arXiv subjects

P. W. Bryant

Publications and source records attributed to P. W. Bryant.

6 recordsLinked to original sources

arXiv2022

Exponential Decay and Fermi's Golden Rule from an Uncontrolled Quantum Zeno Effect

We modify the theory of the Quantum Zeno Effect to make it consistent with the postulates of quantum mechanics. This modification allows one, throughout a sequence of observations of an excited system, to address the nature of the observable and thereby to distinguish survival from non-decay, which is necessary whenever excited states are degenerate. As a consequence, one can determine which types of measurements can possibly inhibit the exponential decay of the system. We find that continuous monitoring taken as the limit of a sequence of ideal measurements will only inhibit decay in special cases, such as in well-controlled experiments. Uncontrolled monitoring of an unstable system, however, can cause exponentially decreasing non-decay probability at all times. Furthermore, calculating the decay rate for a general sequence of observations leads to a straightforward derivation of Fermi's Golden Rule, that avoids many of the conceptual difficulties normally encountered. When multiple decay channels are available, the derivation reveals how the total decay rate naturally partitions into a sum of the decay rates for the various channels, in agreement with observations. Continuous and unavoidable monitoring of an excited system by an uncontrolled environment may therefore be a mechanism by which to explain the exponential decay law.

quant-ph↗

arXiv2016

A platform for analysis of nanoscale liquids with an integrated sensor array based on 2-d material

Analysis of nanoscale liquids, including wetting and flow phenomena, is a scientific challenge with far reaching implications for industrial technologies. We report the conception, development, and application of an integrated platform for the experimental characterization of liquids at the nanometer scale. The platform combines the sensing functionalities of an integrated, two-dimensional electronic device array with in situ application of highly sensitive optical micro-spectroscopy and atomic force microscopy. We demonstrate the performance capabilities of the platform with an embodiment based on an array of integrated, optically transparent graphene sensors. The application of electronic and optical sensing in the platform allows for differentiating between liquids electronically, for determining a liquid's molecular fingerprint, and for monitoring surface wetting dynamics in real time. In order to explore the platform's sensitivity limits, we record topographies and optical spectra of individual, spatially isolated sessile oil emulsion droplets having volumes of less than ten attoliters. The results demonstrate that integrated measurement functionalities based on two-dimensional materials have the potential to push lab-on-chip based analysis from the microscale to the nanoscale.

physics.ins-det↗

arXiv2014

Quantitative $μ$PIV Measurements of Velocity Profiles

In Microscopic Particle Image Velocimetry ($μ$PIV), velocity fields in microchannels are sampled over finite volumes within which the velocity fields themselves may vary significantly. In the past, this has limited measurements often to be only qualitative in nature, blind to velocity magnitudes. In the pursuit of quantitatively useful results, one has treated the effects of the finite volume as errors that must be corrected by means of ever more complicated processing techniques. Resulting measurements have limited robustness and require convoluted efforts to understand measurement uncertainties. To increase the simplicity and utility of $μ$PIV measurements, we introduce a straightforward method, based directly on measurement, by which one can determine the size and shape of the volume over which moving fluids are sampled. By comparing measurements with simulation, we verify that this method enables quantitative measurement of velocity profiles across entire channels, as well as an understanding of experimental uncertainties. We show how the method permits measurement of an unknown flow rate through a channel of known geometry. We demonstrate the method to be robust against common sources of experimental uncertainty. We also apply the theory to model the technique of Scanning $μ$PIV, which is often used to locate the center of a channel, and we show how and why it can in fact misidentify the center. The results have general implications for research and development that requires reliable, quantitative measurement of fluid flow on the micrometer scale and below.

cond-mat.mes-hall↗

arXiv2011

Kinematic Effect of Indistinguishability and Its Application to Open Quantum Systems

In quantum mechanics, useful experiments require multiple measurements performed on the identically prepared physical objects composing experimental ensembles. Experimental systems also suffer from environmental interference, and one should not assume that all objects in the experimental ensemble suffer interference identically from a single, uncontrolled environment. Here we present a framework for treating multiple quantum environments and fluctuations affecting only subsets of the experimental ensemble. We also discuss a kinematic effect of indistinguishability not applicable to closed systems. As an application, we treat inefficient photon scattering as an open system. We also create a toy model for the environmental interference suffered by systems undergoing Rabi oscillations, and we find that this kinematic effect may explain the puzzling Excitation Induced Dephasing generally measured in experiments.

quant-ph↗

arXiv2010

Quantum decoherence without reduced dynamics

With a choice of boundary conditions for solutions of the Schrödinger equation, state vectors and density operators even for closed systems evolve asymmetrically in time. For open systems, standard quantum mechanics consequently predicts irreversibility and signatures of the extrinsic arrow of time. The result is a new framework for the treatment of decoherence, not based on a reduced dynamics or a master equation. As an application, using a general model we quantitatively match previously puzzling experimental results and can conclude that they are the measurable consequence of the indistinguishability of separate, uncontrolled interactions between systems and their environment.

quant-ph↗

arXiv2009

Quantum Dynamics With Intrinsic Time Asymmetry and Indistinguishable Events

The extrinsic quantum mechanical arrow of time is understood to be a consequence of the interaction between quantum systems and their environment. A choice of boundary conditions for the Schrödinger equation results in a different time asymmetry intrinsic to quantum mechanical dynamics and independent of environmental interactions. Correct application of the intrinsically asymmetric dynamics, however, leads unavoidably to predictions of the experimental signatures of the extrinsic arrow of time. We are led to a new, model-independent mechanism for quantum decoherence. We need not invoke a master equation or a phase-destroying, non-Hermitian Hamiltonian operator. As an application, we calculate predictive probabilities for the decoherence measured in Rabi oscillations experiments. We can also show that a previously puzzling experimental result, unexplained within the formalism of the quantum master equation, is in fact expected and is the measurable consequence of the indistinguishability of separate, uncontrolled interactions between systems and their environment.

quant-ph↗