125 research outputs found
Gravitational sensing with weak value based optical sensors
Using weak values amplification angular resolution limits, we theoretically
investigate the gravitational sensing of objects. By inserting a force-sensing
pendulum into a weak values interferometer, the optical response can sense
accelerations to a few 10's of
, with optical powers of
. We convert this precision into range and mass sensitivity,
focusing in detail on simple and torsion pendula. Various noise sources present
are discussed, as well as the necessary cooling that should be applied to reach
the desired levels of precision.Comment: 9 pages, 4 figures, Quantum Stud.: Math. Found. (2018
Pontryagin-Optimal Control of a non-Hermitian Qubit
Open-system quantum dynamics described by non-Hermitian effective
Hamiltonians have become a subject of considerable interest. Studies of
non-Hermitian physics have revealed general principles, including relationships
between the topology of the complex eigenvalue space and the breakdown of
adiabatic control strategies. We study here the control of a single
non-Hermitian qubit, similar to recently realized experimental systems in which
the non-Hermiticity arises from an open spontaneous emission channel. We review
the topological features of the resulting non-Hermitian Hamiltonian and then
present two distinct results. First, we illustrate how to realize any
continuous and differentiable pure-state trajectory in the dynamics of a qubit
that are conditioned on no emission. This result implicitly provides a
workaround for the breakdown of standard adiabatic following in such
non-Hermitian systems. Second, we use Pontryagin's maximum principle to derive
optimal trajectories connecting boundary states on the Bloch sphere, using a
cost function which balances the desired dynamics against the controller energy
used to realize them. We demonstrate that the latter approach can effectively
find trajectories which maintain high state purity even in the case of
inefficient detection.Comment: 8 + 8 Pages, 7 Figure
Extracorporeal photochemotherapy for graft versus host disease : Where we are now and where are we going !
Graft-versus-host disease (GVHD) remains the leading cause of morbidity, non-relapse mortality and treatment failure post allogeneic hematopoietic stem cell transplantation (allo-HSCT). So far, steroids are the 1st line treatment but around 40% of patients become steroid-resistant or fail to respond at a safe dose. Patients who fail to respond to the initial therapy have a dismal prognosis and no standard treatment is well established for them to date. Treatments that modulate the immune system rather than directly suppressing its function, although not dampening a potential graft-versus-malignancy effect, would therefore be highly desirable and extracorporeal photopheresis (ECP) appeared as being a good candidate to fill in these criteria. Multiple reports of treatments in both paediatric and adult patients with GVHD have been published, and the overall favourable profile compared with other available immunosuppressive therapies continues to make ECP appealing despite all of the unknowns. In this article, we review the use of extracorporeal photopheresis for the treatment of graft-versus-host disease including technical aspects, mechanism of action, safety profile and clinical efficacy dat
Diffusive entanglement generation by continuous homodyne monitoring of spontaneous emission
We consider protocols to generate quantum entanglement between two remote
qubits, through joint time-continuous detection of their spontaneous emission.
We demonstrate that schemes based on homodyne detection, leading to diffusive
quantum trajectories, lead to identical average entanglement yield as
comparable photodetection strategies; this is despite substantial differences
in the two-qubit state dynamics between these schemes, which we explore in
detail. The ability to use different measurements to achieve the same ends may
be of practical significance; the less-well-known diffusive scheme appears far
more feasible on superconducting qubit platforms in the near term.Comment: 6 pages, 3 figures. Supplementary information can be found in the
longer version at arXiv:1910.0120
A Multi-Qubit Quantum Gate Using the Zeno Effect
The Zeno effect, in which repeated observation freezes the dynamics of a
quantum system, stands as an iconic oddity of quantum mechanics. When a
measurement is unable to distinguish between states in a subspace, the dynamics
within that subspace can be profoundly altered, leading to non-trivial
behavior. Here we show that such a measurement can turn a non-interacting
system with only single-qubit control into a two- or multi-qubit entangling
gate, which we call a Zeno gate. The gate works by imparting a geometric phase
on the system, conditioned on it lying within a particular nonlocal subspace.
We derive simple closed-form expressions for the gate fidelity under a number
of non-idealities and show that the gate is viable for implementation in
circuit and cavity QED systems. More specifically, we illustrate the
functioning of the gate via dispersive readout in both the Markovian and
non-Markovian readout regimes, and derive conditions for longitudinal readout
to ideally realize the gate.Comment: 20+12 pages. 13 figure
A Multi-Qubit Quantum Gate Using the Zeno Effect
The Zeno effect, in which repeated observation freezes the dynamics of a quantum system, stands as an iconic oddity of quantum mechanics. When a measurement is unable to distinguish between states in a subspace, the dynamics within that subspace can be profoundly altered, leading to non-trivial behavior. Here we show that such a measurement can turn a non-interacting system with only single-qubit control into a two- or multi-qubit entangling gate, which we call a Zeno gate. The gate works by imparting a geometric phase on the system, conditioned on it lying within a particular nonlocal subspace. We derive simple closed-form expressions for the gate fidelity under a number of non-idealities and show that the gate is viable for implementation in circuit and cavity QED systems. More specifically, we illustrate the functioning of the gate via dispersive readout in both the Markovian and non-Markovian readout regimes, and derive conditions for longitudinal readout to ideally realize the gate
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