arXiv subjects

R. E. Scholten

Publications and source records attributed to R. E. Scholten.

7 recordsLinked to original sources

arXiv2020

Interplay between geometric and dynamic phases in a single spin system

We use a combination of microwave fields and free precession to drive the spin of a nitrogen-vacancy (NV) center in diamond on different trajectories on the Bloch sphere, and investigate the physical significance of the frame-dependent decomposition of the total phase into geometric and dynamic parts. The experiments are performed on a two-level subspace of the spin-1 ground state of the NV, where the Aharonov-Anandan geometric phase manifests itself as a global phase, and we use the third level of the NV ground state triplet to detect it. We show that while the geometric Aharonov-Anandan phase retains its connection to the solid angle swept out by the evolving spin, it is generally accompanied by a dynamic phase that suppresses the geometric dependence of the system dynamics. These results offer insights into the physical significance of frame-dependent geometric phases.

quant-ph↗

arXiv2018

$T_2$-limited sensing of static magnetic fields via fast rotation of quantum spins

Diamond-based quantum magnetometers are more sensitive to oscillating (AC) magnetic fields than static (DC) fields because the crystal impurity-induced ensemble dephasing time $T_2^*$, the relevant sensing time for a DC field, is much shorter than the spin coherence time $T_2$, which determines the sensitivity to AC fields. Here we demonstrate measurement of DC magnetic fields using a physically rotating ensemble of nitrogen-vacancy centres at a precision ultimately limited by $T_2$ rather than $T_2^*$. The rotation period of the diamond is comparable to $T_2$ and the angle between the NV axis and the target magnetic field changes as a function of time, thus upconverting the static magnetic field to an oscillating field in the physically rotating frame. Using spin-echo interferometry of the rotating NV centres, we are able to perform measurements for over a hundred times longer compared to a conventional Ramsey experiment. With modifications our scheme could realise DC sensitivities equivalent to demonstrated NV center AC magnetic field sensitivities of order $0.1$\,nT\,Hz$^{-1/2}$.

quant-ph↗

arXiv2017

Magnetic pseudo-fields in a rotating electron-nuclear spin system

A precessing spin observed in a rotating frame of reference appears frequency-shifted, an effect analogous to the precession of a Foucault pendulum observed on the rotating Earth. This frequency shift can be understood as arising from a magnetic pseudo-field in the rotating frame that nevertheless has physically significant consequences, such as the Barnett effect. Detecting these pseudo-fields is experimentally challenging, as a rotating-frame sensor is required. Previous work has realised classical rotating-frame detectors. Here we use quantum sensors, nitrogen-vacancy (NV) centres, in a rapidly rotating diamond to detect pseudo-fields in the rotating frame. While conventional magnetic fields induce precession at a rate proportional to the gyromagnetic ratio, rotation shifts the precession of all spins equally, and thus primarily affect nearby $^{13}$C nuclear spins. We are thus able to explore these effects via quantum sensing in a rapidly rotating frame, and define a new approach to quantum control using rotationally-induced nuclear spin-selective magnetic fields. This work provides an integral step towards realising precision rotation sensing and quantum spin gyroscopes.

quant-ph↗

arXiv2016

Stimulated Raman Adiabatic Passage for Improved Performance of a Cold Atom Electron and Ion Source

We implement high-efficiency coherent excitation to a Rydberg state using stimulated Raman adiabatic passage in a cold atom electron and ion source. We achieve an efficiency of 60% averaged over the laser excitation volume with a peak efficiency of 82%, a 1.6 times improvement relative to incoherent pulsed-laser excitation. Using pulsed electric field ionization of the Rydberg atoms we create electron bunches with durations of 250 ps. High-efficiency excitation will increase source brightness, crucial for ultrafast electron diffraction experiments, and coherent excitation to high-lying Rydberg states could allow for the reduction of internal bunch heating and the creation of a high-speed single ion source.

physics.atom-ph↗

arXiv2012

Ambient Nanoscale Sensing with Single Spins Using Quantum Decoherence

Magnetic resonance detection is one of the most important tools used in life-sciences today. However, as the technique detects the magnetization of large ensembles of spins it is fundamentally limited in spatial resolution to mesoscopic scales. Here we detect the natural fluctuations of nanoscale spin ensembles at ambient temperatures by measuring the decoherence rate of a single quantum spin in response to introduced extrinsic target spins. In our experiments 45 nm nanodiamonds with single nitrogen-vacancy (NV) spins were immersed in solution containing spin 5/2 Mn^2+ ions and the NV decoherence rate measured though optically detected magnetic resonance. The presence of both freely moving and accreted Mn spins in solution were detected via significant changes in measured NV decoherence rates. Analysis of the data using a quantum cluster expansion treatment of the NV-target system found the measurements to be consistent with the detection of ~2,500 motionally diffusing Mn spins over an effective volume of (16 nm)^3 in 4.2 s, representing a reduction in target ensemble size and acquisition time of several orders of magnitude over state-of-the-art electron spin resonance detection. These measurements provide the basis for the detection of nanoscale magnetic field fluctuations with unprecedented sensitivity and resolution in ambient conditions.

cond-mat.mes-hall↗

arXiv2011

Relative intensity squeezing by four-wave mixing with loss: an analytic model and experimental diagnostic

Four-wave mixing near resonance in an atomic vapor can produce relative intensity squeezed light suitable for precision measurements beyond the shot-noise limit. We develop an analytic distributed gain/loss model to describe the competition of mixing and absorption through the non-linear medium. Using a novel matrix calculus, we present closed-form expressions for the degree of relative intensity squeezing produced by this system. We use these theoretical results to analyze experimentally measured squeezing from a $^{85}$Rb vapor and demonstrate the analytic model's utility as an experimental diagnostic.

quant-ph↗

arXiv2005

Diffraction-contrast imaging of cold atoms

We consider the inverse problem of in-line holography, applied to minimally-destructive imaging of cold atom clouds. Absorption imaging near-resonance provides a simple, but destructive measurement of atom column density. Imaging off resonance greatly reduces heating, and sequential images may be taken. Under the conditions required for off-resonant imaging, the generally-intractable inverse problem may be linearized. A minimally-destructive, quantitative and high-resolution image of the atom cloud column density is then retrieved from a single diffraction pattern.

physics.atom-ph↗