Andrew Ludlow, Time and Frequency Division, Nationwide Institute of Requirements and Know-how, Boulder, CO, USA
December 11, 2019• Physics 12, 141
An optical clock based mostly on an array of individually trapped atoms gives a brand new twist in atom-based timekeeping.
Determine 1: The brand new tweezer clock has the potential for low noise (excessive precision) as a result of the clock frequency from many atoms may be measured without delay. Additionally, since every atom is held in its personal tightly targeted laser beam (the tweezers), the atoms may be conveniently learn out with single-particle decision.The brand new tweezer clock has the potential for low noise (excessive precision) as a result of the clock frequency from many atoms may be measured without delay. Additionally, since every atom is held in its personal tightly targeted laser beam (the tweezers), the atoms may be convenien… Present extra
Determine 1: The brand new tweezer clock has the potential for low noise (excessive precision) as a result of the clock frequency from many atoms may be measured without delay. Additionally, since every atom is held in its personal tightly targeted laser beam (the tweezers), the atoms may be conveniently learn out with single-particle decision.×
Higher clocks are at all times in demand. That’s as a result of precision timekeeping may be leveraged for thus many purposes, starting from navigation and communication networks to radio astronomy and searches for beyond-standard-model physics. At this time’s most exact clocks are optical clocks with trapped atoms, which use the optical frequency of an electron transitioning between two atomic states because the timebase. Every cycle of this frequency gives a really exact “tick” of the clock. Amongst superior optical atomic clocks, researchers have largely targeted on two varieties: people who probe an electron of only a single trapped atom (particularly, an ion) and people who probe the electrons of many atoms trapped in interfering laser beams (an optical lattice.) Now, two teams have launched a 3rd sort of trapped-atom optical clock into the timekeeping panorama [1, 2]. The brand new “tweezer clock” includes many separate optical traps, often called optical tweezers, however every entice incorporates just one atom. This new structure captures a number of the greatest options of the single-atom and optical lattice approaches.
The first benefits of basing a clock on a single ion are that the particle may be exactly manipulated and remoted from the skin world, which collectively restrict results that distort the electron’s ticking fee (and thus the clock’s accuracy). Nonetheless, the precision of such clocks is basically restricted by the quantum uncertainty of the atom’s state . With optical lattice clocks, this so-called quantum projection noise may be averaged away by probing the frequency of hundreds (or extra) atoms without delay. In comparison with the single-atom case, the noise drops by the sq. root of the variety of atoms, resulting in higher precision inside a given measurement time. The draw back of the lattice method is that the atoms within the lattice can doubtlessly work together with one another, perturbing the electron ticking fee. Usually, one additionally loses the flexibility to manage or learn out the states of particular person atoms  (see 5 March 2018 Viewpoint). These options would in any other case be helpful for enhancing clock operation and efficiency.
The optical tweezer clock provides an intriguing compromise between the single-ion and lattice approaches. An optical tweezer is a tightly targeted laser beam that may pull atoms (or different small objects) to its narrowest level. Manuel Endres on the California Institute of Know-how, Pasadena, and colleagues developed an experimental clock that makes use of a 1D array of 81 such tweezers, with about half of those containing a single atom. This variety of atoms is excessive sufficient to scale back quantum noise by a few issue of 6 in contrast with the single-atom case. The atoms are additionally nicely spaced (by a number of micrometers), suppressing disruptive atomic interactions. What’s extra, the clock provides single-particle learn out for every tweezer.
Establishing the brand new clock entails just a few steps. The researchers start by laser cooling a fuel of strontium, an atomic species whose digital construction is nicely suited to an optical clock. They then load the chilly atoms into the array of practically an identical optical tweezers, that are shaped by passing a laser by way of an acousto-optic deflector and an goal lens (Fig. 1). The loading course of doesn’t, nonetheless, assure one atom per tweezer—some have zero, whereas others have a number of atoms. The researchers due to this fact use an extra laser to kick out atoms the place there’s an extra, leaving empty tweezers unfilled. Lastly, the group “interrogates” every tweezer’s atom. This course of entails tuning a laser frequency till the atom is worked up and its fluorescence may be detected (learn out) with a digicam.
Following a recipe reported beforehand , Endres’ group employs a nondestructive read-out scheme that permits them to interrogate and skim out the atoms a number of occasions earlier than loss mechanisms require reloading a brand new group of atoms into the tweezers. Due to the single-particle read-out functionality of their setup, they can measure small shifts within the clock transition that come up from the tweezer’s optical discipline  and to find out how these shifts range from tweezer to tweezer. Related measurements may very well be used to detect electromagnetic discipline gradients or different inhomogeneities that perturb the clock. The group can be capable of characterize the clock’s stability. Though they discover a worth that’s greater than an order of magnitude worse than for one of the best atom clocks, enhancements might be potential with a much less noisy clock laser. Additional progress will doubtless come from utilizing bigger arrays and making quantum enhancements.
In a separate paper reported in October, Adam Kaufman and collaborators at JILA and the College of Colorado Boulder, additionally demonstrated a tweezer clock utilizing strontium . Most of the important particulars of their clock have been related. However they targeted on a smaller array (roughly 5 atoms). Additionally they employed a complicated cavity-stabilized clock laser, enabling coherence-preserving atomic interrogations of as much as 4 seconds—a powerful quantity not just for a tweezer clock however for any optical clock. Underneath these situations, the group achieved higher frequency stability than the Endres group, and the steadiness was restricted fully by projection noise.
A aim for the long run is to mix single-particle learn out with single-particle interrogation and management. Such management might make the optical tweezer clock a handy platform for multi-ensemble protocols that will provide massive boosts in clock efficiency, together with prolonged interrogation schemes  and zero-dead-time configurations . Optical tweezer arrays present an rising platform for exploring quantum computation and simulation in addition to quantum-enhanced measurements. Advances in any certainly one of these areas will undoubtedly feed into the others. For instance, entanglement-enhanced measurements could translate properly to an optical tweezer clock, providing advances in clock precision.
Scaling the tweezer clock as much as bigger atom numbers is a crucial subsequent step with a purpose to attain the decrease quantum-noise ranges accessible with lattice clocks. At this time’s lattice clocks usually make use of hundreds of atoms or extra and reaching this quantity with tweezer clocks might be a problem, partly due to technical limitations on the laser energy required to kind the tweezers. However the 1D tweezer clock now demonstrated may be naturally scaled to a 2D array, whereas nonetheless preserving the advantages of single-particle learn out. Given all the probabilities for future enhancements to the tweezer clock, it’s clear that this new method to timekeeping and quantum management has an intriguing future.
This analysis is printed in Bodily Evaluation X and Science.
I. S. Madjarov, A. Cooper, A. L. Shaw, J. P. Covey, V. Schkolnik, T. H. Yoon, J. R. Williams, and M. Endres, “An atomic-array optical clock with single-atom readout,” Phys. Rev. X 9, 041052 (2019).M. A. Norcia, A. W. Younger, W. J. Eckner, E. Oelker, J. Ye, and A. M. Kaufman, “Seconds-scale coherence on an optical clock transition in a tweezer array,” Science 366, 93 (2019).W. M. Itano, J. C. Bergquist, J. J. Bollinger, J. M. Gilligan, D. J. Heinzen, F. L. Moore, M. G. Raizen, and D. J. Wineland, “Quantum projection noise: Inhabitants fluctuations in two-level programs,” Phys. Rev. A 47, 3554 (1993).G. E. Marti, R. B. Hutson, A. Goban, S. L. Campbell, N. Poli, and J. Ye, “Imaging optical frequencies with 100 𝜇Hz precision and 1.1 𝜇m decision,” Phys. Rev. Lett. 120, 103201 (2018).J. P. Covey, I. S. Madjarov, A. Cooper, and M. Endres, “2000-times repeated imaging of strontium atoms in clock-magic tweezer arrays,” Phys. Rev. Lett. 122, 173201 (2019).H. Katori, M. Takamoto, V. G. Pal’chikov, and V. D. Ovsiannikov, “Ultrastable optical clock with impartial atoms in an engineered gentle shift entice,” Phys. Rev. Lett. 91, 173005 (2003).D. B. Hume and D. R. Leibrandt, “Probing past the laser coherence time in optical clock comparisons,” Phys. Rev. A 93, 032138 (2016).M. Schioppo et al., “Ultrastable optical clock with two cold-atom ensembles,” Nat. Photon. 11, 48 (2016).
Concerning the Writer
Andrew Ludlow is a analysis physicist within the Time and Frequency Division on the Nationwide Institute of Requirements and Know-how (NIST) and a lecturer within the Physics Division on the College of Colorado Boulder. His principal analysis pursuits embody the event of optical atomic clocks, chilly atom programs for quantum metrology, and ultrastable optical sources and laser interferometry. He joined NIST in 2008 after receiving a Ph.D. in physics from the College of Colorado, and he at the moment leads the event of the ytterbium optical lattice clock there.
Atomic and Molecular Physics