Equation of state and self-bound droplet in Rabi-coupled Bose mixtures

Laser induced transitions between internal states of atoms have been playing a fundamental role to manipulate atomic clouds for many decades. In absence of interactions each atom behaves independently and their coherent quantum dynamics is described by the Rabi model. Since the experimental observation of Bose condensation in dilute gases, static and dynamical properties of multicomponent quantum gases have been extensively investigated. Moreover, at very low temperatures quantum fluctuations crucially affect the equation of state of many-body systems. Here we study the effects of quantum fluctuations on a Rabi-coupled two-component Bose gas of interacting alkali atoms. The divergent zero-point energy of gapless and gapped elementary excitations of the uniform system is properly regularized obtaining a meaningful analytical expression for the beyond-mean-field equation of state. In the case of attractive inter-particle interaction we show that the quantum pressure arising from Gaussian fluctuations can prevent the collapse of the mixture with the creation of a self-bound droplet. We characterize the droplet phase and discover an energetic instability above a critical Rabi frequency provoking the evaporation of the droplet. Finally, we suggest an experiment to observe such quantum droplets using Rabi-coupled internal states of $^{39}$K atoms.Comment: to be published in Scientific Report

Lattice Yb Optical Clock and Cryogenic Cs Fountain at Inrim

In this paper we present the current status in the realization of a new generation of high accuracy frequency standards at INRIM, whose relative frequency uncertainty is expected to achieve and possibly pass the 10-16 range. Currently we are developing a nitrogen cooled cryogenic Cs fountain and a dipole trap neutral Yb optical clock. This development will allow us to make an absolute measurement of the Yb clock frequency against a primary frequency reference in the low 10-16 rang

Tracking DDS for Coherent Optical Links

We report on the design and the realization of a digital architecture based on a tracking direct digital synthesizer (DDS) driven by a Field Programmable Gate Array (FPGA) for the implementation of a coherent optical link for time and frequency dissemination. The realized digital system has been implemented and characterized on a real fiber link on a 47 km metropolitan optical telecommunication network using a Dense Wavelength Division Multiplexing, that is shared with the internet data traffic. We describe the technique, the hardware and the characterization of the link, and we compare the new digital system with the analogic one, that uses common fiber links electronics

The Cryogenic Fountain ITCsF2

This paper describes the new twin laser-cooled Cs fountain primary frequency standards NIST-F2 and IT-CsF2, and presents their most innovative design features. Most significant is a cryogenic microwave interrogation region which dramatically reduces the blackbody radiation shift. We present as well a preliminary accuracy evaluation of IT-CsF

Novel techniques for optical fiber links beyond current practice

It is well known that temperature variations and acoustic noise affect ultrastable frequency dissemination along optical fiber. Active stabilization techniques are in general adopted to compensate for the fiber-induced phase noise. However, despite this compensation, the ultimate link performances remain limited by the so called delay-unsuppressed fiber noise that is related to the propagation delay of the light in the fiber. In this paper, we demonstrate a data post-processing approach which enables us to overcome this limit. We implement a subtraction algorithm between the optical signal delivered at the remote link end and the round-trip signal. In this way, a 6dB improvement beyond the fundamental limit imposed by delay-unsuppressed noise is obtained. This result enhances the resolution of possible comparisons between remote optical clocks by a factor of 2. We confirm the theoretical prediction with experimental data obtained on a 47km metropolitan fiber link, and propose how to extend this method for frequency dissemination purposes as well

Optical frequency transfer with a 1284 km coherent fiber link

We realized a coherent optical fiber link in Italy, with a fiber haul of 642 km. To characterize the link, we doubled the link to 1284 km, demonstrating a characterization technique based on the double round trip on a single fiber. The link is intended to significantly improve the frequency references used in radio-astronomy and precision measurements in atomic physics. The data analysis is based on the Allan deviation, whose expression is theoretically derived from the noise power spectrum. The demonstrated resolution is 3x10-19 in 1000 s and the uncertainty of the transfer is 5x10-19. The arming of a second fiber is avoided, and this could be rather beneficial to long hauls realizations for a continental fiber network for frequency and time metrolog