arXiv subjects

P. H. Jones

Publications and source records attributed to P. H. Jones.

10 recordsLinked to original sources

arXiv2022

Roadmap for Optical Tweezers

Optical tweezers are tools made of light that enable contactless pushing, trapping, and manipulation of objects ranging from atoms to space light sails. Since the pioneering work by Arthur Ashkin in the 1970s, optical tweezers have evolved into sophisticated instruments and have been employed in a broad range of applications in life sciences, physics, and engineering. These include accurate force and torque measurement at the femtonewton level, microrheology of complex fluids, single micro- and nanoparticle spectroscopy, single-cell analysis, and statistical-physics experiments. This roadmap provides insights into current investigations involving optical forces and optical tweezers from their theoretical foundations to designs and setups. It also offers perspectives for applications to a wide range of research fields, from biophysics to space exploration.

physics.optics↗

arXiv2010

Brownian Motion of Graphene

We study the Brownian motion (BM) of optically trapped graphene flakes. These orient orthogonal to the light polarization, due to the optical constants anisotropy. We explain the flake dynamics, measure force and torque constants and derive a full electromagnetic theory of optical trapping. The understanding of two dimensional BM paves the way to light-controlled manipulation and all-optical sorting of biological membranes and anisotropic macromolecules.

cond-mat.mtrl-sci↗

arXiv2006

Directed motion for delta-kicked atoms with broken symmetries: comparison between theory and experiment

We report an experimental investigation of momentum diffusion in the delta-function kicked rotor where time symmetry is broken by a two-period kicking cycle and spatial symmetry by an alternating linear potential. We exploit this, and a technique involving a moving optical potential, to create an asymmetry in the momentum diffusion that is due to the classical chaotic diffusion. This represents a realization of a type of Hamiltonian quantum ratchet.

quant-ph↗

arXiv2005

Rectifying fluctuations in an optical lattice

We have realized a Brownian motor by using cold atoms in a dissipative optical lattice as a model system. In our experiment the optical potential is spatially symmetric and the time-symmetry of the system is broken by applying appropriate zero-mean ac forces. We identify a regime of rectification of forces and a regime of rectification of fluctuations, the latter corresponding to the realization of a Brownian motor.

cond-mat.stat-mech↗

arXiv2005

Resonant activation in a nonadiabatically driven optical lattice

We demonstrate the phenomenon of resonant activation in a non-adiabatically driven dissipative optical lattice with broken time-symmetry. The resonant activation results in a resonance as function of the driving frequency in the current of atoms through the periodic potential. We demonstrate that the resonance is produced by the interplay between deterministic driving and fluctuations, and we also show that by changing the frequency of the driving it is possible to control the direction of the diffusion.

cond-mat.stat-mech↗

arXiv2005

Asymmetric diffusion in the delta-kicked rotor with broken symmetries

We report an experimental investigation of momentum diffusion in the delta-function kicked rotor where time symmetry is broken by a two-period kicking cycle and spatial symmetry by an alternating linear potential. The momentum diffusion constant is thus modified by kick-to-kick correlations which show a momentum dependence. We exploit this, and a technique involving a moving optical potential, to create an asymmetry in the momentum diffusion that is due entirely to the chaotic dynamics.

physics.atom-ph↗

arXiv2004

Chaotic quantum ratchets and filters with cold atoms in optical lattices: properties of Floquet states

Recently, cesium atoms in optical lattices subjected to cycles of unequally-spaced pulses have been found to show interesting behavior: they represent the first experimental demonstration of a Hamiltonian ratchet mechanism, and they show strong variability of the Dynamical Localization lengths as a function of initial momentum. The behavior differs qualitatively from corresponding atomic systems pulsed with equal periods, which are a textbook implementation of a well-studied quantum chaos paradigm, the quantum delta-kicked particle (delta-QKP). We investigate here the properties of the corresponding eigenstates (Floquet states) in the parameter regime of the new experiments and compare them with those of the eigenstates of the delta-QKP at similar kicking strengths. We show that, with the properties of the Floquet states, we can shed light on the form of the observed ratchet current as well as variations in the Dynamical Localization length.

physics.atom-ph↗

arXiv2004

Atoms in double-delta-kicked periodic potentials: chaos with long-range correlations

We report an experimental and theoretical study of the dynamics of cold atoms subjected to closely-spaced pairs of pulses in an optical lattice. The experiments show the interplay between fully coherent quantum dynamics and a novel momentum-diffusion regime: for all previously-studied delta-kicked systems, chaotic classical dynamics shows diffusion with short-time (2 or 3-kick) correlations; here, chaotic diffusion combines with new types of long-ranged 'global' correlations, between all kick-pairs, which control transport through trapping regions in phase-space. Analytical formulae are presented and, with quantum localization, are used to analyse the experiments.

physics.atom-ph↗

arXiv2003

Shifting the boundaries: pulse-shape effects in the atom-optics kicked rotor

We present the results of experiments performed on cold caesium in a pulsed sinusoidal optical potential created by counter-propagating laser beams having a small frequency difference in the laboratory frame. Since the atoms, which have average velocity close to zero in the laboratory frame, have non-zero average velocity in the co-moving frame of the optical potential, we are able to centre the initial velocity distribution of the cloud at an arbitrary point in phase-space. In particular, we demonstrate the use of this technique to place the initial velocity distribution in a region of phase-space not accessible to previous experiments, namely beyond the momentum boundaries arising from the finite pulse duration of the potential. We further use the technique to explore the kicked rotor dynamics starting from a region of phase-space where there is a strong velocity dependence of the diffusion constant and quantum break time and demonstrate that this results in a marked asymmetry in the chaotic evolution of the atomic momentum distribution.

quant-ph↗

arXiv2000

Coherent transients in optical lattices

We use a method based on optical coherent transients to study the vibrational coherence lifetimes of atoms trapped in the potential wells of a near-resonant optical lattice in the oscillating regime. The dependence of the positions and widths of the vibrational Raman resonances of the coherent transient spectra on the intensity, detuning, and geometry of the lattice beams is investigated and the results are compared with theoretical predictions. It is shown that the principal source of broadening of the vibrational Raman resonances is the anharmonicity of the light-shift potential wells. We also perform time-resolved measurements of the vibrational excitation of atoms equilibrating in an optical lattice.

physics.atom-ph↗