Superconducting Quantum ComputingXiaobo Zhu

CAS Center for Excellence in Quantum Information and Quantum Physics

University of Science and Technology of China

ITU Workshop on Quantum Information Technology (QIT) for Networks

Shanghai, China, 5th June 2019

Email: xbzhu16@ustc.edu.cn

How to scale up?

Ultra-high precision analog circuit

• Better pulse calibration

• Less crosstalk

• Less state leakage

• Higher readout efficiency

• Less TLS

• Deeper connectivity

……

More qubits and longer depth

Sample Fabrication

To stabilize the sample parameters

To speed up the development of new samples

Qubit Samples

Longer

Coherent time

3 Bits 5 Bits 6 Bits 9 Bits 10 Bits 12 Bits 24 Bits

T1: ~40usT1: ~5us T1: ~15us

More

Qubits

Ultra-low noise and temperature platform

~100 Coaxial cables

>99.9% voltage resolution

Sample rate>1GHz

Bandwidth ：0-20GHz

~100 DA Chanel

< 20mK

~10ppm(1h) DC bias

Multi-qubit control

▪High-precision controlling of amplitude, phase and time sequence▪Compensation of the crosstalk and calibration of the wave deformation▪Arbitrary multi-channel quantum circuit

Quantum operating System

12-Qubit sample characterizations

Summary of T1 and T2

q1 q2 q3 q4 q5 q6 q7 q8 q9 q10 q11 q12

T1(us) 40.1 34.7 30.8 40.4 31.8 34.3 46.5 38.1 32.2 54.6 29.6 30.3

T2(us) 7.9 1.5 6.3 2.4 4.9 2.7 6.8 2.3 5.1 3.5 5.9 3

f01

(GHz)4.978 4.183 5.192 4.352 5.11 4.226 5.03 4.3 5.142 4.14 4.996 4.26

f_ah

(MHz)-247.7 -203.5 -245.7 -202.7 -246.9 -201.5 -245.8 -203 -243.5 -203.4 -246.4 -201.4

T1 ~ 30us-50us

T2* > 20us at optimal point

Q7 at optimal point Q7 at optimal point

Q7 at optimal point

Q7 at optimal point

Single − qubit gate𝑠 fidelity>99.9%(by randomized benchmarking)

The fidelity of single-qubit gates operation

Nonadiabatic CZ gate

Theoretic simulation

PRL,115, 190801 (2015).

PRX, 8, 021059 (2018).

Leakage from Eigenstate

F>99.97%(After 12 hours

differential evolution (DE)

searching.)

1.06Ts (34ns)for infinite

bandwidth, Ts=1/(2g11,02)

1.17Ts for 300MHz bandwidth

(After 1 hour Nelder Mead (NM)

algorithm searching.)

Experimental results：optimization by RB

The fidelity of CZ gates operation

CZ ~99.54%, After 4 hour NM algorithm searching

12-Qubit Linear Cluster state

Ts =1/(2g11,20)~32ns

g11,20=15.6MHz

Tgate=40ns~1.25Ts

~32ns

CCZ gate

CCZ gate fidelity

F=93.3%(experiment),78.5ns and F=99.3%(numeric)

Conclusion of nonadiabatic way

“Realization of high-fidelity nonadiabatic CZ gates

with superconducting qubits”, submitted

Leakage error in our nonadiabatic CZ gates

is not a major challenge

This scheme is suitable for the design of

CCZ gates ,but a new RB method is needed

NM is sensitivity to initial points

12-Qubit entanglement

Genuine multipartite entanglement (GME)

• Cannot be expressed as a bi-separable state or a mixture of bi-separable states

• Benchmark for the quality of quantum processor

• Greenberger-Horne-Zeilinger (GHZ) state: 𝐺𝐻𝑍N = ( 0 ⊗𝑁 + 1 ⊗𝑁)/ 2

14-qubit GHZ in ion trap

10-qubit GHZ in superconducting

quantum circuit 18-qubit GHZ with six photons

Phys. Rev. Lett. 106, 130506 (2011) Phys. Rev. Lett. 119, 180511 (2017) Phys. Rev. Lett. 120, 260502 (2018)

…

12-Qubit Linear Cluster state

Gate sequence

12-Qubit Linear Cluster state

Parallel optimization of CZ gates

12-Qubit Linear Cluster state

Gate fidelity

State preparation error

Readout error

Triple the length, more ZZ coupling

12-Qubit Linear Cluster state

*Phys. Rev. Lett. 94,

060501 (2005)

Phys. Rep. 474, 1

(2009)

Only two local measurement settings*

12-Qubit Linear Cluster state

LC state fidelity

Over 55% for 12-qubit LC state,

21 statistical standard deviations

above 50%

250,000 projective measurements

12-Qubit Linear Cluster state

12-Qubit Linear Cluster state

0.707(8)

12 − qubit linear cluster state created by single-qubit gates and CZ gates. The fidelity is 70.7±0.8%.

Phys. Rev. Lett.

122, 110501 (2019).

12-Qubit Linear Cluster state

8 CZ-gate layers to generate a 2D cluster state Always 3 layers

Strongly correlated quantum walks with a

12-qubit superconducting processor

1D chain quantum walk

One photon Two photons

Pulse sequence

One photon Two photons

1D chain quantum walk

One photon Two photonsZ. Yan et al., Science

10.1126/science.aaw1611 (2019).

10-Qubit Entanglement with a

Superconducting Circuit

10-Qubits processor with complete connection

Q1

Q2

Q3

Q4

Q5

Q6

Q7

Q8

Q9

Q10

CenterResonantor

GHZ state preparation

Full state tomography

10-bit GHZ state fidelity

is about 66%

PRL 119, 180511 (2017)SQ:arXiv:1905.00320, Ion trap:arXiv:1905.0572

2014

First transmon/Xmon

qubit T1~5μs,

T2*~2μs

Improve the coherence time

T1~15μs, T2*~ 10μs.

2015

4-Qubits processor

HHL algorithm demonstration

PRL 118, 210504 (2017)

2016 2018

2018

50-Qubits

PRL 119,180511(2017)

10-qubits entanglement

quantum Cloud

24-Qubits processor

12-engtanglement

PRL 122, 110501 (2019)

2020

Quantum

Supremacy

??

2015 2017

Summary

We designed and fabricated several versions of quantum

processor, on which integrated up to 24 quibts

The typical T1 and T2 time are both longer than 20 micro-

seconds

The single-bit gate fidelity is >99.9%, for the CZ gate it

reaches 99.5% in the best case, and for CCZ is ~93.3%

We generate a 10-qubit GHZ state with a fidelity of 0.668 ±0.025, further obtained a 12-qubit LC state with 0.707 ±0.008

We demonstrated Strongly correlated quantum walks with a

12-qubit superconducting processor

Experiments:Institute of Physics, Chinese Academy of Sciences, Beijing, China

Zhejiang University，Zhejiang,China

Micro-fabrication: The micro-fabrication lab on IOP-China, National Center for Nanoscience and Technology and USTC.

Theories:IOP-CAS, Beijing, China

Zhejiang University, Zhejiang, China

Nanjing University, Nanjing, China

Fuzhou University, Fuzhou, Fujian,China

Tsinghua University, Beijing, China

Beijing Computational Science Research Center

Hangzhou Normal University

University of Kansas, USA

Institute of Automation, Chinese Academy of Sciences

NTT Basic Research Laboratories, Atsugi, Japan

National Institute of Informatics,Tokyo, Japan

RIKEN, Japan

Acknowledgements

The project is supported by the

Chinese Academy of Science,

National Nature Science Foundation

of China, National Basic Research

Program, Alibaba Cloud, Science and

Technology Committee of Shanghai

Municipality, and Anhui Province.

Thank you for your attention!

4 bits HHL algorithm

4 qubits HHL algorithm

4 qubits HHL algorithm

4 qubits HHL algorithm

PRL 118.2105

04 (2017)

Quantum Switch by

Longitudinal Control Field

The principle of the switch

Qubit-Resonance

Qubit-Qubit

Avoid crossing and decoupling

Switching on/off the coherent oscillation

Switching on/off the coherent oscillation

“An efficient and compact quantum switch for quantum circuits”,

npj Quantum Information, 4:50, (2018).