP I dI dtIP i di( )escN dt P I dISpectroscopy30025020015010050035.7035.6535.6035.5535.5035.4535.4010210310410510635.7035.6535.6035.5535.5035.45Ib 不定 !3. 超导量子比特的时域
4、测量1. 自由演化2. 两态测试3.1 自由演化测量数据escdN N dt1 esctescN e测量举例PotentialEnergyw101010|0|1|211030Microwave420-2-4Time (ms)dc bias currentMicrowave currentjunction0Rabi Oscillation0.300.250.200.150.100.050.00P(s-1)20151050Time (s)200010000P(a.u.)2.01.51.00.50.0Time (s)Far off-resonance-18.900.01Mrad/s4.910.03s
5、眪眪Yu et al. Science296, 8893.2 两态测试 PC qubit的 测量Superconducting persistent current (PC) qubitsT. P. Orlando et. al. PRB 1999BJJ1 JJ2JJ3IpQuantum two level system0 1Ux =0/2 2F=(2x-0)IpUIpEFNb PC qubit5mDC SQUIDPC qubitDC SQUIDPC qubitI+I-V+V-Readout qubit statesT =x +qubitIIRswVVgILsw43210 -2 -1 0 1
6、22.42.22.01.8-0.64 -0.62 -0.60 -0.58Frustration (0)Switchingcurrent(A)microwaveSQUID bias currentSQUID voltageMeasurement TimingtpultdelayFlux bias要求1. tdelay小于消相干时间2. 耦合到 QUBIT的噪声小3. 电压信号的放大1. 同轴电缆2. 衰减器3. 低温或室温放大器测量装置示意图衰减器衰减器隔直器 微波过滤器RC过滤器Spectroscopy (2D)Resonant peaks at= 3.25 GHzIbEFSpectrosco
7、py (1D)Resonant peaks at= 3.25 GHz-10 -5 0 5Magnetic flux (m0)SwitchingProbabilityEF01Resonant Peaks at 10 GHz1.00.50.0Magnetic Flux (m0)0 5 10-5-10SwitchingProbabilityFrequency vs Peak Position20151050Frequency(GHz)2520151050Frustration (mF0)Magnetic Flux (m0)403020100-10Frequency(GHz)-15 -10 -5 0
8、5 10 15Flux from degeneracy (m0)Energy diagram1.00.50.010 GHz0.40.20.0Population4003002001000Delay Time (ms)Energy relaxation timeT1 30stdelayYang Yu et al. PRL 2004(d)46W38W60W20151050RabiFrequency(MHz)0.40.20.0POWER( mW)(b)(c)(a) (e)0.40.20.0Population9.939.919.89Frequency (GHZ)0.60.40.20.00.60.40.20.00.60.40.20.0 4003002001000Rabi Pulse Time (ns)3-photon Rabi oscillationstpulrabi 50 ns
