Filippo Levi

Direct Observation of Coherent Interorbital Spin-Exchange Dynamics

We report on the first direct observation of fast spin-exchange coherent oscillations between different long-lived electronic orbitals of ultracold 173Yb fermions. We measure, in a model-independent way, the strength of the exchange interaction driving this coherent process. This observation allows us to retrieve important information on the interorbital collisional properties of 173Yb atoms and paves the way to novel quantum simulations of paradigmatic models of two-orbital quantum magnetism.

Accuracy evaluation of NIST-F1

The evaluation procedure of a new laser-cooled caesium fountain primary frequency standard developed at the National Institute of Standards and Technology (NIST) is described. The new standard, NIST-F1, is described in some detail and typical operational parameters are discussed. Systematic frequency biases for which corrections are made - second-order Zeeman shift, black-body radiation shift, gravitational red shift and spin-exchange shift - are discussed in detail. Numerous other frequency shifts are evaluated, but are so small in this type of standard that corrections are not made for their effects. We also discuss comparisons of this standard both with local frequency standards and with standards at other national laboratories.

Double-pass acousto-optic modulator system

A practical problem that arises when using acousto-optic modulators (AOMs) to scan the laser frequency is the dependence of the beam diffraction angle on the modulation frequency. Alignment problems with AOM-modulated laser beams can be effectively eliminated by using the AOM in the double-pass configuration, which compensates for beam deflections. On a second pass through the AOM, the beam with its polarization rotated by 90° is deflected back such that it counterpropagates the incident laser beam and it can be separated from the input beam with a polarizing beam splitter. Here we present our design for a compact, stable, double-pass AOM with 75% double-pass diffraction efficiency and a tuning bandwidth of 68 MHz full width at half maximum for light transmitted through a single-mode fiber. The overall efficiency of the system (defined as the optical power out of the single-mode fiber divided by the optical power into the apparatus) is 60%.

First accuracy evaluation of NIST-F2

We report the first accuracy evaluation of NIST-F2, a second-generation laser-cooled caesium fountain primary standard developed at the National Institute of Standards and Technology (NIST) with a cryogenic (liquid nitrogen) microwave cavity and flight region. The 80?K atom interrogation environment reduces the uncertainty due to the blackbody radiation shift by more than a factor of 50. Also, the Ramsey microwave cavity exhibits a high quality factor (>50?000) at this low temperature, resulting in a reduced distributed cavity phase shift. NIST-F2 has undergone many tests and improvements since we first began operation in 2008. In the last few years NIST-F2 has been compared against a NIST maser time scale and NIST-F1 (the US primary frequency standard) as part of in-house accuracy evaluations. We report the results of nine in-house comparisons since 2010 with a focus on the most recent accuracy evaluation. This paper discusses the design of the physics package, the laser and optics systems and the accuracy evaluation methods. The type B fractional uncertainty of NIST-F2 is shown to be 0.11???10?15 and is dominated by microwave amplitude dependent effects. The most recent evaluation (August 2013) had a statistical (type A) fractional uncertainty of 0.44???10?15.

Planar-waveguide external cavity laser stabilization for an optical link with 10 -19 frequency stability

We stabilized the frequency of a compact planar-waveguide external cavity laser (ECL) on a Fabry-Perot cavity (FPC) through a Pound-Drever-Hall scheme. The residual frequency stability of the ECL is 10-14, comparable to the stability achievable with a fiber laser (FL) locked to an FPC through the same scheme. We set up an optical link of 100 km, based on fiber spools, that reaches 10-19 relative stability, and we show that its performances using the ECL or FL are comparable. Thus ECLs could serve as an excellent replacement for FLs in optical links where cost-effectiveness and robustness are important considerations.

Accuracy evaluation of ITCsF2: a nitrogen cooled caesium fountain

For almost two decades, caesium fountain primary frequency standards (PFS) have represented the best realization of the definition of the second in the International System of units. Their accuracy has progressively improved with time, reaching a few parts in 10 16 .I n this paper, we present the accuracy evaluation of ITCsF2, the new Cs fountain PFS developed at the Italian National Metrological Institute, designed to be operated at cryogenic temperature to reduce the blackbody radiation shift. The short-term stability of the ITCsF2 fountain is 2 × 10 −13 τ −1/2 when operated at high atomic density, and the relative inaccuracy reaches 2.3 × 10 −16 . We also report four calibrations of International Atomic Time with a relative frequency agreement of (−1.7 ± 3.2) × 10 −16 , between ITCsF2 and the average of the other

The light shift effect in the coherent population trapping cesium maser

The light shift, as observed in the coherent population trapping (CPT) maser, was investigated theoretically and experimentally. It was found that the light shift originates from the various sidebands that are present in the spectrum of the frequency-modulated laser used to observe the CPT phenomenon.

Frequency transfer via a two-way optical phase comparison on a multiplexed fiber network

We performed a two-way remote optical phase comparison on optical fiber. Two optical frequency signals were launched in opposite directions in an optical fiber and their phases were simultaneously measured at the other end. In this technique, the fiber noise is passively canceled, and we compared two optical frequencies at the ultimate 10(-21) stability level. The experiment was performed on a 47 km fiber that is part of the metropolitan network for Internet traffic. The technique relies on the synchronous measurement of the optical phases at the two ends of the link, which is here performed by digital electronics. This scheme offers some advantages with respect to active noise cancellation schemes, as the light travels only once in the fiber.

Yellow solid state laser for metrological applications

We present laser results obtained from a Dy³⁺-Tb³⁺ co-doped LiLuF₄ crystal, pumped by a blue emitting InGaN laser diode, aiming for generation of a compact 578 nm source. We exploit the yellow Dy³⁺ transition ⁴F(9/2)⇒⁶H(13/2) to generate yellow laser emission. The lifetime of the lower laser level is quenched, via energy transfer, to co-doped Tb³⁺ ions in the fluoride crystal. We report the growth technique, spectroscopic study, and room temperature continuous wave laser results in a hemispherical cavity at 574 nm, and with a highly reflective output coupler at 578 nm. A yellow laser at 578 nm is very relevant for metrological applications, in particular for pumping of the forbidden ¹S₀-³P₀ ytterbium clock transition, which is recommended as a secondary representation of the second in the international system of units.We present a blue diode pumped solid-state laser results of Dy3+-Tb3+ co-doped in LiLuF4 host crystal. We exploit the yellow Dy3+ transition between 4F9/2 ??? 6H13/2 energy levels, pumping with an InGaN laser diode. The lifetime of lower laser level is quenched via energy migrations, co-doping the fluoride crystal with Tb3+ ions. We also report the growth technique and the room temperature continuous wave (CW) laser results in a two mirrors cavity. This yellow laser at 578 nm is very relevant for metrological applications.y, in particular it corresponds to the forbidden 1S0->3P0 Ytterbium clock transition which will be used in the next generation optical clocks developed at INRiM, the Italian institute for metrology.

Realization of an ultrastable 578-nm laser for an Yb lattice clock

In this paper, we describe the development of an ultrastable laser source at 578 nm, realized using frequency sum generation. This source will be used to excite the clock transition ¹S₀ → ³P₀ in an ytterbium optical lattice clock experiment. Two independent ultrastable lasers have been realized, and the laser frequency noise and stability have been characterized.