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Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE

Non-destructive quantum measurement scheme for quantum states in superposition

Patrick D. Kumavor, Eric Donkor

Published Mar 26, 2008• 0 citations
Publisher

Abstract

The measurement of discrete quantum systems is a vital ingredient for quantum information processors. These systems, being fragile in nature, are characterized by a perturbation or collapse of their states whenever they are measured due to measurement-induced decoherence. We propose a quantum measurement model that allows for the extraction of information from any superposed quantum system without inducing a total collapse. The methodology used involves the coupling of a quantum probe through suitable interactions that create a partial entanglement between probe and quantum system. This entanglement in turn transfers information about the quantum system to the probe. Therefore, by making measurements on the probe rather than the superposed quantum system itself, we avert a total collapse to the quantum system.

DOI
10.1117/12.779456

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The measurement of discrete quantum systems is a vital ingredient for quantum information processors. These systems, being fragile in nature, are characterized by a perturbation or collapse of their states whenever they are measured due to measurement-induced decoherence. We propose a quantum measurement model that allows for the extraction of information from any superposed quantum system without inducing a total collapse. The methodology used involves the coupling of a quantum probe through suitable interactions that create a partial entanglement between probe and quantum system. This entanglement in turn transfers information about the quantum system to the probe. Therefore, by making measurements on the probe rather than the superposed quantum system itself, we avert a total collapse to the quantum system.
The measurement of discrete quantum systems is a vital ingredient for quantum information processors. These systems, being fragile in nature, are characterized by a perturbation or collapse of their states whenever they are measured due to measurement-induced decoherence. We propose a quantum measurement model that allows for the extraction of information from any superposed quantum system without inducing a total collapse. The methodology used involves the coupling of a quantum probe through suitable interactions that create a partial entanglement between probe and quantum system. This entanglement in turn transfers information about the quantum system to the probe. Therefore, by making measurements on the probe rather than the superposed quantum system itself, we avert a total collapse to the quantum system. Our measurement model is applied to quantum computers for the measurement of their superposed states. The use of the measurement scheme for solving computational problems on the quantum computer is presented. In addition, the measurement scheme is invoked as an eavesdropping scheme on quantum cryptography systems; we show the degree to which their security is comprised. Lastly, the system performance of multi-user quantum cryptography networks is simulated, culminating in the experimental demonstration of a six-user quantum cryptographic network system. ^
Abstract In the context of the century-long debate on quantum measurement problem, the current work proposes a model that describes the process of collapse of state by quantum interaction, which resolves the controversies of the framework of quantum mechanics and describes the entire domain of quantum-to-classical world including the weak measurement and partial collapse. ‘Measurement’, being the process of physically interacting with a system in order to extracting information from it, is theorized in the current model by synthesizing the quantum interaction between system and measuring apparatus with the information entropy of such process. The model assumes Schrödinger equation to be the only guiding equation for all physical systems including the measuring apparatus, and does not presuppose ‘superposition principle’, rather derives it theoretically from the formulation. The superposed state is shown to be independent of the choice of measurement operator (observable) or basis states (pointers) of the measuring apparatus. Most interestingly, the current model explains the non-observance of ‘superposition principle’ by classical systems as the classical limit of such quantum description of measurement. Along with solving the quantum measurement problem, the work also explains weak measurement and partial collapse, which can be further extended to investigate such several emerging critical phenomena.
Abstract In the context of the century-long debate on quantum measurement problem, the current work proposes a model that describes the process of collapse of state by quantum interaction, which resolves the controversies of the framework of quantum mechanics and describes the entire domain of quantum-to-classical world including the weak measurement and partial collapse. ‘Measurement’, being the process of physically interacting with a system in order to extracting information from it, is theorized in the current model by synthesizing the quantum interaction between system and measuring apparatus with the information entropy of such process. The model assumes Schrödinger equation to be the only guiding equation for all physical systems including the measuring apparatus, and does not presuppose ‘superposition principle’, rather derives it theoretically from the formulation. The superposed state is shown to be independent of the choice of measurement operator (observable) or basis states (pointers) of the measuring apparatus. Most interestingly, the current model explains the non-observance of ‘superposition principle’ by classical systems as the classical limit of such quantum description of measurement. Along with solving the quantum measurement problem, the work also explains weak measurement and partial collapse, which can be further extended to investigate such several emerging critical phenomena.
Decoherence, often caused by unavoidable coupling with the environment, leads to degradation of quantum coherence. For a multipartite quantum system, decoherence leads to degradation of entanglement and, in certain cases, entanglement sudden death. Tackling decoherence, thus, is a critical issue faced in quantum information, as entanglement is a vital resource for many quantum information applications including quantum computing, quantum cryptography, quantum teleportation, and quantum metrology. Here, we propose and demonstrate a novel scheme to protect entanglement from decoherence. Our entanglement protection scheme makes use of the quantum measurement itself for actively battling against decoherence and it can effectively circumvent even entanglement sudden death (ESD).
A quantum measurement process, when non-trivial, is not a closed evolution: the appearance of classical outcomes is usually interpreted as the evidence of some decoherence-like mechanism causing quantum superpositions to degrade into classical mixtures. Such mechanism is due to a net flow of information from the input system (measurement object), through the physical apparatus interacting with the object (measurement probe), into some environment, the latter representing all those degrees of freedom which are not directly accessible by the experimenter. For this reason, the phenomenon of state reduction induced by the measurement process generally entails an irreversible state change. The aim of our contribution is to answer the following questions : how much information a measurement is able to extract? "How much" irreversible is the state reduction due to a particular measurement process? In which way information gain and irreversibility are related?