Listening to an atom

I invite the reader to appreciate that there is an intricate clockwork ticking within each atom or molecule. This clockwork is affected by interactions of all atomic and subatomic particles that make up the atom. This clockwork is also minutely affected by the properties of the physical vacuum that spawns both familiar and yet undiscovered particles. By carefully listening to the atom, we may discover new physics. Such an approach naturally complements that of particle colliders that smash particles together. Atomic physics approach is subtler. We might not directly see the Higgs boson or some new particle, but we may "hear" it.

We carry out comprehensive theoretical studies aimed at both improving our “listening to the atom” tools and also at the interpretation of precision atomic experiments searching for new physics. These topics naturally fit into the broad context of precision measurements, a longtime and exceptionally fruitful atomic physics tradition. They also overlap with topics in quantum information processing and atomic timekeeping.

Atomic clocks

Atomic clocks are arguably the most precise scientific instruments ever built. Their exquisite  precision  has enabled both foundational tests  of modern physics, e.g., probing hypothetical drift of fundamental constants and practical applications, such as the global positioning system.  As the progress in timekeeping intimately relies on understanding  basic physics and ultimate perfection of experimental tools based on such an understanding,  the development of atomic clocks has been celebrated by several Nobel prizes, including this year's prize.

Over the past decade our  theory group  contributed to development of several clocks such as the microwave Cs standard and optical lattice clocks (in particular we proposed the  Yb and Hg lattice clocks, which are "ticking away" in  several labs around the world). We also invented micro-magic clocks and clocks with highly-charged ions.  Our proposed nuclear and highly-charged-ion clocks hold an intriguing promise of extending the accuracy frontier in  timekeeping.

Tests of fundamental symmetries with atoms and molecules

Atomic physics places powerful constraints on “new physics” beyond the standard model of elementary particles. There are a number of atomic physics experiments (including on-going experiments at Princeton, Yale, Harvard, Penn State, UT-Austin, Bolder and elsewhere) probing violations of fundamental symmetries (parity- and time-reversal). While the atomic energies are of an eV scale, the modern precision results constrain new physics at a TeV mass scale.  For example, in our refined analysis of C. Wieman experiment on atomic parity violation, we constrained the mass of the so-far elusive particle - the extra Z boson (Z'). Z' are hypothesized to be carriers of the “fifth force” of Nature, and they are abundant in models of grand unification and string theories. In particular, we raised the lower mass limit previously coming from the direct search at the Tevatron collider. Our raised bound on the Z' mass carves out a lower-energy part of the discovery reach of the Large Hadron Collider.

Ultralight dark matter searches with precision measurements

Multiple observations indicate that dark matter (DM) constitutes the dominant fraction (85%) of all matter in the Universe.  All the current evidence for DM comes from galactic or larger scale observations, leaving the microscopic nature of DM a mystery. Conclusive evidence for DM in terrestrial experiments remains elusive.  Theoretically, there is a truly large variety of DM candidates, ranging from elementary particles to black holes. Even if DM is composed of particles, the plausible masses of candidates span sixty(!) orders of magnitudes. Considering this variety of models and the associated large range of non-gravitational interactions of DM with ordinary matter, it is important to constrain DM models by creatively reanalyzing existing data. Compared to investments into dedicated experiments, this is a relatively low-cost strategy with tantalizing potential for discovery.

Our GPS.DM collaboration pursues a strategy of confronting predictions of certain DM models with the analysis of existing data. The strategy relies on searching for expected space-time signatures of DM interacting with precision measurement devices, such as atomic clocks. The data sets could have been recorded for other purposes, e.g., time-keeping. Typically, an unsuspecting experimentalist would characterize small unexplained perturbations in their experimental data as noise. We correlate "noise'" to determine if the correlations exhibit patterns characteristic of DM. If the sought DM signature is found, this would constitute a far-reaching discovery. If not, we constrain strengths of specific non-gravitational DM-ordinary matter interactions.

Quantum information processing

One of the important directions in modern atomic physics is quantum information processing (QIP). Internal atomic and molecular levels naturally serve as qubits with long coherence times. QIP with neutral atoms has a number of appealing advantages: scalability, massive parallelism, long coherence times and reliance on well-established experimental techniques. Historically most of QIPschemes with neutral atoms have focused on alkali-metal atoms (atoms with a single valence electron outside a tightly-bound atomic core). Yet over the past several years there were new powerful developments with cooling and trapping divalent atoms ( alkaline-earth and similar atoms), including attainment of degenerate quantum gasses and a rapid development of a novel ultrastable class of atomic clocks: optical lattice clocks.

While with the alkali-metal atoms there were numerous theoretical proposals for two-qubit gate operation, the most successful experimental demonstration of quantum two-qubit logic gate with neutral atoms has been carried out using a specific technique: Rydberg blockade. It is natural to wonder if the distinct properties of divalent atoms could dramatically improve the experimental feasibility.

We employ tools of modern atomic  physics to develop new approaches to quantum information processing with neutral atoms. We will study the feasibility of realizing multi-qubit gates using Rydberg states of divalent atoms, i.e., we will be building upon the only experimentally-demonstrated gate in alkalis and exploring various ways of how the feasibility can be improved by moving to divalent atoms.

We also expand on our earlier work on decoherence-free "magic" trapping of atoms in optical traps and develop a decoherence-free Rydberg logic and quantum memory insensitive to otherwise detrimental trapping fields.