arXiv subjects

Georgios Vasilakis

Publications and source records attributed to Georgios Vasilakis.

10 recordsLinked to original sources

arXiv2026

Nuclear slowing-down factors in alkali-metal vapors

Nuclear slowing-down factors account for the sharing of angular momentum between the electron and the nucleus in the effective Bloch description of alkali-metal spin dynamics in the spin-exchange-relaxation-free (SERF) regime. For collinear optical pumping and magnetic field, we find that longitudinal and transverse spin dynamics are characterized by different polarization-dependent slowing-down factors. Transverse dynamics are governed by the conventional factor $q(p)$, with $p$ the electron spin polarization, whereas longitudinal relaxation is governed by $q(p)+p\,dq(p)/dp$. The two factors coincide at zero polarization but differ substantially at high polarization, where the single-factor description overestimates the underlying pumping and relaxation rates inferred from longitudinal transients by factors approaching two to four, depending on the nuclear spin. We further derive closed-form expressions, valid at arbitrary polarization, for the residual spin-exchange relaxation of the transverse spin components at finite magnetic field along the pumping axis. This contribution is quadratic in the magnetic field and can become comparable to the zero-field linewidth at fields well within the SERF regime. The results are obtained by perturbation theory on the density-matrix dynamics linearized around the stationary state and are verified by numerical solutions of the microscopic density-matrix equation. These findings refine the effective Bloch description of alkali-metal spin dynamics and are directly relevant to atomic magnetometers and alkali-metal--noble-gas comagnetometers, including those used in precision searches for physics beyond the Standard Model.

physics.atom-ph↗

arXiv2025

Atomtronic Matter-Wave Optics

Matterwaves made up of ultra-cold quantum-degenerate atoms have enabled the creation of tools having unprecedented sensitivity and precision in measuring gravity, rotation or magnetic fields. Applications range from gravitational wave detection and tests of Einstein's equivalence principle to inertial sensing for navigation and gravitational gradient sensing for oil and mineral exploration. In this letter, we introduce atom-optics as a novel tool of manipulating matterwaves in ring-shaped coherent waveguides. We collimate and focus matterwaves derived from Bose-Einstein Condensates (BECs) and ultra-cold thermal atoms in ring-shaped time-averaged adiabatic potentials. We demonstrate `delta-kick cooling' of BECs, reducing their expansion energies by a factor of 34. The atomtronic waveguide ring has a radius of only $485\,\mu m$, compared to other state-of-the-art experiments requiring zero gravity or chambers of ten meter. This level of control with extremely reduced spatial requirements is an important step towards atomtronic quantum sensors.

quant-ph↗

arXiv2025

Precision Minimally-destructive detection of ultra-cold atomic ensembles

Over the last two decades the cold-atom physics has matured from proof-of-principle demonstrations to a versatile platform for precision measurements and study of quantum phenomena. Ultra-cold atomic ensembles have been used both for technological and fundamental science applications. To fully exploit their potential, a precise measurement and control of the atom number in the ensemble is crucial. We report on a precise, minimally-destructive measurement technique that can be used to prepare an atomic ensemble with a desired atom number. The measurement relies on the dispersive light-atom interaction, thus it is expected to have a negligible effect on the ensemble temperature and to induce minimal decoherence in the atomic quantum state. As a result, it can be used to perform quantum-enhanced measurements and prepare the atom-number state at the start of an interferometer sequence.

quant-ph↗

arXiv2021

A Nanosecond-Resolved Atomic Hydrogen Magnetometer

Spin polarized atomic ensembles can be used for the precise measurement of magnetic field. Conventional atomic magnetometers have demonstrated high sensitivities, albeit at low detection bandwidth, fundamentally limited by the Larmor precession frequency of the atoms. Here, we introduce a new type of atomic magnetometer which can realize sensitive detection with high temporal resolution. The magnetometer is based on monitoring the effect of the magnetic field on the hyperfine coherences of spin-polarized hydrogen atoms produced from the rapid photodissociation of hydrogen chloride (HCl). This scheme extends the magnetic measurement bandwidth to an upper frequency limit set by the hyperfine interaction. The use of HCl as the source for polarized atoms allows for large spin densities in the range of $10^{19}$ - $10^{20} cm^{-3}$, many orders of magnitude higher than those achieved with conventional alkali-atomic magnetometers. A spin-projection noise-limited magnetometer smaller than 100 μm can detect with nanosecond temporal resolution a magnetic field as low as 1 nT. This novel magnetometer opens new possibilities for precise measurement of ultrafast magnetic fields, with applications in biology, surface science and chemistry.

physics.atom-ph↗

arXiv2021

Magnetometry with spin polarized Hydrogen from molecular photo-dissociation

In a recent publication [arXiv:2010.14579], we introduced a new type of atomic magnetometer, which relies on hydrohalide photo-dissociation to create high-density spin-polarized hydrogen. Here, we extend our previous work and present a detailed theoretical analysis of the magnetometer signal and its dependence on time. We also derive the sensitivity for a spin-projection noise limited magnetometer, which can be applied to an arbitrary magnetic field waveform.

physics.atom-ph↗

arXiv2019

Hypersonic Bose-Einstein Condensates in Accelerator Rings

Some of the most sensitive and precise measurements to date are based on matterwave interferometry with freely falling atomic clouds. Examples include high-precision measurements of inertia, gravity and rotation. In order to achieve these very high sensitivities, the interrogation time has to be very long and consequently the experimental apparatus has to be very tall, in some cases reaching ten or even one hundred meters. Cancelling gravitational acceleration, e.g. in atomtronic circuits6,7 and matterwave guides, will result in compact devices having much extended interrogation times and thus much increased sensitivity both for fundamental and practical measurements. In this letter, we demonstrate extremely smooth and controllable matterwave guides by transporting Bose-Einstein condensates (BEC) over macroscopic distances: We use a novel neutral-atom accelerator ring to bring BECs to very high speeds (16x their velocity of sound) and transport them in a magnetic matterwave guide for 15 cm whilst fully preserving their internal coherence. The high angular momentum of more than 40000h per atom gives access to the higher Landau levels of quantum Hall states. The hypersonic velocities combined with our ability to control the potentials with pico-Kelvin precision open new perspectives in the study of superfluidity and give rise to new regimes of tunnelling and transport. Coherent matterwave guides are expected to enable interaction times of several seconds in highly compact devices. These developments will result in portable guided-atom interferometers for applications such as inertial navigation and gravity mapping.

quant-ph↗

arXiv2019

Simple precision measurements of optical beam sizes

We present a simple precision-method to quickly and accurately measure the diameters of Gaussian beams, Airy spots, and central peak of Bessel beams ranging from the sub-millimeter to many centimeters without specialized equipment. Simply moving a wire through the beam and recording the relative losses using an optical power meter, one can easily measure the beam diameters with a precision of 1%. The accuracy of this method has been experimentally verified for Gaussian beams down to the limit of a commercial slit-based beam profiler (3%).

physics.ins-det↗

arXiv2017

Quantum back action evading measurement of motion in a negative mass reference frame

Quantum mechanics dictates that a continuous measurement of the position of an object imposes a random back action perturbation on its momentum. This randomness translates with time into position uncertainty, thus leading to the well known uncertainty on the measurement of motion. Here we demonstrate that the quantum back action on a macroscopic mechanical oscillator measured in the reference frame of an atomic spin oscillator can be evaded. The collective quantum measurement on this novel hybrid system of two distant and disparate oscillators is performed with light. The mechanical oscillator is a drum mode of a millimeter size dielectric membrane and the spin oscillator is an atomic ensemble in a magnetic field. The spin oriented along the field corresponds to an energetically inverted spin population and realizes an effective negative mass oscillator, while the opposite orientation corresponds to a positive mass oscillator. The quantum back action is evaded in the negative mass setting and is enhanced in the positive mass case. The hybrid quantum system presented here paves the road to entanglement generation and distant quantum communication between mechanical and spin systems and to sensing of force, motion and gravity beyond the standard quantum limit.

quant-ph↗

arXiv2016

Non-invasive detection of animal nerve impulses with an atomic magnetometer operating near quantum limited sensitivity

Magnetic fields generated by human and animal organs, such as the heart, brain and nervous system carry information useful for biological and medical purposes. These magnetic fields are most commonly detected using cryogenically-cooled superconducting magnetometers. Here we present the frst detection of action potentials from an animal nerve using an optical atomic magnetometer. Using an optimal design we are able to achieve the sensitivity dominated by the quantum shot noise of light and quantum projection noise of atomic spins. Such sensitivity allows us to measure the nerve impulse with a miniature room-temperature sensor which is a critical advantage for biomedical applications. Positioning the sensor at a distance of a few millimeters from the nerve, corresponding to the distance between the skin and nerves in biological studies, we detect the magnetic field generated by an action potential of a frog sciatic nerve. From the magnetic field measurements we determine the activity of the nerve and the temporal shape of the nerve impulse. This work opens new ways towards implementing optical magnetometers as practical devices for medical diagnostics.

quant-ph↗

arXiv2014

Generation of a squeezed state of an oscillator by stroboscopic back-action-evading measurement

Continuous observation on an oscillator is known to result in quantum back-action which limits the knowledge acquired by the measurement. A careful balance between the information obtained and the back-action disturbance leads to a limit known as the standard quantum limit. The means to surpass this limit by modulating the measurement strength with the period proportional to half period of the oscillation has been proposed decades ago (Braginskii et al 1978 JETP Lett. 27 276; Thorne et al 1978 Phys. Rev. Lett. 40 667; Braginskii et al 1980 Science 209 547). Such modulated or stroboscopic observation leading to a squeezed state of one quadrature of the oscillator motion with the quantum noise below that of the zero-point fluctuations has been a long-standing goal. Here, we report on the generation of a quadrature-squeezed state of an oscillator by stroboscopic back-action evading measurement. The oscillator is the collective spin of an atomic ensemble precessing in magnetic field. It is initially prepared in nearly the ground state with an average thermal occupancy number $0.08 \pm 0.01$. The oscillator is coupled to the optical mode of a cavity, and the cavity output field detected with polarization homodyning serves as the meter. A back-action-evading measurement is performed by stroboscopically modulating the intensity of the light field at twice the Larmor frequency, resulting in a squeezed state conditioned on the light-polarization measurement with $2.2 \pm 0.3$ dB noise reduction below the zero-point fluctuations for the measured quadrature. The demonstrated squeezing holds promise for metrological advantage in quantum sensing.

quant-ph↗