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Hyperfine-induced electric dipole contributions may significantly increase probabilities of otherwise very weak electric octupole and magnetic quadrupole atomic clock transitions (e.g. transitions between $s$ and $f$ electron orbitals).…

Following a suggestion of Kostelecky et al. we have evaluated a test of CPT and Lorentz invariance from the microwave spectroscopy of muonium. Hamiltonian terms beyond the standard model violating CPT and Lorentz invariance would contribute…

Theories unifying gravity with other interactions suggest spatial and temporal variation of fundamental "constants" in the Universe. A change in the fine structure constant, alpha, could be detected via shifts in the frequencies of atomic…

Atomic clocks use atomic transitions as frequency references. The susceptibility of the atomic transition to external fields limits clock stability and introduces systematic frequency shifts. Here, we propose to realize an atomic clock that…

Optical clocks have achieved remarkable estimated fractional frequency uncertainties reaching the $10^{-18}$ level and below, enabling applications in fundamental physics, general relativity, and geodesy. However, the challenge of verifying…

Radio-frequency electric-dipole transitions between nearly degenerate, opposite parity levels of atomic dysprosium (Dy) were monitored over an eight-month period to search for a variation in the fine-structure constant, $\alpha$. The data…

We compare the sensitivity of a recent bound on time variation of the fine structure constant from optical clocks with bounds on time varying fundamental constants from atomic clocks sensitive to the electron-to-proton mass ratio, from…

We performed accurate calculation of $\alpha$-dependence ($\alpha=e^2/hc$) of the transition frequencies for ions, which are used in a search for the variation of the fine structure constant $\alpha$ in space-time. We use Dirac-Hartree-Fock…

We calculate the sensitivity of the inversion spectrum of ammonia to possible time-variation of the ratio of the proton mass to the electron mass, mu=m_p/m_e. For the inversion transition (lambda= 1.25 cm^{-1}) the relative frequency shift…

In neutral atom optical clocks, the higher-order atomic polarizability terms lead to the clock transition frequency shift which is motion-state dependent and nonlinear with the optical lattice depth. We propose to use an auxiliary optical…

We report on an evaluation of an optical clock that uses the $\phantom{}^2S_{1/2} \rightarrow \phantom{}^2D_{5/2}$ transition of a single $^{88}$Sr$^+$ ion as the reference. In contrast to previous work, we estimate the effective…

Quantum corrections to the conductivity allow experimental assessment of electronic coherence in metals. We consider whether independent measurements of different corrections are quantitatively consistent, particularly in systems with…

Optical lattice clocks are the prospective devices that can probe many subtle physics including temporal variation of the fine structure constant ($\alpha_e$). These studies necessitate high-precision measurements of atomic clock frequency…

We present the quantum-mechanical calculations of the dimensionless sensitivity coefficients Q to small changes in the fundamental physical constant mu = m_e/m_p - the electron-to-proton mass ratio - for a number of low-frequency (1-50 GHz)…

Testing the spatial variation of fine-structure constant $\alpha$ indicated in [Webb et al., Phys. Rev. Lett. 107, 191101 (2011)] with terrestrial laboratory atomic measurements requires at least $\dot{\alpha}/\alpha \sim…

We compare the long-term fractional frequency variation of four hydrogen masers that are part of an ensemble of clocks comprising the National Institute of Standards and Technology,(NIST), Boulder, timescale with the fractional frequencies…

We performed an absolute frequency measurement of the $^1S_{0}$-$^3P_{0}$ transition in $^{87}$Sr with a fractional uncertainty of $1.2 \times 10^{-15}$, which is less than one third that of our previous measurement. A caesium fountain…

For electric quadrupole ($E2$) observables, which depend on the large-distance tails of the nuclear wave function, ab initio no-core configuration interaction (NCCI) calculations converge slowly, making meaningful predictions challenging to…

A new method for examining the possible space-time variation of the fine structure constant ($\alpha$) is proposed. The technique uses a relatively simple measurement with an optical resonator to compare atom-stabilized optical frequency…

Improvements in atom-light coherence are foundational to progress in quantum information science, quantum optics, and precision metrology. Optical atomic clocks require local oscillators with exceptional optical coherence due to the…