22–26 Nov 2021
AlbaNova Main Building
Europe/Stockholm timezone
Please note: ECTI 2021 will be held as a hybrid event.

A low-noise, ultrastable 674 nm laser for quantum metrology with entangled 88Sr+ ions

22 Nov 2021, 13:10
20m
Tsuzuki Lecture Theatre, St. Anne's college (Oxford + Zoom)

Tsuzuki Lecture Theatre, St. Anne's college

Oxford + Zoom

Speaker

Guido Wilpers (National Physical Laboratory)

Description

Optical qubit transitions in laser-cooled, trapped ions are used in precision quantum metrology [1] and in quantum information processing [2,3]. In linear ion strings, each qubit and the quantised collective motion are controlled coherently via the ion-laser laser interaction to create scalable entanglement. Such systems could realise a gain in precision and overcome the quantum projection noise limitation in single ion clocks [1] to reach their systematic uncertainty level at 10-18 with short averaging timescales.
For precision spectroscopy utilising scalable entanglement of trapped-ion optical qubits, the ultrastable frequency typical of optical clock lasers is necessary, but on its own is insufficient. Two further challenges need to be addressed.
Firstly, minimal noise at high Fourier frequencies is essential, as noise at frequencies in the MHz range causes off-resonant ion-laser interactions, which degrade the fidelity of entanglement operations utilising motional sidebands of the ion crystal. Such noise is typically present in semiconductor laser systems [3]. Secondly, a high-power source is required to generate laser pulses that are agile in amplitude, phase and frequency, and which illuminate an ion string evenly with the requisite Rabi frequency.
We report on the realisation of an ultrastable 674 nm laser suited for the optical qubit transition in 88Sr+. We use a commercial Ti:sapphire laser source optimised for the low wavelength end of its gain range. Stabilisation to a high-finesse, low-drift cavity, including fast feedback to an external AOM, results in a 1 Hz fluctuation of the optical frequency measured from 1 s to beyond 100 s averaging times. We evaluated the noise at Fourier frequencies out to 10 MHz and find it to be mostly below a white frequency noise level of a few HzHz-1/2. With 1 W of spectrally pure cw laser light at the 1 Hz level at our disposal we could supply up to four independent systems, each delivering tens of milliwatts of stable and fully agile light to trapped ions.
Our measurements show the characteristically rapid decrease of intrinsic noise towards high Fourier frequencies for this type of laser. Following the argument in [4] they would indicate that a infidelity contribution of ≤ $2\dot10^{-4}$ from off-resonant excitation at 1 MHz can be achieved without the need for further spectral filtering [3].
References [1] S. M. Brewer, et al. Phys. Rev. Lett. 123 033201 (2019). [2] Th. Monz, et al. Science 351 1068 (2016). [3] N. Akerman, et al. New J. Phys. 17 113060 (2015). [4] J. Benhelm, et al. Nat. Phys. 4 463 (2008).

Primary author

Guido Wilpers (National Physical Laboratory)

Co-authors

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