709 research outputs found
The Absolute Excitation Functions for the I 127 (n,y) I 128 and Na 23 (n,y) and Na 24 Reactions
Radiative capture (n,y) cross sections, in addition to their theoretical interest, are of great practical importance to the technology of reactor design. A knowledge of the absolute excitation functions of the various materials employed in reactors permits calculation of the effect of these materials on the reactivity of a reactor, and also enables shielding calculations to be made
Hamiltonian simulation algorithms for near-term quantum hardware
The quantum circuit model is the de-facto way of designing quantum algorithms. Yet any level of abstraction away from the underlying hardware incurs overhead. In this work, we develop quantum algorithms for Hamiltonian simulation "one level below” the circuit model, exploiting the underlying control over qubit interactions available in most quantum hardware and deriving analytic circuit identities for synthesising multi-qubit evolutions from two-qubit interactions. We then analyse the impact of these techniques under the standard error model where errors occur per gate, and an error model with a constant error rate per unit time. To quantify the benefits of this approach, we apply it to time-dynamics simulation of the 2D spin Fermi-Hubbard model. Combined with new error bounds for Trotter product formulas tailored to the non-asymptotic regime and an analysis of error propagation, we find that e.g. for a 5 × 5 Fermi-Hubbard lattice we reduce the circuit depth from 1, 243, 586 using the best previous fermion encoding and error bounds in the literature, to 3, 209 in the per-gate error model, or the circuit-depth-equivalent to 259 in the per-time error model. This brings Hamiltonian simulation, previously beyond reach of current hardware for non-trivial examples, significantly closer to being feasible in the NISQ era
Area law for fixed points of rapidly mixing dissipative quantum systems
We prove an area law with a logarithmic correction for the mutual information
for fixed points of local dissipative quantum system satisfying a rapid mixing
condition, under either of the following assumptions: the fixed point is pure,
or the system is frustration free.Comment: 17 pages, 1 figure. Final versio
Magnetic field control of cycloidal domains and electric polarization in multiferroic BiFeO
The magnetic field induced rearrangement of the cycloidal spin structure in
ferroelectric mono-domain single crystals of the room-temperature multiferroic
BiFeO is studied using small-angle neutron scattering (SANS). The cycloid
propagation vectors are observed to rotate when magnetic fields applied
perpendicular to the rhombohedral (polar) axis exceed a pinning threshold value
of 5\,T. In light of these experimental results, a phenomenological model
is proposed that captures the rearrangement of the cycloidal domains, and we
revisit the microscopic origin of the magnetoelectric effect. A new coupling
between the magnetic anisotropy and the polarization is proposed that explains
the recently discovered magnetoelectric polarization to the rhombohedral axis
Assessing non-Markovian dynamics
We investigate what a snapshot of a quantum evolution - a quantum channel
reflecting open system dynamics - reveals about the underlying continuous time
evolution. Remarkably, from such a snapshot, and without imposing additional
assumptions, it can be decided whether or not a channel is consistent with a
time (in)dependent Markovian evolution, for which we provide computable
necessary and sufficient criteria. Based on these, a computable measure of
`Markovianity' is introduced. We discuss how the consistency with Markovian
dynamics can be checked in quantum process tomography. The results also clarify
the geometry of the set of quantum channels with respect to being solutions of
time (in)dependent master equations.Comment: 5 pages, RevTex, 2 figures. (Except from typesetting) version to be
published in the Physical Review Letter
Extracting dynamical equations from experimental data is NP-hard
The behavior of any physical system is governed by its underlying dynamical
equations. Much of physics is concerned with discovering these dynamical
equations and understanding their consequences. In this work, we show that,
remarkably, identifying the underlying dynamical equation from any amount of
experimental data, however precise, is a provably computationally hard problem
(it is NP-hard), both for classical and quantum mechanical systems. As a
by-product of this work, we give complexity-theoretic answers to both the
quantum and classical embedding problems, two long-standing open problems in
mathematics (the classical problem, in particular, dating back over 70 years).Comment: For mathematical details, see arXiv:0908.2128[math-ph]. v2: final
version, accepted in Phys. Rev. Let
Square vortex lattice at anomalously low magnetic fields in electron-doped NdCeCuO
We report here on the first direct observations of the vortex lattice in the
bulk of electron-doped NdCeCuO single crystals. Using
small angle neutron scattering, we have observed a square vortex lattice with
the nearest-neighbors oriented at 45 from the Cu-O bond direction,
which is consistent with theories based on the d-wave superconducting gap.
However, the square symmetry persists down to unusually low magnetic fields.
Moreover, the diffracted intensity from the vortex lattice is found to decrease
rapidly with increasing magnetic field.Comment: 4 pages, 4 Figures, accepted for publication in Phys. Rev. Let
The Perioperative Nursing Workforce Program in NSW: How a professional perioperative nursing association meets one of its mandates Part 1
The need to review and change the way nursing care is delivered in perioperative settings is predicated on nursing workforce shortages, the changing, increasingly technologised and risk-prone OR practice milieu, and increasing demand for surgery. In responding to members' concerns about these issues, the NSW Operating Theatre Association Inc. (NSW OTA) in conjunction with and with sponsorship from the NSW Chief Nursing and Midwifery Officer, initiated and oversaw the development of a program, called the Perioperative Nursing Workforce Program (PNWP). The aims of this program are to make better use of human resources, to improve the way care is provided and thus improve patient outcomes; and to empower perioperative nurses so they are capable of independently improving their working environment. The program, which takes a practice development approach, program participants and some of their projects are presented in this paper. What is known about the topic The role of perioperative professional nursing associations is to write standards for practice and to assist in the professional development of their members. Practice development is hypothesised to assist clinical nurses to 'see' their work contexts afresh and to implement changes to improve patient care by focusing on patient-centredness and the use of credible evidence. What this article contributes It describes the contents and the implementation of a perioperative nursing workforce program, initiated by the NSW OTA and auspiced by the Chief Nursing and Midwifery Officer, NSW Health. The PNWP uses the tenets of practice development (PD) to achieve its aims and this is possibly the first use of PD in perioperative settings, and on a statewide basis
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