A scheme for performing strong and weak sequential measurements of non-commuting observables

Quantum systems usually travel a multitude of different paths when evolving through time from an initial to a final state. In general, the possible paths will depend on the future and past boundary conditions, as well as the system's dynamics. We present a gedanken experiment where a single system apparently follows mutually exclusive paths simultaneously, each with probability one, depending on which measurement was performed. This experiment involves the measurement of observables that do not correspond to Hermitian operators. Our main result is a scheme for measuring these operators. The scheme is based on the erasure protocol [Phys. Rev. Lett. 116, 070404 (2016), arXiv:1409.1575] and allows a wide range of sequential measurements at both the weak and strong limits. At the weak limit the back action of the measurement cannot be used to account for the surprising behavior and the resulting weak values provide a consistent yet strange account of the system's past.Comment: Similar to published version, Quantum Studies: Mathematics and Foundations (2016). arXiv admin note: text overlap with arXiv:1409.157

Nonlocal measurements via quantum erasure

Non-local observables play an important role in quantum theory, from Bell inequalities and various post-selection paradoxes to quantum error correction codes. Instantaneous measurement of these observables is known to be a difficult problem, especially when the measurements are projective. The standard von Neumann Hamiltonian used to model projective measurements cannot be implemented directly in a non-local scenario and can, in some cases, violate causality. We present a scheme for effectively generating the von Neumann Hamiltonian for non-local observables without the need to communicate and adapt. The protocol can be used to perform weak and strong (projective) measurements, as well as measurements at any intermediate strength. It can also be used in practical situations beyond non-local measurements. We show how the protocol can be used to probe a version of Hardy's paradox with both weak and strong measurements. The outcomes of these measurements provide a non-intuitive picture of the pre- and post-selected system. Our results shed new light on the interplay between quantum measurements, uncertainty, non-locality, causality and determinism.Comment: Similar to published versio

Essays on the structural estimation and analysis of corporate and industrial markets

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Economics, 2009.Cataloged from PDF version of thesis.Includes bibliographical references.The three chapters which comprise my thesis are a collection of essays on the analysis of the corporate governance and airline markets and of the federal appellate structure. In Chapter 1, I use a discrete choice framework to analyze state design and firm choice of the implications of incorporation: corporate governance laws, corporate taxes and court structure. Firms - differentiated on ownership, management, industry concentration, financial profile and unobservable dimensions - freely choose their preferred state of incorporation or reincorporation. The revealed preference embedded in this observable choice is used as window into the heterogeneous preferences within and across firms, yielding several findings: For example, I find, surprisingly, that firms are very responsive to incorporation and franchise taxes. In addition, on average, firms like anti takeover statutes, but, consistent with an agency story, firms with an institutional shareholder block and venture capital backed firms dislike them. On average, firms dislike mandatory governance statutes restricting managerial power and facilitating the representation of minority shareholders, but these laws are less restrictive for the choice of firms in concentrated industries. All firms dislike well functioning courts, consistent with a litigation deterrence motive. The recovered firm preferences are then taken to the simulation of recently proposed federal reforms aimed at centralizing the domicile implications and restricting firm choice.(cont.) They are also related to the documented differential returns earned by firms with better internal governance in the 1990s, as well as to other (new) trading strategies that would have yielded abnormal returns in the 2000s. Chapter 2 begins with the observation that airlines choose the domestic markets - city pairs - they serve and the prices they charge given the structure of their network and the networks of rival airlines. I cast this choice into a dynamic oligopoly entry game to recover airline fixed and variable operating costs, entry costs, and profits, using a panel of 20 quarters of DB1B and T-100 Domestic Segment Data. These estimates are then used to analyze the strategic and cost saving effects of hubs, and LCC. I find that hubs are valuable to consumers and increase the variable profits of the hubbing airline, but when including fixed costs their desirability is much less clear. LCC, and especially Southwest and JetBlue are especially attractive to consumers, have lower marginal costs and have a strong negative impact on the profits of the incumbents in the markets they serve. In Chapter 3, using data on all federal civil trial and appellate cases from 1992-2003, I show that appeals are generally rejected and, for some case categories, can have negative expected net present value. Appellate outcomes can be further related to the trial decision being by judge or jury, the identity of the prevailing party (plaintiff or defendant, US or private), and the form of representation. Some of these factors influence the propensity to appeal, however, others, including whether trial was by judge or jury, go in the opposite way.(cont.) I discuss the implications of these findings for the modeling of the incentives to appeal and settlement breakdown, and for appellate reform.by Moshe Aharon Cohen.Ph.D

The Narrow Theta(1543)--A QCD Dilemma: Tube or Not Tube?

We argue that a width of less than MeV of the new Theta resonance is inconsistent with the observed ratio of resonance and background events in the various photon initiated experiments if the latter can be described by K, K*, etc., exchange. An evaluation of the Feynman diagrams which were believed to be relevant is presented and supports the general claim in the one case where a cross section has been given by the experimental group. More detailed arguments based on the flux tube model explaining the narrow widths and the apparent conflict with the production rates are presented. We predict narrow Tetra-quarks at mass ~ O(1-1.2 GeV) which the analysis of LEAR may have missed.Comment: 9 pages, 2 figures Please note that Nussinov has previously submitted entries to the ArXives through assistance of other individuals. The submitter of this paper ([email protected]) is L. Robinette, administrative assistant to the Maryland TQHN Group; comments should be addressed to [email protected]

Cell refinement of CsPbBr3 perovskite nanoparticles and thin films

In this work, we performed a detailed study of the phase transformations and structural unit cell parameters of CsPbBr3 nanoparticles (NPs) and thin films. In situ X-ray diffraction patterns were acquired as a function of temperature, where the positions and widths of the diffraction peaks were systematically tracked upon heating and cooling down to room temperature (RT). Scanning electron microscopy provides physical insight on the CsPbBr3 thin films upon annealing and transmission electron microscopy gives physical and crystallographic information for the CsPbBr3 NPs using electron diffraction. The secondary phase(s) CsPb2Br5 (and CsPb4Br6) are clearly observed in the XRD patterns of both nanoparticles and thin films upon heating to 500 K, whilst from 500 K to 595 K, these phases remain in small amounts and are kept like this upon cooling down to RT. However, in the case of thin films, the CsPb2Br5 secondary phase disappears completely above 580 K and pure cubic CsPbBr3 is observed up to 623 K. The CsPbBr3 phase is then kept upon cooling down to RT, achieving pure CsPbBr3 phase. This study provides detailed understanding of the phase behavior vs. temperature of CsPbBr3 NPs and thin films, which opens the way to pure CsPbBr3 phase, an interesting material for optoelectronic applications

Detectability, Invasiveness and the Quantum Three Box Paradox

Quantum pre- and post-selection (PPS) paradoxes occur when counterfactual inferences are made about different measurements that might have been performed, between two measurements that are actually performed. The 3 box paradox is the paradigm example of such a paradox, where a ball is placed in one of three boxes and it is inferred that it would have been found, with certainty, both in box 1 and in box 2 had either box been opened on their own. Precisely what is at stake in PPS paradoxes has been unclear, and classical models have been suggested which are supposed to mimic the essential features of the problem. We show that the essential difference between the classical and quantum pre- and post-selection effects lies in the fact that for a quantum PPS paradox to occur the intervening measurement, had it been performed, would need to be invasive but non-detectable. This invasiveness is required even for null result measurements. While some quasi-classical features (such as non-contextuality and macrorealism) are compatible with PPS paradoxes, it seems no fully classical model of the 3 box paradox is possible.Comment: 16 pages, no figure