ITU Workshop on Quantum Information Technology (QIT) for Networks Shanghai, China, 5th June 2019

Superconducting Quantum Computing Xiaobo Zhu CAS Center for Excellence in Quantum Information and Quantum Physics University of Science and Technology of China

Email: [email protected] How to scale up?

Ultra-high precision More qubits and longer depth analog circuit • Better pulse calibration • Less crosstalk • Less state leakage • Higher readout efficiency • Less TLS • Deeper connectivity …… Sample Fabrication

To stabilize the sample parameters To speed up the development of new samples Qubit Samples

Longer T1: ~5us T1: ~15us T1: ~40us Coherent time

More 3 Bits 5 Bits 6 Bits 9 Bits 10 Bits 12 Bits 24 Bits 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 4.978 4.183 5.192 4.352 5.11 4.226 5.03 4.3 5.142 4.14 4.996 4.26 (GHz) f_ah -247.7 -203.5 -245.7 -202.7 -246.9 -201.5 -245.8 -203 -243.5 -203.4 -246.4 -201.4 (MHz)

T1 ~ 30us-50us * T2 > 20us at optimal point The fidelity of single-qubit gates operation

Q7 at optimal point Q7 at optimal point Q7 at optimal point

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

Q7 at optimal point 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

~32ns Ts =1/(2g11,20)~32ns g11,20=15.6MHz

Tgate=40ns~1.25Ts CCZ gate CCZ gate fidelity

F=93.3%(experiment),78.5ns and F=99.3%(numeric) Conclusion of nonadiabatic way

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

“Realization of high-fidelity nonadiabatic CZ gates with superconducting qubits”, submitted 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 ⊗푁 ⊗푁 • Greenberger-Horne-Zeilinger (GHZ) state: 퐺퐻푍N = ( 0 + 1 )/ 2 10-qubit GHZ in superconducting

14-qubit GHZ in ion trap 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

State preparation error

Readout error

Triple the length, more ZZ coupling

Gate fidelity 12-Qubit Linear Cluster state

Only two local measurement settings*

*Phys. Rev. Lett. 94, 060501 (2005) Phys. Rep. 474, 1 (2009) 12-Qubit Linear Cluster state

LC state fidelity

Over 55% for 12-qubit LC state, 250,000 projective measurements 21 statistical standard deviations above 50% 12-Qubit Linear Cluster state 12-Qubit Linear Cluster state

0.707(8)

Phys. Rev. Lett. 122, 110501 (2019).

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

Two photons One photon Z. Yan et al., Science 10.1126/science.aaw1611 (2019). 10-Qubit Entanglement with a Superconducting Circuit 10-Qubits processor with complete connection

Q3

Q2 Q4

Q1 Q5 Center Resonantor Q10 Q6

Q9 Q7

Q8 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 2015 2016 2018 2020 ?? Improve the coherence time HHL algorithm demonstration quantum Cloud T1~15μs, T2*~ 10μs. PRL 118, 210504 (2017) Quantum 50-Qubits Supremacy

First transmon/Xmon 4-Qubits processor qubit T1~5μs, 10-qubits entanglement 24-Qubits processor T2*~2 s 12-engtanglement μ PRL 119,180511(2017) PRL 122, 110501 (2019) 2014 2015 2017 2018 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 Acknowledgements

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 The project is supported by the Fuzhou University, Fuzhou, Fujian,China Chinese Academy of Science, Tsinghua University, Beijing, China National Nature Science Foundation Beijing Computational Science Research Center Hangzhou Normal University of China, National Basic Research University of Kansas, USA Program, Alibaba Cloud, Science and Institute of Automation, Chinese Academy of Sciences Technology Committee of Shanghai NTT Basic Research Laboratories, Atsugi, Japan Municipality, and Anhui Province. National Institute of Informatics,Tokyo, Japan RIKEN, Japan 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).