原子時計と量子コンピューターの融合(Merging Atomic Clocks with Quantum Computers)

2024-10-09 カリフォルニア工科大学(Caltech)

＜関連情報＞

• https://www.caltech.edu/about/news/merging-atomic-clocks-with-quantum-computers
• https://www.nature.com/articles/s41586-024-08005-8
• https://www.nature.com/articles/s41586-024-07913-z

ピンセットクロックのための普遍的量子演算とアンシラベースの読み出し Universal quantum operations and ancilla-based read-out for tweezer clocks

Ran Finkelstein,Richard Bing-Shiun Tsai,Xiangkai Sun,Pascal Scholl,Su Direkci,Tuvia Gefen,Joonhee Choi,Adam L. Shaw & Manuel Endres
Nature  Published:09 October 2024
DOI:https://doi.org/10.1038/s41586-024-08005-8

Abstract

Enhancing the precision of measurements by harnessing entanglement is a long-sought goal in quantum metrology^1,2. Yet attaining the best sensitivity allowed by quantum theory in the presence of noise is an outstanding challenge, requiring optimal probe-state generation and read-out strategies^3,4,5,6,7. Neutral-atom optical clocks⁸, which are the leading systems for measuring time, have shown recent progress in terms of entanglement generation^9,10,11 but at present lack the control capabilities for realizing such schemes. Here we show universal quantum operations and ancilla-based read-out for ultranarrow optical transitions of neutral atoms. Our demonstration in a tweezer clock platform^{9,12,13,14,15,16} enables a circuit-based approach to quantum metrology with neutral-atom optical clocks. To this end, we demonstrate two-qubit entangling gates with 99.62(3)% fidelity—averaged over symmetric input states—through Rydberg interactions^15,17,18 and dynamical connectivity¹⁹ for optical clock qubits, which we combine with local addressing¹⁶ to implement universally programmable quantum circuits. Using this approach, we generate a near-optimal entangled probe state^1,4, a cascade of Greenberger–Horne–Zeilinger states of different sizes, and perform a dual-quadrature⁵ Greenberger–Horne–Zeilinger read-out. We also show repeated fast phase detection with non-destructive conditional reset of clock qubits and minimal dead time between repetitions by implementing ancilla-based quantum logic spectroscopy²⁰ for neutral atoms. Finally, we extend this to multi-qubit parity checks and measurement-based, heralded, Bell-state preparation^21,22,23,24. Our work lays the foundation for hybrid processor–clock devices with neutral atoms and more generally points to a future of practical applications for quantum processors linked with quantum sensors²⁵.

光クロックにおけるマルチ量子ゲートとシュレーディンガー猫の状態 Multi-qubit gates and Schrödinger cat states in an optical clock

Alec Cao,William J. Eckner,Theodor Lukin Yelin,Aaron W. Young,Sven Jandura,Lingfeng Yan,Kyungtae Kim,Guido Pupillo,Jun Ye,Nelson Darkwah Oppong & Adam M. Kaufman
Nature  Published:09 October 2024
DOI:https://doi.org/10.1038/s41586-024-07913-z

Abstract

Many-particle entanglement is a key resource for achieving the fundamental precision limits of a quantum sensor¹. Optical atomic clocks², the current state of the art in frequency precision, are a rapidly emerging area of focus for entanglement-enhanced metrology^3,4,5,6. Augmenting tweezer-based clocks featuring microscopic control and detection^7,8,9,10 with the high-fidelity entangling gates developed for atom-array information processing^11,12 offers a promising route towards making use of highly entangled quantum states for improved optical clocks. Here we develop and use a family of multi-qubit Rydberg gates to generate Schrödinger cat states of the Greenberger–Horne–Zeilinger (GHZ) type with up to nine optical clock qubits in a programmable atom array. In an atom-laser comparison at sufficiently short dark times, we demonstrate a fractional frequency instability below the standard quantum limit (SQL) using GHZ states of up to four qubits. However, because of their reduced dynamic range, GHZ states of a single size fail to improve the achievable clock precision at the optimal dark time compared with unentangled atoms¹³. Towards overcoming this hurdle, we simultaneously prepare a cascade of varying-size GHZ states to perform unambiguous phase estimation over an extended interval^14,15,16,17. These results demonstrate key building blocks for approaching Heisenberg-limited scaling of optical atomic clock precision.