Physics

Using a spectrally resolved electron interferometry technique, we measure photoionization time delays between the 3s and 3p subshells of argon over a large 34-eV energy range covering the Cooper minima in both subshells. The observed strong variations of the 3s−3p delay difference, including a sign change, are well reproduced by theoretical calculations using the Two-Photon Two-Color Random Phase Approximation with Exchange. Strong shake-up channels lead to photoelectrons spectrally overlapping with those emitted from the 3s subshell. These channels need to be included in our analysis to reproduce the experimental data. Our measurements provide a stringent test for multielectronic theoretical models aiming at an accurate description of inter-channel correlation.

We present designs for the augmentation 'mirror' pulses of large-momentum-transfer atom interferometers that maintain their fidelity as the wavepacket momentum difference is increased. These bi-selective pulses, tailored using optimal control methods to the evolving bi-modal momentum distribution, should allow greater interferometer areas and hence increased inertial measurement sensitivity, without requiring elevated Rabi frequencies or extended frequency chirps. Using an experimentally validated model, we have simulated the application of our pulse designs to large-momentum-transfer atom interferometry using stimulated Raman transitions in a laser-cooled atomic sample of 85 Rb at 1 μ K. After the wavepackets have separated by 42 photon recoil momenta, our pulses maintain a fringe contrast of 90% whereas, for adiabatic rapid passage and conventional π pulses, the contrast is less than 10%. Furthermore, we show how these pulses may be adapted to suppress the detrimental off-resonant excitation that limits other broadband pulse schemes.

Precision measurements of quantum systems often seek to probe or must account for the interaction with blackbody radiation. Over the past several decades, much attention has been given to AC Stark shifts and stimulated state transfer. For a blackbody in thermodynamic equilibrium, these two effects are determined by the expectation value of photon number in each mode of the Planck spectrum. Here, we explore how the photon number variance of an equilibrium blackbody generally leads to a parametric broadening of the energy levels of quantum systems that is inversely proportional to the square-root of the blackbody volume. We consider the the effect in two cases which are potentially highly sensitive to this broadening: Rydberg atoms and atomic clocks. We find that even in blackbody volumes as small as 1\,cm 3 , this effect is unlikely to contribute meaningfully to transition linewidths.

We present the generation of high order harmonics in crystalline silicon subjected to intense near-infrared 30fs laser pulse. The harmonic spectrum extends from the near infrared to the extreme ultraviolet spectral region. Depending on the pulsed laser intensity, we distinguish two regimes of harmonic generation: (i) perturbative regime: electron-hole pairs born during each half-cycle of the laser pulse via multiphoton and tunnel transitions are accelerated in the laser electric field and gain kinetic energy; the electron-hole pairs then recombine in the ground state by emitting a single high-energy photon. The resultant high harmonic spectrum consists of sharp peaks at odd harmonic orders. (ii) non-perturbative regime: the intensity of the harmonics increases, their spectral width broadens and the position of harmonics shifts to shorter wavelengths. The blueshift of high harmonics in silicon are independent on the harmonic order which may be helpful in the design of continuously tunable XUV sources.

Branching fractions for decays from the P 3/2 level in 138 Ba + have been measured with a single laser-cooled ion. Decay probabilities to S 1/2 , D 3/2 and D 5/2 are determined to be 0.741716(71) , 0.028031(23) and 0.230253(61) , respectively, which are an order of magnitude improvement over previous results. Our methodology only involves optical pumping and state detection, and is hence relatively free of systematic effects. Measurements are carried out in two different ways to check for consistency. Our analysis also includes a measurement of the D 5/2 lifetime, for which we obtain 30.14(40)\,s.

We demonstrate a cryogenic buffer gas-cooled molecular beam source capable of producing bright, continuous beams of cold and slow free radicals via laser ablation over durations of up to 60~seconds. The source design uses a closed liquid helium reservoir as a large thermal mass to minimize heating and ensure reproducible beam properties during operation. Under typical conditions, the source produces beams of our test species SrF, containing 5× 10 12 molecules per steradian per second in the X 2 Σ(v=0,N=1) state with a rotational temperature of 1.0(2) K and a forward velocity of 140 m/s. The beam properties are robust and unchanged for multiple cell geometries but depend critically on the helium buffer gas flow rate, which must be ≥10 standard cubic centimeters per minute to produce bright, continuous beams of molecules for an ablation repetition rate of 55 Hz.

Quantum memories, devices that can store and retrieve photonic quantum states on demand, are essential components for scalable quantum technologies. It is desirable to push the memory towards the broadband regime in order to increase the data rate. Here, we present a theoretical and experimental study on the broadband optical memory based on electromagnetically-induced-transparency (EIT) protocol. We first provide a theoretical analysis on the issues and requirements to achieve a broadband EIT memory. We then present our experimental efforts on EIT memory in cold atoms towards the broadband or short-pulse regime. A storage efficiency of ~ 80 % with a pulse duration of 30 ns (corresponding to a bandwidth of 14.7 MHz) is realized. Limited by the available intensity of the control beam, we could not conduct an optimal storage for the even shorter pulses but still obtain an efficiency of larger than 50 % with a pulse duration of 14 ns (31.4 MHz). The achieved time-bandwidth-product at the efficiency of 50 % is 1267.

In the recent work [A.~Yamaguchi et. al, Phys. Rev. Lett. {\bf 123}, 113201 (2019)] Cd has been identified as an excellent candidate for a lattice clock. Here, we carried out computations needed for further clock development and made an assessment of the higher-order corrections to the light shift of the 5 s 2 1 S 0 -- 5s5p 3 P o 0 clock transition. We carried out calculations of the magnetic dipole and electric quadrupole polarizabilities and linear and circular hyperpolarizabilities of the 5 s 2 1 S 0 and 5s5p 3 P o 0 clock states at the magic wavelength and estimated uncertainties of these quantities. We also evaluated the second-order Zeeman clock transition frequency shift.

The precision measurements of the ratio of hyperfine structure constants for s 1/2 and p 1/2 states allow us to estimate the difference between hyperfine magnetic anomalies for these levels. We calculate the atomic factor in order to recover the absolute values of the hyperfine magnetic anomalies from their difference. Taking into account the hyperfine anomaly correction allows one to increase the accuracy of determining the g-factors of short-lived isotopes by more than an order of magnitude.

Modern spectroscopic experiments in few-electron atoms reached the level of precision at which an accurate description of quantum electrodynamics (QED) effects is mandatory. In many cases, theoretical treatment of QED effects has to be performed without any expansion in the nuclear binding strength parameter Zα (where Z is the nuclear charge number and α is the fine-structure constant). Such calculations involve multiple summations over the whole spectrum of the Dirac equation in the presence of the binding nuclear field, which can be evaluated in terms of the Dirac Green function. In this paper we describe the technique of numerical calculations of QED corrections with the Dirac Green function, developed in numerous investigations during the last two decades.