Proceedings

EPJ D Highlight - Quantum momentum

Schemes for measuring time-of-flight in classical mechanics (top) and quantum mechanics (bottom). In quantum mechanics, the classical particle is represented by a wave packet. Values of X indicate position and t time.

A new quantum-mechanical model has been developed that allows the momentum of quantum particles to be measured using a variant of the classical time-of-flight.

Quantum mechanics is an extraordinarily successful way of understanding the physical world at extremely small scales. Through it, a handful of rules can be used to explain the majority of experimentally observable phenomena. Occasionally, however, we come across a problem in classical mechanics that poses particular difficulties for translation into the quantum world. A new study published in EPJ D has provided some insights into one of them: momentum. The authors, theoretical physicists Fabio Di Pumpo and Matthias Freyberger from Ulm University, Germany, present an elegant mathematical model of quantum momentum that is accessible through another classical concept: time-of-flight.

Many people will recall the traditional definition of momentum from high-school physics as being the product of the mass of an object and the velocity at which it is travelling. In quantum theory an object is represented by a wave function and its position cannot be determined unless the wave function is 'collapsed' into a single state. This is the essence of measurement in quantum mechanics.

Classical momentum can be obtained simply by measuring the time an object takes to pass between two stationary detectors ('time-of-flight'), finding the velocity and multiplying by the mass. Di Pumpo and Freyberger have developed a model of the quantum equivalent of this experiment in which the roles of time and distance are reversed: the time points are fixed, and the probabilistic positions of a wave function at each point, and thus the distance between them, estimated. This approach uses additional quantum systems called pointers that are coupled to a moving wave packet using a method developed by von Neumann, with measurements made to the pointers rather than the wave.

Di Pumpo and Freyberger were thus able to derive a single, measurable quantity that is a quantum equivalent of the classical time-of-flight, and to calculate the momentum of a quantum particle quite precisely on this basis. They end the paper by suggesting ways of further improving the accuracy of the measurement.

F. Di Pumpo and M. Freyberger (2019) Pointer-based model for state reduction in momentum space, European Physical Journal D 73: 163, DOI: 10.1140/epjd/e2019-100226-1

This was our first experience of publishing with EPJ Web of Conferences. We contacted the publisher in the middle of September, just one month prior to the Conference, but everything went through smoothly. We have had published MNPS Proceedings with different publishers in the past, and would like to tell that the EPJ Web of Conferences team was probably the best, very quick, helpful and interactive. Typically, we were getting responses from EPJ Web of Conferences team within less than an hour and have had help at every production stage.
We are very thankful to Solange Guenot, Web of Conferences Publishing Editor, and Isabelle Houlbert, Web of Conferences Production Editor, for their support. These ladies are top-level professionals, who made a great contribution to the success of this issue. We are fully satisfied with the publication of the Conference Proceedings and are looking forward to further cooperation. The publication was very fast, easy and of high quality. My colleagues and I strongly recommend EPJ Web of Conferences to anyone, who is interested in quick high-quality publication of conference proceedings.

On behalf of the Organizing and Program Committees and Editorial Team of MNPS-2019, Dr. Alexey B. Nadykto, Moscow State Technological University “STANKIN”, Moscow, Russia. EPJ Web of Conferences vol. 224 (2019)

ISSN: 2100-014X (Electronic Edition)

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