Here we detail our work on optoelectronics implementing a high-speed high-fidelity source of optical quantum states for quantum encryption.
We perform a thorough theoretical analysis of the expected key rate, success of Bell test, and teleportation distance of experiments performed between the ground and a satellite in low Earth orbit. Our findings demonstrate that successful, regularly repeatable demonstrations are feasible with current technologies and relatively small telescopes.
An ensemble cast detail the new physics that could be explored by taking quantum optics experiments into space. My first publication as part of Prof. Thomas Jennewein's group, I contributed details about near-term tests and our present work at the Institute for Quantum Computing, and helped out with logistics and proofing.
Following on from our prior paper, here we take a closer theoretical look at the different measurement approaches one can use to discriminate between nonorthogonal quantum states when given multiple copies. We examine the behaviour of these schemes in both limits of moderate number of copies and as the number of copies tends towards infinity (the latter of which took quite a long time to determine for the overall optimal scheme), and we identify the quantum mixture regimes in which certain measurements become the same. Indeed, we show that for more than 2% mixture and a large number of copies, the naive measurement strategy is as good as any other.
Here we take our knowledge of adaptive quantum control and apply it to enhance phase measurement when we are given a limited set of entangled quantum states. We show the measurement of a completely unknown phase at precision that is in principle below the limit of standard techniques.
It's known to be impossible to, with 100% accuracy, discriminate between two different quantum states that are not orthogonal. In this paper we look at how accurately you can make this determination when you are given multiple identical copies of one of the two nonorthogonal states. We consider different measurements you can perform, and find that a measurement strategy that performs optimally when the states in question are pure actually performs poorer than a naive “majority vote” scheme when the states have some mixture. We experimentally demonstrate these schemes and derive (and also demonstrate) an adaptive measurement scheme that performs optimally in all conditions, and compare it to the fundamental limit.
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