September 28, 2022

Quantum Algorithms Bring Ions to a Standstill – Towards Even More Accurate Optical Atomic Clocks

They can also assist to draw out kinetic energy from the mismatched ion pair. Throughout the procedure of so-called algorithmic cooling, quantum operations are utilized to do simply that: to move the energy from the hardly coolable motion of the spectroscopy ion to the quickly coolable movement of the logic ion.
And they managed to do this exceptionally well: “We were able to draw out so much energy from the pair of ions– including a singly charged beryllium ion and an extremely charged argon ion– that their temperature level lastly dropped to only 200 µK,” said one of QUESTs PhD students Lukas Spieß. Such an ensemble has never ever been so near outright zero (as in: so motionless). “What is more, we also observed an unprecedentedly low level of electric-field noise,” he broadened. This sound generally results in the ions being heated when the cooling stops, however this turns out to be particularly low in their apparatus. Integrating these two things suggests that the last significant difficulty in their way has now been gotten rid of, and an optical atomic clock that is based upon extremely charged ions can be built. This atomic clock might reach an unpredictability of less than 10– 18. Only the finest optical atomic clocks in the world are presently able to reach this kind of performance. These findings are likewise of excellent significance for the advancement of quantum computers and for precision spectroscopy.
Reference: “Algorithmic Ground-state Cooling of Weakly-Coupled Oscillators using Quantum Logic” by Steven A. King, Lukas J. Spieß, Peter Micke, Alexander Wilzewski, Tobias Leopold, José R. Crespo López-Urrutia and Piet O. Schmidt, 10 December 2021, Physical Review X.DOI: 10.1103/ PhysRevX.11.041049.

Mismatched partners are being cooled: A single beryllium ion (red, left) and a single highly charged argon ion (purple, ideal) are bombarded by lasers from numerous sides and are practically brought to a total dead stop. Credit: PTB
QUEST scientists conquer a major hurdle on the journey towards much more accurate optical atomic clocks.
Laser beams can do more than just heat things up; they can cool them down too. That is absolutely nothing brand-new for physicists who have actually committed themselves to precision spectroscopy and the development of optical atomic clocks. However what is brand-new is the very low temperature level that researchers at the QUEST Institute at the Physikalisch-Technische Bundesanstalt (PTB) have been able to reach with their extremely charged ions– this type of ion has never been cooled off as far as 200 µK before. The team dealing with this prospered by integrating their developed techniques that include the laser cooling of coupled ions and approaches from the field of quantum computing. The application of quantum algorithms made sure that ions that are too dissimilar for conventional laser cooling to work successfully could be cooled down together after all. This suggests that we are getting closer to an optical atomic clock with highly charged ions, and this clock may have the potential to be much more precise than existing optical atomic clocks. The results have actually been released in the current issue of Physical Review X.
If you want to investigate particles– such as ions– very accurately (state, using accuracy spectroscopy or for measuring their frequency in an atomic clock), then you have to bring them as close as you can to a dead stop. That is why pairs of paired ions have been utilized at the QUEST Institute for a long time in order to conquer this: One ion (called the “cooling ion” or the “reasoning ion”) is cooled by lasers; simultaneously, its combined partner ion is likewise cooled and can then be investigated spectroscopically (thus, it is called the “spectroscopy ion”). “But it is now these very ions that are particularly interesting for our research, for circumstances, for developing novel optical clocks,” describes QUEST physicist Steven King.

What is brand-new is the very low temperature that scientists at the QUEST Institute at the Physikalisch-Technische Bundesanstalt (PTB) have actually been able to reach with their highly charged ions– this type of ion has never ever been cooled down as far as 200 µK prior to. The application of quantum algorithms ensured that ions that are too different for traditional laser cooling to work efficiently might be cooled down together. That is why sets of paired ions have been utilized at the QUEST Institute for a long time in order to overcome this: One ion (called the “cooling ion” or the “logic ion”) is cooled by lasers; simultaneously, its combined partner ion is likewise cooled and can then be examined spectroscopically (for this reason, it is called the “spectroscopy ion”). During the process of so-called algorithmic cooling, quantum operations are utilized to do simply that: to move the energy from the hardly coolable motion of the spectroscopy ion to the quickly coolable motion of the logic ion.
And they managed to do this incredibly well: “We were able to extract so much energy from the pair of ions– consisting of a singly charged beryllium ion and a highly charged argon ion– that their temperature level finally dropped to only 200 µK,” stated one of QUESTs PhD trainees Lukas Spieß.

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