Yuwei Ma

In the relentless pursuit of quantum computational advantage, we present a significant advancement with the development of Zuchongzhi 3.0. This superconducting quantum computer prototype, comprising 105 qubits, achieves high operational fidelities, with single-qubit gates, two-qubit gates, and readout fidelity at 99.90%, 99.62%, and 99.13%, respectively. Our experiments with an 83-qubit, 32-cycle random circuit sampling on the Zuchongzhi 3.0 highlight its superior performance, achieving 1×10^{6} samples in just a few hundred seconds. This task is estimated to be infeasible on the most powerful classical supercomputers, Frontier, which would require approximately 5.9×10^{9} yr to replicate the task. This leap in processing power places the classical simulation cost 6 orders of magnitude beyond Google's SYC-67 and SYC-70 experiments [Morvan et al., Nature 634, 328 (2024)10.1038/s41586-024-07998-6], firmly establishing a new benchmark in quantum computational advantage. Our work not only advances the frontiers of quantum computing but also lays the groundwork for a new era where quantum processors play an essential role in tackling sophisticated real-world challenges.

A quantum version of generative adversarial learning is experimentally demonstrated with a superconducting circuit.

Schrödinger's cat originates from the famous thought experiment querying the counterintuitive quantum superposition of macroscopic objects. As a natural extension, several "cats" (quasi-classical objects) can be prepared into coherent quantum superposition states, which is known as multipartite cat states demonstrating quantum entanglement among macroscopically distinct objects. Here, we present a highly scalable approach to deterministically create flying multipartite Schrödinger's cat states by reflecting coherent-state photons from a microwave cavity containing a superconducting qubit. We perform full quantum state tomography on the cat states with up to four photonic modes and confirm the existence of quantum entanglement among them. We also witness the hybrid entanglement between discrete-variable states (the qubit) and continuous-variable states (the flying multipartite cat) through a joint quantum state tomography. Our work provides an enabling step for implementing a series of quantum metrology and quantum information processing protocols based on cat states.

The fluxonium qubit is a promising candidate for quantum computation due to its long coherence times and large anharmonicity. We present a tunable coupler that realizes strong inductive coupling between two heavy-fluxonium qubits, each with approximately <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><a:mn>50</a:mn></a:math>-MHz frequencies and approximately <d:math xmlns:d="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><d:mn>5</d:mn></d:math>-GHz anharmonicities. The coupler enables the qubits to have a large tuning range of <g:math xmlns:g="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><g:mi>X</g:mi><g:mi>X</g:mi></g:math> coupling strengths (<j:math xmlns:j="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><j:mo>−</j:mo><j:mn>35</j:mn></j:math> to 75 MHz). The <m:math xmlns:m="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><m:mi>Z</m:mi><m:mi>Z</m:mi></m:math> coupling strength is <p:math xmlns:p="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><p:mo>&lt;</p:mo><p:mn>3</p:mn></p:math> kHz across the entire coupler bias range and <s:math xmlns:s="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><s:mo>&lt;</s:mo><s:mn>100</s:mn></s:math> Hz at the coupler off position. These qualities lead to fast high-fidelity single- and two-qubit gates. By driving at the difference frequency of the two qubits, we realize a <v:math xmlns:v="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><v:msqrt><v:mi>i</v:mi><v:mrow><v:mstyle mathsize="0.85em"><v:mi>SWAP</v:mi></v:mstyle></v:mrow></v:msqrt></v:math> gate in 258 ns with fidelity 99.72%, and by driving at the sum frequency of the two qubits, we achieve a <z:math xmlns:z="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><z:msqrt><z:mi>b</z:mi><z:mrow><z:mstyle mathsize="0.85em"><z:mi>SWAP</z:mi></z:mstyle></z:mrow></z:msqrt></z:math> gate in 102 ns with fidelity 99.91%. This latter gate is only five qubit Larmor periods in length. We run cross-entropy benchmarking for over 20 consecutive hours and measure stable gate fidelities, with <db:math xmlns:db="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><db:msqrt><db:mi>b</db:mi><db:mrow><db:mstyle mathsize="0.85em"><db:mi>SWAP</db:mi></db:mstyle></db:mrow></db:msqrt></db:math> drift (<hb:math xmlns:hb="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><hb:mn>2</hb:mn><hb:mi>σ</hb:mi></hb:math>) <kb:math xmlns:kb="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><kb:mo>&lt;</kb:mo><kb:mn>0.02</kb:mn><kb:mi mathvariant="normal">%</kb:mi></kb:math> and <ob:math xmlns:ob="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><ob:msqrt><ob:mi>i</ob:mi><ob:mrow><ob:mstyle mathsize="0.85em"><ob:mi>SWAP</ob:mi></ob:mstyle></ob:mrow></ob:msqrt></ob:math> drift <sb:math xmlns:sb="http://www.w3.org/1998/Math/MathML" display="inline" overflow="scroll"><sb:mo>&lt;</sb:mo><sb:mn>0.08</sb:mn><sb:mi mathvariant="normal">%</sb:mi></sb:math>. Published by the American Physical Society 2024