CyberSec Research

We report a single-ion optical atomic clock with fractional frequency uncertainty of $5.5\times10^{-19}$ and fractional frequency stability of $3.5 \times10^{-16}/\sqrt{\tau/\mathrm{s}}$, based on quantum logic spectroscopy of a single $^{27}$Al$^+$ ion. A co-trapped $^{25}$Mg$^+$ ion provides sympathetic cooling and quantum logic readout of the $^{27}$Al$^+$ $^1$S$_0\leftrightarrow^3$P$_0$ clock transition. A Rabi probe duration of 1 s, enabled by laser stability transfer from a remote cryogenic silicon cavity across a 3.6 km fiber link, results in a threefold reduction in instability compared to previous $^{27}$Al$^+$ clocks. Systematic uncertainties are lower due to an improved ion trap electrical design, which reduces excess micromotion, and a new vacuum system, which reduces collisional shifts. We also perform a direction-sensitive measurement of the ac magnetic field due to the RF ion trap, eliminating systematic uncertainty due to field orientation.

Disordered potentials fundamentally alter the transport properties and coherence of quantum systems. They give rise to phenomena such as Anderson localization in non-interacting systems, inhibiting transport. When interactions are introduced, the interplay with disorder becomes significantly more complex, and the conditions under which localization can be observed remain an open question. In interacting bosonic systems, a Bose glass is expected to emerge at low energies as an insulating yet compressible state without long-range phase coherence. While originally predicted to occur as a ground-state phase, more recent studies indicate that it exists at finite temperature. A key open challenge has been the direct observation of reduced phase coherence in the Bose-glass regime. In this study, we utilize ultracold bosonic atoms in a quantum-gas microscope to probe the emergence of the Bose-glass phase in a two-dimensional square lattice with a site-resolved, reproducible disordered potential. We identify the phase through in-situ distribution and particle fluctuations, via a local measurement of the Edwards-Anderson parameter. To measure the short-range phase coherence in the Bose glass, we employ Talbot interferometry in combination with single-atom-resolved detection. Finally, by driving the system in and out of the Bose-glass phase, we observe signatures for non-ergodic behavior.

We present a theoretical analysis of Beat-Note Superlattices (BNSLs), a recently demonstrated technique for generating periodic trapping potentials for ultracold atomic clouds, with arbitrarily large lattice spacings while maintaining interferometric stability. By combining two optical lattices with slightly different wavelengths, a beatnote intensity pattern is formed, generating, for low depths, an effective lattice potential with a periodicity equal to the wavelength associated to the difference between the wavevectors of the two lattices. We study the range of lattice depths and wavelengths under which this approximation is valid and investigate its robustness against perturbations. We present a few examples where the use of BNSLs could offer significant advantages in comparison to well established techniques for the manipulation of ultracold atomic gases. Our results highlight the potential of BNSLs for quantum simulation, atom interferometry, and other applications in quantum technologies.

We implement in-situ mid-circuit measurement and reset (MCMR) operations on a trapped-ion quantum computing system by using metastable qubit states in $^{171}\textrm{Yb}^+$ ions. We introduce and compare two methods for isolating data qubits from measured qubits: one shelves the data qubit into the metastable state and the other drives the measured qubit to the metastable state without disturbing the other qubits. We experimentally demonstrate both methods on a crystal of two $^{171}\textrm{Yb}^+$ ions using both the $S_{1/2}$ ground state hyperfine clock qubit and the $S_{1/2}$-$D_{3/2}$ optical qubit. These MCMR methods result in errors on the data qubit of about $2\%$ without degrading the measurement fidelity. With straightforward reductions in laser noise, these errors can be suppressed to less than $0.1\%$. The demonstrated method allows MCMR to be performed in a single-species ion chain without shuttling or additional qubit-addressing optics, greatly simplifying the architecture.

Mid-circuit measurement and reset of subsets of qubits is a crucial ingredient of quantum error correction and many quantum information applications. Measurement of atomic qubits is accomplished through resonant fluorescence, which typically disturbs neighboring atoms due to photon scattering. We propose and prototype a new scheme for measurement that provides both spatial and spectral isolation by using tightly-focused individual laser beams and narrow atomic transitions. The unique advantage of this scheme is that all operations are applied exclusively to the read-out qubit, with negligible disturbance to the other qubits of the same species and little overhead. In this letter, we pave the way for non-invasive and high fidelity mid-circuit measurement and demonstrate all key building blocks on a single trapped barium ion.

We demonstrate structured illumination super-resolution imaging in the Terahertz (THz) frequency band using the Virtually Structured Detection (VSD) method. Leveraging our previously reported high-speed, high-sensitivity atomic-based THz imager, we achieve a resolution enhancement of 74(3)% at 0.55 THz, without the aid of deconvolution methods. We show a high-speed THz imaging system is compatible with the use of advanced optical techniques, with potential disruptive effects on applications requiring both high speed and high spatial resolution imaging in the THz range.

Quantum electrodynamics predicts identity of incident and emitted photons in stimulated emission. This fundamental law is important to test experimentally. In this work stimulated emission in GaAs semiconductor amplifier was investigated and positive frequency shift of the amplified beam was detected. In relative units this frequency shift was found equal $\Delta\nu/\nu = (+1.7 \pm 0.2)\cdot10^{-18}$. This indicates violation of the photon energy conservation in stimulated emission.

Within the framework of the theory of irreducible tensor operators, using well-known general analytical results for double sums ($\sum_{jm}$) of products of two $3j$-Wigner symbols, analytical expressions for single sums ($\sum_m$) for the values $j_1 = j_2 = 1$ and $j = 2$ parameters of the upper row $3j$-Wigner symbol are specified. The expressions obtained supplement the well-known analytical results of the theory of angular momentum and are in demand in solving, in particular, such problems of atomic physics as the construction of a nonrelativistic quantum theory of single and double bremsstrahlung when a photon is scattered by an atom (atomic ion) (Hopersky et al [6,7,8]) and two-photon resonance single ionization of the deep shell of an atomic ion (Hopersky et al [9]).

We demonstrate nuclear magnetic resonance of optically trapped ground-state ultracold 87Sr atoms. Using a scheme in which a cloud of ultracold 87Rb is co-trapped nearby, we improve the determination of the nuclear g factor, gI , of atomic 87Sr by more than two orders of magnitude, reaching accuracy at the parts-per-million level. We achieve similar accuracy in the ratio of relevant g factors between Rb and Sr. This establishes ultracold 87Sr as an excellent linear in-vacuum magnetometer. These results are relevant for ongoing efforts towards quantum simulation, quantum computation and optical atomic clocks employing 87Sr, and these methods can also be applied to other alkaline-earth and alkaline-earth-like atoms.

Mendeleev's periodic table successfully groups atomic elements according to their chemical and spectroscopic properties. However, it becomes less sufficient in describing the electronic properties of highly charged ions (HCIs) in which many of the outermost electrons are ionized. In this work, we put forward a periodic table particularly suitable for HCIs. It is constructed purely based on the successive electron occupation of relativistic orbitals. While providing a much-simplified description of the level structure of highly charged isoelectronic ions -- essential for laboratory and astrophysical plasma spectroscopies, such a periodic table predicts a large family of highly forbidden transitions suitable for the development of next-generation optical atomic clocks. Furthermore, we also identify universal linear $Z$ scaling laws ($Z$ is the nuclear charge) in the so-called ``Coulomb splittings'' between angular momentum multiplets along isoelectronic sequences, complementing the physics of electron-electron interactions in multielectron atomic systems.

Harnessing the potential of quantum sensors to assist in navigation requires enabling their operation in complex, dynamic environments and integrating them within existing navigation systems. While cross-couplings from platform dynamics generally degrade quantum measurements in a complex manner, navigation filters would need to be designed to handle such complex quantum sensor data. In this work, we report on the realization of a high-fidelity model of an atom-interferometry-based gravity gradiometer and demonstrate its integration with a map-matching navigation filter. Relying on the ability of our model to simulate the sensor behaviour across various dynamic platform environments, we show that aiding navigation via map matching using quantum gravity gradiometry results in stable trajectories, and highlight the importance of non-Gaussian errors arising from platform dynamics as a key challenge to map-matching navigation. We derive requirements for mitigating these errors, such as maintaining sensor tilt below 3.3 degrees, to inform future sensor development priorities. This work demonstrates the value of an end-to-end approach that could support future optimization of the overall navigation system. Beyond navigation, our atom interferometer modelling framework could be relevant to current research and innovation endeavours with quantum gravimeters, gradiometers and inertial sensors.

Modern experiments in quantum metrology, sensing, and quantum computing require precise control of the state of atoms and molecules, achieved through the use of highly stable lasers and microwave generators with low phase noise. One of the most effective methods for ensuring high frequency stability is stabilization using a high-finesse Fabry-P\'erot reference cavity. However, implementing separate stabilization systems for each laser increases the complexity and size of the setup, limiting its use to laboratory conditions. An alternative approach is the use of a femtosecond optical frequency comb, which transfers the noise characteristics of a single stabilized frequency reference to other wavelengths in the optical and microwave ranges. In this work, we demonstrate a scheme for transferring frequency stability from an ultrastable laser at 871 nm to a laser at 1550 nm. Measurements using the three-cornered hat method show that the stabilized laser exhibits a fractional frequency instability of less than 4e-15 for averaging times between 0.4 and 2 s, and below 1e-14 for intervals ranging from 0.2 to 500 s. The femtosecond optical frequency comb and the cavity-stabilized laser were designed to meet compactness and portability requirements to enable field and onboard applications.

This work presents a perturbative calculation methodology for evaluating the energy shifts and broadening of vibrational energy levels, caused by interactions between bound and unbound dissociative electronic states. The method is validated against previously semiclassical analyzed cases, demonstrating remarkable consistency. We successfully applied this approach to the N$_2$ molecule, which exhibits a strong spin-orbit interaction between the bound C$''^5\Pi_u$ and the repulsive 1$^7\Sigma^+_u$ electronic states, around 36 cm$^{-1}$. This interaction constitutes an major pathway for N($^{2}$D) production, important in both excitation and quenching in plasma afterglows. As a result, the maximum absolute shift of 0.15 cm$^{-1}$ was found for the C$''^5\Pi_u$ ($v$ = 7) and maximum broadening of 0.45 cm$^{-1}$ was calculated for $v$ = 8, demonstrating significant perturbation of the C$''^5\Pi_u$ by the 1$^7\Sigma^+_u$ state. The results obtained were compared with direct calculations of the predissociation rates of the C$''^5\Pi_u$ bound state, showing very good agreement.

The recombination of halogen atoms has been a research topic in chemical physics for over a century. All theoretical descriptions of atom recombination depend on a two-step assumption, where two colliding atoms first form an unstable complex before a third colliding body either relaxes or reacts with it to yield a diatomic molecule. These mechanisms have served well in describing some of the dynamics of atom recombination, but have not yet provided a full theoretical understanding. In this work, we consider the role of the direct three-body recombination mechanism in halogen recombination reactions X + X + M $\rightarrow$ X$_2$ + M, where X is a halogen atom, and M is a rare gas atom. Our results agree well with experimental bromide and iodine recombination measurements, demonstrating that direct three-body recombination is essential in halogen recombination reactions.

Investigating $K$-shell hollow atom spectra enhances our understanding of femtosecond phenomena in atomic physics, chemistry, and biology. Synchrotron measurements of two-electron one-photon (TEOP) transitions in low-$Z$ atoms have revealed discrepancies between experimental results and theoretical predictions of TEOP relative intensities. These discrepancies appear to originate from an incomplete description of an atom's response to the strong perturbation caused by $K$-shell double photoionization (DPI). The multiconfiguration Dirac-Hartree-Fock relativistic configuration interaction method has been applied for studying the TEOP spectra of Mg, Al, Si, S, Ar, and Ca atoms. The results show that branching ratios can be accurately reproduced by accounting for the effects of core and valence electron correlations, as well as the outer-shell ionization and excitation processes following $K$-shell DPI.

Rydberg atoms in static electric fields possess permanent dipole moments. When the atoms are close to a surface producing an inhomogeneous electric field, such as by the adsorbates on an atom chip, depending on the sign of the dipole moment of the Rydberg-Stark eigenstate, the atoms may experience a force towards or away from the surface. We show that by applying a bias electric field and coupling a desired Rydberg state by a microwave field of proper frequency to another Rydberg state with opposite sign of the dipole moment, we can create a trapping potential for the atom at a prescribed distance from the surface. Perfectly overlapping trapping potentials for several Rydberg states can also be created by multi-component microwave fields. A pair of such trapped Rydberg states of an atom can represent a qubit. Finally, we discuss an optimal realization of the swap gate between pairs of such atomic Rydberg qubits separated by a large distance but interacting with a common mode of a planar microwave resonator at finite temperature.

The Hartree-Fock-Rothaan equations are solved for He-like ions using the iterative self-consistent method. Bagci-Hoggan complete and orthonormal sets of exponential-type orbitals are employed as the basis. These orbitals satisfy the orthonormality relationship for quantum numbers with fractional order. They are solution of Schrodinger-like differential equation derived by the author. In a recent study conducted for the calculation of the hydrogen atom energy levels, it has been demonstrated that the fractional formalism of the principal and the angular momentum quantum numbers converges to the 1s level of the ground state energy of hydrogen atom, obtained from the solution of the standard Schrodinger equation. This study examines the effect of fractional values of the quantum numbers for two-electron systems, where electron correlation effects exist.

Determining the peak photon emission time and rate for an ensemble of $N$ quantum systems undergoing collective superradiant decay typically requires tracking the time evolution of the density operator, a process with computational costs scaling exponentially with $N$. We present compact, analytic formulas for evaluating the peak emission rate and time for initially fully excited quantum emitter ensembles, valid for any geometric configuration and emitter type. These formulas rely solely on the variance of the eigenvalues of a real symmetric $N \times N$ matrix, which describes collective dissipation. We demonstrate the versatility of these results across various environments, including free space, solid-state, and waveguide reservoirs. For large $N$ the formulas simplify further to depend on just two parameters: average nearest-neighbor spacing and emitter number. Finally, we present scaling laws and bounds on the spatial size of emitter ensembles, such that superradiance is maintained, independent of emitter number or density.