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Articles 181 - 210 of 252
Full-Text Articles in Quantum Physics
New Insights On Emergence From The Perspective Of Weak Values And Dynamical Non-Locality, Jeff Tollaksen
New Insights On Emergence From The Perspective Of Weak Values And Dynamical Non-Locality, Jeff Tollaksen
Mathematics, Physics, and Computer Science Faculty Articles and Research
In this article, we will examine new fundamental aspects of "emergence" and "information" using novel approaches to quantum mechanics which originated from the group around Aharonov. The two-state vector formalism provides a complete description of pre- and post-selected quantum systems and has uncovered a host of new quantum phenomena which were previously hidden. The most important feature is that any weak coupling to a pre- and post-selected system is effectively a coupling to a "weak value" which is given by a simple expression depending on the two-state vector. In particular, weak values, are the outcomes of so called "weak measurements" …
Observation Of A Quantum Cheshire Cat In A Matter-Wave Interferometer Experiment, Tobias Denkmayr, Hermann Geppert, Stephan Sponar, Hartmut Lemmel, Alexandre Matzkin, Jeff Tollaksen, Yuji Hasegawa
Observation Of A Quantum Cheshire Cat In A Matter-Wave Interferometer Experiment, Tobias Denkmayr, Hermann Geppert, Stephan Sponar, Hartmut Lemmel, Alexandre Matzkin, Jeff Tollaksen, Yuji Hasegawa
Mathematics, Physics, and Computer Science Faculty Articles and Research
From its very beginning, quantum theory has been revealing extraordinary and counter-intuitive phenomena, such as wave-particle duality, Schrodinger cats and quantum non-locality. Another paradoxical phenomenon found within the framework of quantum mechanics is the 'quantum Cheshire Cat': if a quantum system is subject to a certain pre- and postselection, it can behave as if a particle and its property are spatially separated. It has been suggested to employ weak measurements in order to explore the Cheshire Cat's nature. Here we report an experiment in which we send neutrons through a perfect silicon crystal interferometer and perform weak measurements to probe …
Ψ-Epistemic Models Are Exponentially Bad At Explaining The Distinguishability Of Quantum States, Matthew S. Leifer
Ψ-Epistemic Models Are Exponentially Bad At Explaining The Distinguishability Of Quantum States, Matthew S. Leifer
Mathematics, Physics, and Computer Science Faculty Articles and Research
The status of the quantum state is perhaps the most controversial issue in the foundations of quantum theory. Is it an epistemic state (state of knowledge) or an ontic state (state of reality)? In realist models of quantum theory, the epistemic view asserts that nonorthogonal quantum states correspond to overlapping probability measures over the true ontic states. This naturally accounts for a large number of otherwise puzzling quantum phenomena. For example, the indistinguishability of nonorthogonal states is explained by the fact that the ontic state sometimes lies in the overlap region, in which case there is nothing in reality that …
Quantum Non-Barking Dogs, Sara Imari Walker, Paul C. W. Davies, Prasant Samantray, Yakir Aharonov
Quantum Non-Barking Dogs, Sara Imari Walker, Paul C. W. Davies, Prasant Samantray, Yakir Aharonov
Mathematics, Physics, and Computer Science Faculty Articles and Research
Quantum weak measurements with states both pre- and post-selected offer a window into a hitherto neglected sector of quantum mechanics. A class of such systems involves time dependent evolution with transitions possible. In this paper we explore two very simple systems in this class. The first is a toy model representing the decay of an excited atom. The second is the tunneling of a particle through a barrier. The post-selection criteria are chosen as follows: at the final time, the atom remains in its initial excited state for the first example and the particle remains behind the barrier for the …
Quantum Harmonic Oscillator With Superoscillating Initial Datum, Roman V. Buniy, Fabrizio Colombo, Irene Sabadini, Daniele C. Struppa
Quantum Harmonic Oscillator With Superoscillating Initial Datum, Roman V. Buniy, Fabrizio Colombo, Irene Sabadini, Daniele C. Struppa
Mathematics, Physics, and Computer Science Faculty Articles and Research
In this paper, we study the evolution of superoscillating initial data for the quantum driven harmonic oscillator. Our main result shows that superoscillations are amplified by the harmonic potential and that the analytic solution develops a singularity in finite time. We also show that for a large class of solutions of the Schrodinger equation, superoscillating behavior at any given time implies superoscillating behavior at any other time.
Foundations And Applications Of Weak Quantum Measurements, Yakir Aharonov, Eliahu Cohen, Avshalom C. Elitzur
Foundations And Applications Of Weak Quantum Measurements, Yakir Aharonov, Eliahu Cohen, Avshalom C. Elitzur
Mathematics, Physics, and Computer Science Faculty Articles and Research
Weak quantum measurement (WM) is unique in measuring noncommuting operators and other peculiar, otherwise-undetectable phenomena predicted by the two-state-vector-formalism (TSVF). The aim of this article is threefold: (i) introducing the foundations of WM and TSVF, (ii) studying temporal peculiarities predicted by TSVF and manifested by WM, and (iii) presenting applications of WM to single particles.
Is The Quantum State Real? An Extended Review Of Psi-Ontology Theorems, Matthew S. Leifer
Is The Quantum State Real? An Extended Review Of Psi-Ontology Theorems, Matthew S. Leifer
Mathematics, Physics, and Computer Science Faculty Articles and Research
Towards the end of 2011, Pusey, Barrett and Rudolph derived a theorem that aimed to show that the quantum state must be ontic (a state of reality) in a broad class of realist approaches to quantum theory. This result attracted a lot of attention and controversy. The aim of this review article is to review the background to the Pusey–Barrett–Rudolph Theorem, to provide a clear presentation of the theorem itself, and to review related work that has appeared since the publication of the Pusey–Barrett–Rudolph paper. In particular, this review: Explains what it means for the quantum state to be ontic …
A Bayesian Approach To Compatibility, Improvement, And Pooling Of Quantum States, Matthew S. Leifer, Robert W. Spekkens
A Bayesian Approach To Compatibility, Improvement, And Pooling Of Quantum States, Matthew S. Leifer, Robert W. Spekkens
Mathematics, Physics, and Computer Science Faculty Articles and Research
In approaches to quantum theory in which the quantum state is regarded as a representation of knowledge, information, or belief, two agents can assign different states to the same quantum system. This raises two questions: when are such state assignments compatible? and how should the state assignments of different agents be reconciled? In this paper, we address these questions from the perspective of the recently developed conditional states formalism for quantum theory [1]. Specifically, we derive a compatibility criterion proposed by Brun, Finkelstein and Mermin from the requirement that, upon acquiring data, agents should update their states using a quantum …
From Quanta To Qualia: How A Paradigm Shift Turns Into Science. Philosophy Study Vol. 4, Deepak Chopra, Menas Kafatos
From Quanta To Qualia: How A Paradigm Shift Turns Into Science. Philosophy Study Vol. 4, Deepak Chopra, Menas Kafatos
Mathematics, Physics, and Computer Science Faculty Articles and Research
Ever since the development of quantum mechanics in the first part of the 20th century, a new world view has emerged. Today, the physicalist objective assumption that objects exist independently of acts of observation has been challenged. The repercussions of this radical challenge to our common-sense perception of the world are far-reaching, although not yet generally realized. Here we argue that there is a complementary view to the way science which is being practiced, and that consciousness itself is primary and qualia form the foundation of experience. We outline the arguments of why the new science of qualia will tie …
Action Principle For Continuous Quantum Measurement, A. Chantasri, Justin Dressel, Andrew N. Jordan
Action Principle For Continuous Quantum Measurement, A. Chantasri, Justin Dressel, Andrew N. Jordan
Mathematics, Physics, and Computer Science Faculty Articles and Research
We present a stochastic path integral formalism for continuous quantum measurement that enables the analysis of rare events using action methods. By doubling the quantum state space to a canonical phase space, we can write the joint probability density function of measurement outcomes and quantum state trajectories as a phase space path integral. Extremizing this action produces the most likely paths with boundary conditions defined by preselected and postselected states as solutions to a set of ordinary differential equations. As an application, we analyze continuous qubit measurement in detail and examine the structure of a quantum jump in the Zeno …
Strengthening Weak-Value Amplification With Recycled Photons, Justin Dressel, Kevin Lyons, Andrew N. Jordan, Trent M. Graham, Paul G. Kwiat
Strengthening Weak-Value Amplification With Recycled Photons, Justin Dressel, Kevin Lyons, Andrew N. Jordan, Trent M. Graham, Paul G. Kwiat
Mathematics, Physics, and Computer Science Faculty Articles and Research
We consider the use of cyclic weak measurements to improve the sensitivity of weak-value amplification precision measurement schemes. Previous weak-value experiments have used only a small fraction of events, while discarding the rest through the process of “postselection.” We extend this idea by considering recycling of events which are typically unused in a weak measurement. Here we treat a sequence of polarized laser pulses effectively trapped inside an interferometer using a Pockels cell and polarization optics. In principle, all photons can be postselected, which will improve the measurement sensitivity. We first provide a qualitative argument for the expected improvements from …
Quantum Instruments As A Foundation For Both States And Observables, Justin Dressel, Andrew N. Jordan
Quantum Instruments As A Foundation For Both States And Observables, Justin Dressel, Andrew N. Jordan
Mathematics, Physics, and Computer Science Faculty Articles and Research
We demonstrate that quantum instruments can provide a unified operational foundation for quantum theory. Since these instruments directly correspond to laboratory devices, this foundation provides an alternate, more experimentally grounded, perspective from which to understand the elements of the traditional approach.We first show that in principle all measurable probabilities and correlations can be expressed entirely in terms of quantum instruments without the need for conventional quantum states or observables. We then show how these states and observables reappear as derived quantities by conditioning joint detection probabilities on the first or last measurement in a sequence as a preparation or a …
Null Values And Quantum State Discrimination, Oded Zilberberg, Alessandro Romito, David J. Starling, Gregory A. Howland, Curtis J. Broadbent, John C. Howell, Yuval Gefen
Null Values And Quantum State Discrimination, Oded Zilberberg, Alessandro Romito, David J. Starling, Gregory A. Howland, Curtis J. Broadbent, John C. Howell, Yuval Gefen
Mathematics, Physics, and Computer Science Faculty Articles and Research
We present a measurement protocol for discriminating between two different quantum states of a qubit with high fidelity. The protocol, called null value, is comprised of a projective measurement performed on the system with a small probability (also known as partial collapse), followed by a tuned postselection. We report on an optical experimental implementation of the scheme. We show that our protocol leads to an amplified signal-to-noise ratio (as compared with a straightforward strong measurement) when discerning between the two quantum states.
Maximally Epistemic Interpretations Of The Quantum State And Contextuality, Matthew S. Leifer, O. J. E. Maroney
Maximally Epistemic Interpretations Of The Quantum State And Contextuality, Matthew S. Leifer, O. J. E. Maroney
Mathematics, Physics, and Computer Science Faculty Articles and Research
We examine the relationship between quantum contextuality (in both the standard Kochen-Specker sense and in the generalized sense proposed by Spekkens) and models of quantum theory in which the quantum state is maximally epistemic.We find that preparation noncontextual models must be maximally epistemic, and these in turn must be Kochen-Specker noncontextual. This implies that the Kochen-Specker theorem is sufficient to establish both the impossibility of maximally epistemic models and the impossibility of preparation noncontextual models. The implication from preparation noncontextual to maximally epistemic then also yields a proof of Bell’s theorem from an Einstein-Podolsky-Rosen-like argument.
The Classical Limit Of Quantum Optics: Not What It Seems At First Sight, Yakir Aharonov, Alonso Botero, Shmuel Nussinov, Sandu Popescu, Jeff Tollaksen, Lev Vaidman
The Classical Limit Of Quantum Optics: Not What It Seems At First Sight, Yakir Aharonov, Alonso Botero, Shmuel Nussinov, Sandu Popescu, Jeff Tollaksen, Lev Vaidman
Mathematics, Physics, and Computer Science Faculty Articles and Research
What light is and how to describe it has always been a central subject in physics. As our understanding has increased, so have our theories changed: geometrical optics, wave optics and quantum optics are increasingly sophisticated descriptions, each referring to a larger class of phenomena than its predecessor. But how exactly are these theories related? How and when wave optics reduces to geometric optics is a rather simple problem. Similarly, how quantum optics reduces to wave optics has also been considered to be a very simple business. It is not so. As we show here the classical limit of quantum …
Quantum Cheshire Cats, Yakir Aharonov, Sandu Popescu, Daniel Rohrlich, Paul Skrzypczyk
Quantum Cheshire Cats, Yakir Aharonov, Sandu Popescu, Daniel Rohrlich, Paul Skrzypczyk
Mathematics, Physics, and Computer Science Faculty Articles and Research
In this paper we present a quantum Cheshire Cat. In a pre- and post-selected experiment we find the Cat in one place, and its grin in another. The Cat is a photon, while the grin is its circular polarization.
Towards A Formulation Of Quantum Theory As A Causally Neutral Theory Of Bayesian Inference, Matthew S. Leifer, Robert W. Spekkens
Towards A Formulation Of Quantum Theory As A Causally Neutral Theory Of Bayesian Inference, Matthew S. Leifer, Robert W. Spekkens
Mathematics, Physics, and Computer Science Faculty Articles and Research
Quantum theory can be viewed as a generalization of classical probability theory, but the analogy as it has been developed so far is not complete. Whereas themanner in which inferences aremade in classical probability theory is independent of the causal relation that holds between the conditioned variable and the conditioning variable, in the conventional quantum formalism, there is a significant difference between how one treats experiments involving two systems at a single time and those involving a single system at two times. In this article, we develop the formalism of quantum conditional states, which provides a unified description of …
Point–Counterpoint: Can Anything Be Learned From Surveys On The Interpretations Of Quantum Mechanics?, Matthew S. Leifer, Nathan Harshman
Point–Counterpoint: Can Anything Be Learned From Surveys On The Interpretations Of Quantum Mechanics?, Matthew S. Leifer, Nathan Harshman
Mathematics, Physics, and Computer Science Faculty Articles and Research
"In what follows, Matt Leifer and Nathan Harshman present opposing views on the value of surveys on foundational attitudes towards quantum mechanics. Three such surveys were recently published and their results are summarized in Table 1. Matt takes the `point,’ arguing that such surveys are not useful, while Nathan takes the `counterpoint.’ A complete set of references for both is given at the end."
Review Of Computing With Quantum Cats: From Colossus To Qubits And Schrödinger’S Killer App: Race To Build The World’S First Quantum Computer, Matthew S. Leifer
Review Of Computing With Quantum Cats: From Colossus To Qubits And Schrödinger’S Killer App: Race To Build The World’S First Quantum Computer, Matthew S. Leifer
Mathematics, Physics, and Computer Science Faculty Articles and Research
Book reviews of Computing With Quantum Cats: From Colossus To Qubits by John Gribbin and Schrödinger’s Killer App: Race To Build The World’s First Quantum Computer by John Dowling.
Weak Values Are Universal In Von Neumann Measurements, Justin Dressel, Andrew N. Jordan
Weak Values Are Universal In Von Neumann Measurements, Justin Dressel, Andrew N. Jordan
Mathematics, Physics, and Computer Science Faculty Articles and Research
We refute the widely held belief that the quantum weak value necessarily pertains to weak measurements. To accomplish this, we use the transverse position of a beam as the detector for the conditioned von Neumann measurement of a system observable. For any coupling strength, any initial states, and any choice of conditioning, the averages of the detector position and momentum are completely described by the real parts of three generalized weak values in the joint Hilbert space. Higher-order detector moments also have similar weak value expansions. Using the Wigner distribution of the initial detector state, we find compact expressions for …
Quantum Mutual Information Capacity For High-Dimensional Entangled States, P. Ben Dixon, Gregory A. Howland, James Schneeloch, John C. Howell
Quantum Mutual Information Capacity For High-Dimensional Entangled States, P. Ben Dixon, Gregory A. Howland, James Schneeloch, John C. Howell
Mathematics, Physics, and Computer Science Faculty Articles and Research
High-dimensional Hilbert spaces used for quantum communication channels offer the possibility of large data transmission capabilities. We propose a method of characterizing the channel capacity of an entangled photonic state in high-dimensional position and momentum bases. We use this method to measure the channel capacity of a parametric down-conversion state by measuring in up to 576 dimensions per detector. We achieve a channel capacity over 7 bits/photon in either the position or momentum basis. Furthermore, we provide a correspondingly high-dimensional separability bound that suggests that the channel performance cannot be replicated classically.
Contextual-Value Approach To The Generalized Measurement Of Observables, Justin Dressel, Andrew N. Jordan
Contextual-Value Approach To The Generalized Measurement Of Observables, Justin Dressel, Andrew N. Jordan
Mathematics, Physics, and Computer Science Faculty Articles and Research
We present a detailed motivation for and definition of the contextual values of an observable, which were introduced by Dressel et al. [Phys. Rev. Lett. 104, 240401 (2011)]. The theory of contextual values is a principled approach to the generalized measurement of observables. It extends the well-established theory of generalized statemeasurements by bridging the gap between partial state collapse and the observables that represent physically relevant information about the system. To emphasize the general utility of the concept, we first construct the full theory of contextual values within an operational formulation of classical probability theory, paying special attention to observable …
Measuring Which-Path Information With Coupled Electronic Mach-Zehnder Interferometers, Justin Dressel, Y. Choi, Andrew N. Jordan
Measuring Which-Path Information With Coupled Electronic Mach-Zehnder Interferometers, Justin Dressel, Y. Choi, Andrew N. Jordan
Mathematics, Physics, and Computer Science Faculty Articles and Research
We theoretically investigate a generalized “which-path” measurement on an electronic Mach-Zehnder Interferometer (MZI) implemented via Coulomb coupling to a second electronic MZI acting as a detector. The use of contextual values, or generalized eigenvalues, enables the precise construction of which-path operator averages that are valid for any measurement strength from the available drain currents. The form of the contextual values provides direct physical insight about the measurement being performed, providing information about the correlation strength between system and detector, the measurement inefficiency, and the proper background removal. We find that the detector interferometer must display maximal wavelike behavior to optimally …
Significance Of The Imaginary Part Of The Weak Value, Justin Dressel, Andrew N. Jordan
Significance Of The Imaginary Part Of The Weak Value, Justin Dressel, Andrew N. Jordan
Mathematics, Physics, and Computer Science Faculty Articles and Research
Unlike the real part of the generalized weak value of an observable, which can in a restricted sense be operationally interpreted as an idealized conditioned average of that observable in the limit of zero measurement disturbance, the imaginary part of the generalized weak value does not provide information pertaining to the observable being measured.What it does provide is direct information about howthe initial statewould be unitarily disturbed by the observable operator. Specifically, we provide an operational interpretation for the imaginary part of the generalized weak value as the logarithmic directional derivative of the postselection probability along the unitary flow generated …
Teleportation In General Probabilistic Theories, Howard Barnum, Jonathan Barrett, Matthew S. Leifer, Alex Wilce
Teleportation In General Probabilistic Theories, Howard Barnum, Jonathan Barrett, Matthew S. Leifer, Alex Wilce
Mathematics, Physics, and Computer Science Faculty Articles and Research
In a previous paper, we showed that many important quantum information-theoretic phenomena, including the no-cloning and no-broadcasting theorems, are in fact generic in all non-classical probabilistic theories. An exception is teleportation, which most such theories do not support. In this paper, we investigate which probabilistic theories, and more particularly, which composite systems, do support a teleportation protocol. We isolate a natural class of composite systems that we term regular, and establish necessary and sufficient conditions for a regular tripartite system to support a conclusive, or post-selected, teleportation protocol. We also establish a sufficient condition for deterministic teleportation that yields …
Response To Griffiths, Matthew S. Leifer
Response To Griffiths, Matthew S. Leifer
Mathematics, Physics, and Computer Science Faculty Articles and Research
"First of all, I would like to thank Prof. Griffith for his comments. The exchange has reminded me of the series of letters that appeared in Physics Today following the publication of an article by Chandralekha Singh, Mario Belloni, and Wolfgang Christian on improving the teaching of undergraduate quantum mechanics (see http://ptonline.aip.org/ journals/doc/PHTOAD-ft/vol_60/iss_3/8_1.shtml). In those responses, both Griffiths and Travis Norsen argued that students’ understanding of quantum mechanics would be vastly improved if they were taught more about the foundations of quantum theory, and I wholeheartedly agree with that sentiment. The thing is, Griffiths argued vociferously that this should be …
Review Of The Mathematical Language Of Quantum Theory: From Uncertainty To Entanglement, Matthew S. Leifer
Review Of The Mathematical Language Of Quantum Theory: From Uncertainty To Entanglement, Matthew S. Leifer
Mathematics, Physics, and Computer Science Faculty Articles and Research
A book review of The Mathematical Language of Quantum Theory: From Uncertainty to Entanglement by Teiko Heinosaari and Mario Ziman.
New Invariants For Entangled States, Roman V. Buniy, Thomas W. Kephart
New Invariants For Entangled States, Roman V. Buniy, Thomas W. Kephart
Mathematics, Physics, and Computer Science Faculty Articles and Research
We propose new algebraic invariants that distinguish and classify entangled states. Considering qubits as well as higher spin systems, we obtained complete entanglement classifications for cases that were either unsolved or only conjectured in the literature.
Entropy And Information Causality In General Probabilistic Theories (Addendum), Howard Barnum, Jonathan Barrett, Lisa Orloff Clark, Matthew S. Leifer, Robert Spekkens, Nicholas Stepanik, Alex Wilce, Robin Wilke
Entropy And Information Causality In General Probabilistic Theories (Addendum), Howard Barnum, Jonathan Barrett, Lisa Orloff Clark, Matthew S. Leifer, Robert Spekkens, Nicholas Stepanik, Alex Wilce, Robin Wilke
Mathematics, Physics, and Computer Science Faculty Articles and Research
In this addendum to our paper (2010 New J. Phys. 12 033024), we point out that an elementary consequence of the strong subadditivity inequality allows us to strengthen one of the main conclusions of that paper.
Pbr, Epr, And All That Jazz, Matthew S. Leifer
Pbr, Epr, And All That Jazz, Matthew S. Leifer
Mathematics, Physics, and Computer Science Faculty Articles and Research
"In the past couple of months, the quantum foundations world has been abuzz about a new preprint entitled "The Quantum State Cannot be Interpreted Statistically" by Matt Pusey, Jon Barrett and Terry Rudolph (henceforth known as PBR). Since I wrote a blog post explaining the result, I have been inundated with more correspondence from scientists and more requests for comment from science journalists than at any other point in my career. Reaction to the result amongst quantum researchers has been mixed, with many people reacting negatively to the title, which can be misinterpreted as an attack on the Born rule. …