10 research outputs found
Charge stability and charge-state-based spin readout of shallow nitrogen-vacancy centers in diamond
Spin-based applications of the negatively charged nitrogen-vacancy (NV)
center in diamonds require efficient spin readout. One approach is the
spin-to-charge conversion (SCC), relying on mapping the spin states onto the
neutral (NV) and negative (NV) charge states followed by a subsequent
charge readout. With high charge-state stability, SCC enables extended
measurement times, increasing precision and minimizing noise in the readout
compared to the commonly used fluorescence detection. Nano-scale sensing
applications, however, require shallow NV centers within a few \si{\nano
\meter} distance from the surface where surface related effects might degrade
the NV charge state. In this article, we investigate the charge state
initialization and stability of single NV centers implanted \approx
\SI{5}{\nano \meter} below the surface of a flat diamond plate. We demonstrate
the SCC protocol on four shallow NV centers suitable for nano-scale sensing,
obtaining a reduced readout noise of 5--6 times the spin-projection noise
limit. We investigate the general applicability of SCC for shallow NV centers
and observe a correlation between NV charge-state stability and readout noise.
Coating the diamond with glycerol improves both charge initialization and
stability. Our results reveal the influence of the surface-related charge
environment on the NV charge properties and motivate further investigations to
functionalize the diamond surface with glycerol or other materials for
charge-state stabilization and efficient spin-state readout of shallow NV
centers suitable for nano-scale sensing.Comment: 9 pages, 5 figure
Collective excitations of a two-dimensional interacting Bose gas in anti-trap and linear external potentials
We present a method of finding approximate analytical solutions for the
spectra and eigenvectors of collective modes in a two-dimensional system of
interacting bosons subjected to a linear external potential or the potential of
a special form , where is the chemical
potential. The eigenvalue problem is solved analytically for an artificial
model allowing the unbounded density of the particles. The spectra of
collective modes are calculated numerically for the stripe, the rare density
valley and the edge geometry and compared with the analytical results. It is
shown that the energies of the modes localized at the rare density region and
at the edge are well approximated by the analytical expressions. We discuss
Bose-Einstein condensation (BEC) in the systems under investigations at and find that in case of a finite number of the particles the regime of BEC
can be realized, whereas the condensate disappears in the thermodynamic limit.Comment: 10 pages, 2 figures include
Recommended from our members
Waveguide for cold atoms: Spin-1 magnetic particles and a filamentary current
We consider a waveguide for cold neutral atoms with a magnetic moment proportional to their spin angular momentum. The waveguide consists of a thin wire carrying a constant current. For the spin-1 case, we find bound states for the two-dimensional part of the motion around the wire, and present numerical and approximate analytic results for these bound states. In an experiment, the bound states can decay due to various effects, and we calculate the time scales involved.Physic
Active-passive calibration of optical tweezers in viscoelastic media
Mario Fischer, Andrew C. Richardson, S. Nader S. Reihani, Lene B. Oddershede, and Kirstine Berg-Sørense
Validation of FDT calibration method in complex media
Mario Fischera, Andrew C. Richardson, S. Nader S. Reihani, Lene Oddershede, and Kirstine Berg-Sørense
Quantitative determination of optical trapping strength and viscoelastic moduli inside living cells
With the success of in vitro single-molecule force measurements obtained in recent years, the next step is to perform quantitative force measurements inside a living cell. Optical traps have proven excellent tools for manipulation, also in vivo, where they can be essentially non-invasive under correct wavelength and exposure conditions. It is a pre-requisite for in vivo quantitative force measurements that a precise and reliable force calibration of the tweezers is performed. There are well-established calibration protocols in purely viscous environments; however, as the cellular cytoplasm is viscoelastic, it would be incorrect to use a calibration procedure relying on a viscous environment. Here we demonstrate a method to perform a correct force calibration inside a living cell. This method (theoretically proposed in Fischer and Berg-Sorensen (2007 J. Opt. A: Pure Appl. Opt. 9 S239)) takes into account the viscoelastic properties of the cytoplasm and relies on a combination of active and passive recordings of the motion of the cytoplasmic object of interest. The calibration procedure allows us to extract absolute values for the viscoelastic moduli of the living cell cytoplasm as well as the force constant describing the optical trap, thus paving the way for quantitative force measurements inside the living cell. Here, we determine both the spring constant of the optical trap and the elastic contribution from the cytoplasm, influencing the motion of naturally occurring tracer particles. The viscoelastic moduli that we find are of the same order of magnitude as moduli found in other cell types by alternative methods.</p
Optimal control of a nitrogen-vacancy spin ensemble in diamond for sensing in the pulsed domain
Defects in solid state materials provide an ideal, robust platform for
quantum sensing. To deliver maximum sensitivity, a large ensemble of
non-interacting defects hosting coherent quantum states are required. Control
of such an ensemble is challenging due to the spatial variation in both the
defect energy levels and in any control field across a macroscopic sample. In
this work we experimentally demonstrate that we can overcome these challenges
using Floquet theory and optimal control optimization methods to efficiently
and coherently control a large defect ensemble, suitable for sensing. We apply
our methods experimentally to a spin ensemble of up to 4 10
nitrogen vacancy (NV) centers in diamond. By considering the physics of the
system and explicitly including the hyperfine interaction in the optimization,
we design shaped microwave control pulses that can outperform conventional
(-) pulses when applied to sensing of temperature or magnetic field, with
a potential sensitivity improvement between 11 and 78\%. Through dynamical
modelling of the behaviour of the ensemble, we shed light on the physical
behaviour of the ensemble system and propose new routes for further
improvement