13 research outputs found
Notions of controllability for quantum mechanical systems
In this paper, we define four different notions of controllability of
physical interest for multilevel quantum mechanical systems. These notions
involve the possibility of driving the evolution operator as well as the state
of the system. We establish the connections among these different notions as
well as methods to verify controllability.
The paper also contains results on the relation between the controllability
in arbitrary small time of a system varying on a compact transformation Lie
group and the corresponding system on the associated homogeneous space. As an
application, we prove that, for the system of two interacting spin 1/2
particles, not every state transfer can be obtained in arbitrary small time.Comment: Replaced by a new version which contains the proof
Degrees of controllability for quantum systems and applications to atomic systems
Precise definitions for different degrees of controllability for quantum
systems are given, and necessary and sufficient conditions are discussed. The
results are applied to determine the degree of controllability for various
atomic systems with degenerate energy levels and transition frequencies.Comment: 20 pages, IoP LaTeX, revised and expanded versio
Constructive control of quantum systems using factorization of unitary operators
We demonstrate how structured decompositions of unitary operators can be
employed to derive control schemes for finite-level quantum systems that
require only sequences of simple control pulses such as square wave pulses with
finite rise and decay times or Gaussian wavepackets. To illustrate the
technique it is applied to find control schemes to achieve population transfers
for pure-state systems, complete inversions of the ensemble populations for
mixed-state systems, create arbitrary superposition states and optimize the
ensemble average of dynamic observables.Comment: 28 pages, IoP LaTeX, principal author has moved to Cambridge
University ([email protected]
Information-technology approach to quantum feedback control
Quantum control theory is profitably reexamined from the perspective of
quantum information, two results on the role of quantum information technology
in quantum feedback control are presented and two quantum feedback control
schemes, teleportation-based distant quantum feedback control and quantum
feedback control with quantum cloning, are proposed. In the first feedback
scheme, the output from the quantum system to be controlled is fed back into
the distant actuator via teleportation to alter the dynamics of system. The
result theoretically shows that it can accomplish some tasks such as distant
feedback quantum control that Markovian or Bayesian quantum feedback can't
complete. In the second feedback strategy, the design of quantum feedback
control algorithms is separated into a state recognition step, which gives
"on-off" signal to the actuator through recognizing some copies from the
cloning machine, and a feedback (control) step using another copies of cloning
machine. A compromise between information acquisition and measurement
disturbance is established, and this strategy can perform some quantum control
tasks with coherent feedback.Comment: 10 pages,submitte
Impact of positivity and complete positivity on accessibility of Markovian dynamics
We consider a two-dimensional quantum control system evolving under an
entropy-increasing irreversible dynamics in the semigroup form. Considering a
phenomenological approach to the dynamics, we show that the accessibility
property of the system depends on whether its evolution is assumed to be
positive or completely positive. In particular, we characterize the family of
maps having different accessibility and show the impact of that property on
observable quantities by means of a simple physical model.Comment: 11 pages, to appear in J. Phys.
On Quantum State Observability and Measurement
We consider the problem of determining the state of a quantum system given
one or more readings of the expectation value of an observable. The system is
assumed to be a finite dimensional quantum control system for which we can
influence the dynamics by generating all the unitary evolutions in a Lie group.
We investigate to what extent, by an appropriate sequence of evolutions and
measurements, we can obtain information on the initial state of the system. We
present a system theoretic viewpoint of this problem in that we study the {\it
observability} of the system. In this context, we characterize the equivalence
classes of indistinguishable states and propose algorithms for state
identification
Evaluation of air contamination in orthopaedic operating theatres in hospitals in Southern Italy: The IMPACT project
Postoperative infections are a concern, especially in total knee and total hip arthroplasty. We evaluated the air quality in orthopaedic operating theatres in southeastern Italy to determine the level of bacterial contamination as a risk factor for postoperative infection. Thirty-five hospitals with operating theatres focused on total knee and total hip arthroplasty participated. We sampled the air passively and actively before surgeries began for the day (at rest) and 15 min after the surgical incision (in operation). We evaluated bacterial counts, particle size, mixed vs turbulent airflow systems, the number of doors, number of door openings during procedures and number of people in the operating theatre. We found no bacterial contamination at rest for all sampling methods, and significantly different contamination levels at rest vs in operation. We found no association between the number of people in the surgical team and bacteria counts for both mixed and turbulent airflow systems, and low bacterial loads, even when doors were always open. Overall, the air quality sampling method and type of ventilation system did not affect air quality