36 research outputs found
Continuous dynamical decoupling magnetometry
Solid-state qubits hold the promise to achieve unmatched combination of
sensitivity and spatial resolution. To achieve their potential, the qubits need
however to be shielded from the deleterious effects of the environment. While
dynamical decoupling techniques can improve the coherence time, they impose a
compromise between sensitivity and bandwidth, since to higher decoupling power
correspond higher frequencies of the field to be measured. Moreover, the
performance of pulse sequences is ultimately limited by control bounds and
errors. Here we analyze a versatile alternative based on continuous driving. We
find that continuous dynamical decoupling schemes can be used for AC
magnetometry, providing similar frequency constraints on the AC field and
improved sensitivity for some noise regimes. In addition, the exibility of
phase and amplitude modulation could yield superior robustness to driving
errors and a better adaptability to external experimental scenarios
The NV center as a quantum actuator: time-optimal control of nuclear spins
Indirect control of qubits by a quantum actuator has been proposed as an
appealing strategy to manipulate qubits that couple only weakly to external
fields. While universal quantum control can be easily achieved when the
actuator-qubit coupling is anisotropic, the efficiency of this approach is less
clear. Here we analyze the time-efficiency of the quantum actuator control. We
describe a strategy to find time-optimal control sequence by the quantum
actuator and compare their gate times with direct driving, identifying regimes
where the actuator control performs faster. As an example, we focus on a
specific implementation based on the Nitrogen-Vacancy center electronic spin in
diamond (the actuator) and nearby carbon-13 nuclear spins (the qubits)
Algebraic synthesis of time-optimal unitaries in SU(2) with alternating controls
We present an algebraic framework to study the time-optimal synthesis of
arbitrary unitaries in SU(2), when the control set is restricted to rotations
around two non-parallel axes in the Bloch sphere. Our method bypasses commonly
used control-theoretical techniques, and easily imposes necessary conditions on
time-optimal sequences. In a straightforward fashion, we prove that
time-optimal sequences are solely parametrized by three rotation angles and
derive general bounds on those angles as a function of the relative rotation
speed of each control and the angle between the axes. Results are substantially
different whether both clockwise and counterclockwise rotations about the given
axes are allowed, or only clockwise rotations. In the first case, we prove that
any finite time-optimal sequence is composed at most of five control
concatenations, while for the more restrictive case, we present scaling laws on
the maximum length of any finite time-optimal sequence. The bounds we find for
both cases are stricter than previously published ones and severely constrain
the structure of time-optimal sequences, allowing for an efficient numerical
search of the time-optimal solution. Our results can be used to find the
time-optimal evolution of qubit systems under the action of the considered
control set, and thus potentially increase the number of realizable unitaries
before decoherence
Cathodoluminescence-based nanoscopic thermometry in a lanthanide-doped phosphor
Crucial to analyze phenomena as varied as plasmonic hot spots and the spread
of cancer in living tissue, nanoscale thermometry is challenging: probes are
usually larger than the sample under study, and contact techniques may alter
the sample temperature itself. Many photostable nanomaterials whose
luminescence is temperature-dependent, such as lanthanide-doped phosphors, have
been shown to be good non-contact thermometric sensors when optically excited.
Using such nanomaterials, in this work we accomplished the key milestone of
enabling far-field thermometry with a spatial resolution that is not
diffraction-limited at readout.
We explore thermal effects on the cathodoluminescence of lanthanide-doped
NaYF nanoparticles. Whereas cathodoluminescence from such lanthanide-doped
nanomaterials has been previously observed, here we use quantitative features
of such emission for the first time towards an application beyond localization.
We demonstrate a thermometry scheme that is based on cathodoluminescence
lifetime changes as a function of temperature that achieves 30 mK
sensitivity in sub-m nanoparticle patches. The scheme is robust against
spurious effects related to electron beam radiation damage and optical
alignment fluctuations.
We foresee the potential of single nanoparticles, of sheets of nanoparticles,
and also of thin films of lanthanide-doped NaYF to yield temperature
information via cathodoluminescence changes when in the vicinity of a sample of
interest; the phosphor may even protect the sample from direct contact to
damaging electron beam radiation. Cathodoluminescence-based thermometry is thus
a valuable novel tool towards temperature monitoring at the nanoscale, with
broad applications including heat dissipation in miniaturized electronics and
biological diagnostics.Comment: Main text: 30 pages + 4 figures; supplementary information: 22 pages
+ 8 figure
Achieving a quantum smart workforce
Interest in building dedicated Quantum Information Science and Engineering
(QISE) education programs has greatly expanded in recent years. These programs
are inherently convergent, complex, often resource intensive and likely require
collaboration with a broad variety of stakeholders. In order to address this
combination of challenges, we have captured ideas from many members in the
community. This manuscript not only addresses policy makers and funding
agencies (both public and private and from the regional to the international
level) but also contains needs identified by industry leaders and discusses the
difficulties inherent in creating an inclusive QISE curriculum. We report on
the status of eighteen post-secondary education programs in QISE and provide
guidance for building new programs. Lastly, we encourage the development of a
comprehensive strategic plan for quantum education and workforce development as
a means to make the most of the ongoing substantial investments being made in
QISE.Comment: 18 pages, 2 figures, 1 tabl
A Chirality-Based Quantum Leap
There is increasing interest in the study of chiral degrees of freedom occurring in matter and in electromagnetic fields. Opportunities in quantum sciences will likely exploit two main areas that are the focus of this Review: (1) recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials and (2) rapidly evolving nanophotonic strategies designed to amplify chiral light-matter interactions. On the one hand, the CISS effect underpins the observation that charge transport through nanoscopic chiral structures favors a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision and molecular modularity. On the other hand, chiral-optical effects that depend on both spin- and orbital-angular momentum of photons could offer key advantages in all-optical and quantum information technologies. In particular, amplification of these chiral light-matter interactions using rationally designed plasmonic and dielectric nanomaterials provide approaches to manipulate light intensity, polarization, and phase in confined nanoscale geometries. Any technology that relies on optimal charge transport, or optical control and readout, including quantum devices for logic, sensing, and storage, may benefit from chiral quantum properties. These properties can be theoretically and experimentally investigated from a quantum information perspective, which has not yet been fully developed. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to control the storage, transduction, and manipulation of quantum information. This forward-looking Review provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects and presents a vision for their possible future roles in enabling room-temperature quantum technologies.ISSN:1936-0851ISSN:1936-086