量子雑音を抑えた高精度原子時計（MIT physicists improve atomic clocks’ precision）

2025-10-08 マサチューセッツ工科大学 (MIT)

MITの物理学者チームは、量子ノイズを抑制して光格子原子時計の精度を2倍に高める新手法「グローバル位相分光法（global phase spectroscopy）」を開発した。イッテルビウム原子の光学的振動にレーザー誘起の位相効果を利用し、量子増幅で安定化を実現。従来無視されていたレーザー–原子間相互作用を制御要素として活用した点が革新的である。この手法により、原子時計はより多くの「チック」を識別でき、可搬型高精度時計の実現が期待される。将来的にはダークマターや重力波、地震前兆の検出にも応用可能。成果は『Nature』誌に掲載。

The new method, which the researchers dub “global phase spectroscopy,” offers a way to keep an atomic clock’s laser highly stable.　Credit: Ryley McConkey

＜関連情報＞

光時計遷移における量子増幅グローバル位相分光法 Quantum-amplified global-phase spectroscopy on an optical clock transition

Leon Zaporski,Qi Liu,Gustavo Velez,Matthew Radzihovsky,Zeyang Li,Simone Colombo,Edwin Pedrozo-Peñafiel & Vladan Vuletić
Nature Published:08 October 2025
DOI:https://doi.org/10.1038/s41586-025-09578-8

Abstract

Optical lattice clocks are at the forefront of precision metrology^1,2,3,4,5,6, operating near a standard quantum limit set by quantum noise^4,7. Harnessing quantum entanglement offers a promising route to surpass this limit^{8,9,10,11,12,13,14,15}; however, there are practical difficulties in terms of scalability and measurement resolution requirements^16,17. Here we adapt the holonomic quantum gate concept¹⁸ to develop a new Rabi-type ‘global-phase spectroscopy’ that uses the detuning-sensitive global Aharonov–Anandan phase¹⁹. With this approach, we can demonstrate quantum-amplified time-reversal spectroscopy on an optical clock transition that achieves directly measured 2.4(7) dB metrological gain and 4.0(8) dB improvement in laser noise sensitivity beyond the standard quantum limit. To this end, we introduce rotary echo to protect the dynamics from inhomogeneities in light–atom coupling and implement a laser-noise-cancelling differential measurement through symmetric phase encoding in two nuclear spin states. Our technique is not limited by measurement resolution, scales easily because of the global nature of entangling interaction and exhibits high resilience to typical experimental imperfections. We expect it to be broadly applicable to next-generation atomic clocks and other quantum sensors approaching the fundamental quantum precision limits^20,21,22.

多体エンタングルメント状態を用いた時間反転に基づく量子計測 Time-reversal-based quantum metrology with many-body entangled states

Simone Colombo,Edwin Pedrozo-Peñafiel,Albert F. Adiyatullin,Zeyang Li,Enrique Mendez,Chi Shu & Vladan Vuletić
Nature Physics Published:14 July 2022
DOI:https://doi.org/10.1038/s41567-022-01653-5

Abstract

Linear quantum measurements with independent particles are bounded by the standard quantum limit, which limits the precision achievable in estimating unknown phase parameters. The standard quantum limit can be overcome by entangling the particles, but the sensitivity is often limited by the final state readout, especially for complex entangled many-body states with non-Gaussian probability distributions. Here, by implementing an effective time-reversal protocol in an optically engineered many-body spin Hamiltonian, we demonstrate a quantum measurement with non-Gaussian states with performance beyond the limit of the readout scheme. This signal amplification through a time-reversed interaction achieves the greatest phase sensitivity improvement beyond the standard quantum limit demonstrated to date in any full Ramsey interferometer. These results open the field of robust time-reversal-based measurement protocols offering precision not too far from the Heisenberg limit. Potential applications include quantum sensors that operate at finite bandwidth, and the principle we demonstrate may also advance areas such as quantum engineering, quantum measurements and the search for new physics using optical-transition atomic clocks.

光原子時計遷移におけるエンタングルメント Entanglement on an optical atomic-clock transition

Edwin Pedrozo-Peñafiel,Simone Colombo,Chi Shu,Albert F. Adiyatullin,Zeyang Li,Enrique Mendez,Boris Braverman,Akio Kawasaki,Daisuke Akamatsu,Yanhong Xiao & Vladan Vuletić
Nature Published:16 December 2020
DOI:https://doi.org/10.1038/s41586-020-3006-1

Abstract

State-of-the-art atomic clocks are based on the precise detection of the energy difference between two atomic levels, which is measured in terms of the quantum phase accumulated over a given time interval^1,2,3,4. The stability of optical-lattice clocks (OLCs) is limited both by the interrupted interrogation of the atomic system by the local-oscillator laser (Dick noise⁵) and by the standard quantum limit (SQL) that arises from the quantum noise associated with discrete measurement outcomes. Although schemes for removing the Dick noise have been recently proposed and implemented^4,6,7,8, performance beyond the SQL by engineering quantum correlations (entanglement) between atoms^{9,10,11,12,13,14,15,16,17,18,19,20} has been demonstrated only in proof-of-principle experiments with microwave clocks of limited stability. The generation of entanglement on an optical-clock transition and operation of an OLC beyond the SQL represent important goals in quantum metrology, but have not yet been demonstrated experimentally¹⁶. Here we report the creation of a many-atom entangled state on an OLC transition, and use it to demonstrate a Ramsey sequence with an Allan deviation below the SQL after subtraction of the local-oscillator noise. We achieve a metrological gain of 4.4^0.6_0.4 decibels over the SQL by using an ensemble consisting of a few hundred ytterbium-171 atoms, corresponding to a reduction of the averaging time by a factor of 2.8 ± 0.3. Our results are currently limited by the phase noise of the local oscillator and Dick noise, but demonstrate the possible performance improvement in state-of-the-art OLCs^1,2,3,4 through the use of entanglement. This will enable further advances in timekeeping precision and accuracy, with many scientific and technological applications, including precision tests of the fundamental laws of physics^21,22,23, geodesy^24,25,26 and gravitational-wave detection²⁷.