dc SQUID amplifiers for readout of quantum bits

dc SQUID amplifiers for readout of quantum bits a

abc

T. Miyazaki , T. Yamamoto , Y. Nakamuraabc, S. Yorozuab, M. Hidakaad abc and J. S. Tsai a) CREST, Japan Science and Technology Agency b) Nano Electronics Research Laboratories, NEC Corp., Japan c) Frontier Research System, RIKEN, Japan d) International Superconductivity Technology Center, Japan

An example of qubit readout scheme ●

Signal frequency is several GHz. –

Sufficiently higher than bath temperature of a dilution refrigerator (~ 10 mK)

–

S/N is limited by the amplifier noise temperature (~5 K). → Requires average measurement ~10 mK

1 ~ 4 . 2K

300K ATT

ATT

ATT

BPF

Qubit chip

Circulator

Microwave source Circulator Measurement 50Ω Microwave amp . T N ~ 5 K, P ~ 50 mW

BPF

M Qubit

We propose to... ●

Add dc-SQUID amplifier (SQA). –

Low noise temperature (< 1K)

–

Very low power consumption

→ Single-shot and non-demolition readout ~10 mK

1 ~ 4 . 2K

300K ATT

ATT

ATT

BPF

Qubit chip

Circulator

Microwave source Circulator

BPF

M Qubit

Measurement 50Ω Microwave amp . T N ~ 5 K, P ~ 50 mW

SQUID amp . G ~10dB T N ~ 0 . 5 K, P < 100 nW

dc SQUID amplifier for microwave ●

Hilbert and Clarke –

[1]

Add Cin to resonate.

Iin

Resonance 0~1/  L in C in 2 ● Input impedance Rin~k 0 L in

Cin

Ibias k

Lin

●

●

Prokopenko et al. – fc –

[2]

= 4 GHz, Δf-3dB=300 MHz

Gain~10 dB, Noise temperature~0.5 K (quantum limit ~ 0.2 K @ 4GHz)

Vout

Target specifications ●

Signal frequency fc~10 GHz Qubit fabrication and measurement is set up for ~ 10 GHz

●

Gain > 10 dB Effective noise temperature of the semiconductor amplifier becomes < 1/10

●

●

Noise temperature close to the quantum limit (~0.5 K at 10 GHz) Low power consumption (< 1 μW)

Design of SQA (1) ●

Basic parameters – Ic=20

μA per junction (40 μA for a SQUID)

–

Chip size 2.5 mm×2.5 mm < λ (~ 12mm)

–

⇒ Lumped element approach design |Zin| 10 dB

–

Δf-3dB ~ 340 MHz

–

1 dB compression point -80 dBm

Ic [μA] fc [GHz] Δf [GHz] Gmax [dB]

Simulation 40.0 10.0 1.1 9.6

Wafer #1 35.0 9.41 0.34 12.6

Summary ●

Designed and fabricated dc-SQUID amplifier for 10 GHz signal. –

Achieved > 10 dB gain at 9.4 GHz.

–

2 chips from different wafers showed good agreement.

–

Bandwidth is less than half of the simulation.

Plans ●

Evaluate more SQAs. –

●

We have evaluated 1 design, 3 others are waiting for measurement.

Do noise temperature measurement. –

At 4.2 K and lower

●

Apply to qubit readout.

●

Optimize design.

References and Acknowledgment [1] C. Hilbert and J. Clarke, J. of Low Temp. Phys. 61 263 (1985). [2] G.V.Prokopenko et. al., IEEE Trans. Appl. Supercond. 15 741 (2005) [3] M.B.Ketchen, IEEE Trans. on Magn. MAG-23 1650 (1987). [4] J.Beyer et. al., International Workshop on Low Temperature Detectors (LTD-11), (2005) Some part of this work use the result of NEDO's “Superconducting network device” project. We thank M. Maezawa, S. Kohjiro, R.W. Simmonds, G.V. Prokopenko and Y. Hashimoto for useful discussions. We also thank M. Isaka for fabrication of chips.