Synopsis: Simple Molecules for Accurate Clocks

Researchers propose using one-electron molecules for a new class of ultrahigh-precision clocks.
Synopsis figure
S. Schiller et al., Phys. Rev. Lett (2014)

Are fundamental constants really constant in time and space? Answering this question requires measurements of quantities such as the electron-proton mass ratio with extraordinary accuracy. One method is to look for small changes in molecular vibrational frequencies, but improved measurements will require a new generation of clocks. The cesium clock, with an uncertainty of few parts in 1016, is the best atomic clock suitable for such tests. Writing in Physical Review Letters, Stephan Schiller of the Heinrich Heine University Düsseldorf, Germany, and colleagues propose that clocks based on some of the simplest molecules [molecular hydrogen (H2+) and hydrogen-deuterium (HD+)] may allow researchers to eventually achieve uncertainties at the 1×10-17 level, outperforming existing schemes based on atomic transitions.

One-electron hydrogenlike molecules have a key advantage: their properties can be calculated with high accuracy, allowing an optimal selection of molecular transition frequencies. And what may seem like a disadvantage—the complexity of a molecule versus an atom—can actually improve accuracy: a subset of the many molecular transition lines can exhibit very low sensitivity to external electric and magnetic fields. The researchers propose an additional trick: a “composite frequency” method in which a clock’s frequency results from the weighted sum of multiples of these “robust” frequencies. Since the shifts of these transitions due to perturbations have different values, they can cancel out to yield a composite frequency with much-improved accuracy.

The authors calculated that a multiple-transition clock based on HD+ and H2+ would feature a 60-fold and 3-fold accuracy improvement compared to a single-transition clock, leading to an uncertainty of 5×10-18 and less than 2×10-17, respectively. The gain comes at the cost of additional complexity due to the multiple spectroscopic sources needed for the clock’s functioning, but preliminary experiments in the authors’ labs show show setting up such schemes is technologically feasible. – David Voss


Announcements

More Announcements »

Subject Areas

Atomic and Molecular Physics

Previous Synopsis

Metamaterials

Sound Switch

Read More »

Next Synopsis

Related Articles

Viewpoint: Superfluids Hit the Street
Atomic and Molecular Physics

Viewpoint: Superfluids Hit the Street

A flow pattern dubbed the von Kármán vortex street, which is renowned for its aesthetic beauty and extreme power, has been created in a superfluid. Read More »

Viewpoint: Lamb Shift Spotted in Cold Gases
Atomic and Molecular Physics

Viewpoint: Lamb Shift Spotted in Cold Gases

Cold atomic gases exhibit a phononic analog of the Lamb shift, in which energy levels shift in the presence of the quantum vacuum. Read More »

Synopsis: Quantum Droplets Swell to a Macrodrop
Atomic and Molecular Physics

Synopsis: Quantum Droplets Swell to a Macrodrop

Experiments with ultracold magnetic atoms reveal liquid-like quantum droplets that are 20 times larger than previously observed droplets.    Read More »

More Articles