Resonant Peaks at 10 GHz
1.0
Switching Probability
0.5 0.0
-10
-5 0 5 Magnetic Flux (m0)
10
Frequency vs Peak Position
20
Frequency (GHz)
15
10
5
0 0 5 10 15 20 FrustrationFlux (m<??>F 0) ) Magnetic (m
10
3
(1/s)
10
2
10
1
10
0
0
20
40
U (K)
60
80
100
Spectroscopy
300 250 200
Ib 不定!!!
150
100
50
0 35.40
35.45
35.50
35.55
35.60
35.65
35.70
10
6
10
5
10
4
10
3
10
2
35.45

35.55
35.60
35.65
隔直器 微波过滤器
Spectroscopy (2D)
Resonant peaks at = 3.25 GHz
Ib
E
F
Spectroscopy (1D)
Resonant peaks at = 3.25 GHz
1
E F
Switching Probability
0
-10
-5
0
5
Magnetic flux (m0)
Flux bias
tpul
microwave
tdelay
SQUID bias current
SQUID voltage
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
RC过滤器
衰减器
|0
|1
Flux qubit:
|0
1
|1
Charge qubit:
|0
|1
1.2 Phase qubit
U 2EJ ( 1 i 2 i cos1 i)
Escape p th 1/ at exp( U / k BT ) 2
7.2U n Q 120 p P U n exp 7.2 2 p
1/2
esc th Q
2. 超导相位比特的频域测量
Ib
V TIME
Wave generator
Timer
Opto coupler
测量示意
tesc t2
Syn.
Output
t1
PC tesc = t2 t1
V Pre-amp Microwave Source t1 t2 I
EMI filters
JJ3
Ip B
JJ1 JJ2
T. P. Orlando et. al. PRB 1999
Quantum two level system
U Ip U
0
x = 0/2
1
2F=(2x-0)Ip

E

F
Nb PC qubit
I+
DC SQUID
V+
DC SQUID PC qubit
PC qubit
300
250
200
150
100
50
0 35.40
35.45
35.50
35.55
35.60
35.65
35.70
Dist to rate
N esc dt P( I ) dI
esc ( I ) P ( I ) dI / dt 1 P (i ) di
0 I
10
4
I esc ( I ) 1 P( I ) exp ( i ) di esc dI / dt dI / dt 0
0
25
Energy diagram
1.0
10 GHz
0.5 0.0
Frequency (GHz)
40 30 20 10 0 -10 -15 -10 10 Flux from degeneracy (m0) -5 0 5 15
Energy relaxation time
300 K
4.2 K
Mumetal shield
RC filters
1 K pot
20dB
attenuator
-wave filters
Mixing chamber
DC block
JJ
OFC shield
Mumetal shield
Switching distribution
N esc dt P( I ) dI
5m
I-
V-
Readout qubit states
2.4 2.2 2.0 1.8
4
-0.64 -0.62 -0.60 -0.58
T = x + qubit
I
IRsw ILsw
Switching current (A)
3 2 1 0
Vg
V
-2
-1
0
1
2
Frustration (0)
Measurement Timing
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, 2006/12/20
1. 超导量子比特基础
Josephson Junction and Equations
S
S
Is = Icsin d/dt = 2eV/h
Superconducting qubits
Phase qubit:
0.20
P (s )
-1
0 0.15
0.0
0.5
Time ( s)
1.0
1.5
2.0
0.10
8.900.01Mrad/s 眪
0.05
眪4.910.03s
-1
0.00 0 5
Time ( s)
10
15
20
3.2 两态测试—PC qubit的测量
Superconducting persistent current (PC) qubits

dc bias current Microwave current junction voltage
0
-4
-2
0
2
4
Time (ms)
Rabi Oscillation
0.30
P (a.u.)
0.25
Yu et al. Science 296, 889
2000
Far off-resonance
1000
35.70
3. 超导量子比特的时域测量
1. 自由演化 2. 两态测试
3.1 自由演化
测量数据
dN N esc dt
Nesc 1 e
esc t
测量举例
Potential Energy
|2 |1
w Microwave

10
1 1030

10
1
|0
0