Secure quantum key distribution (QKD) is limited by the Earth’s horizon, weather, and turbulence in the atmosphere. We will outline the analysis, design, and early stages of our mobile small unmanned aircraft system (sUAS) free-space optical quantum communication system. This reconfigurable, quantum-secure communication platform can potentially open up a novel communication layer that can avoid local weather interruptions as well as provide a substantial reduction in turbulence-related loss by transmitting above ground level. We review the design and testing of a custom cage-system mode analyzer to be implemented as the receiving optics module on a sUAS. The tests of our design, within predicted operational parameters, suggests that this is a feasible option for a mode analyzer on a light-weight mobile platform.
We discuss the properties of quantum state reactivity as a measure for quantum correlation. This information geometry-based definition is a generalization of the two qubit construction of Schumacher to multipartite quantum states. It requires a generalization of information distance to information areas as well as to higher-dimensional volumes. The reactivity is defined in the usual chemistry way as a ratio of surface area to volume. The reactivity is an average over all detector settings. We show that this measure posses the key features required for a measure of quantum correlation. We show that it is invariant under local unitary transformations, non{increasing under local operations and classical communication, and monotonic. Its maximum bound can't be obtained using only classical correlation. Furthermore, reactivity is an analytic function of measurement probabilities and easily extendable to higher multipartite states.
A photon with a modulated wavefront can produce a quantum communication channel in a larger Hilbert space. For example, higher dimensional quantum key distribution (HD-QKD) can encode information in the transverse linear momentum (LM) or orbital angular momentum (OAM) modes of a photon. This is markedly different than using the intrinsic polarization of a photon. HD-QKD has advantages for free space QKD since it can increase the communication channels tolerance to bit error rate (BER) while maintaining or increasing the channels bandwidth. We describe an efficient numerical simulation of the propagation photon with an arbitrary complex wavefront in a material with an isotropic but inhomogeneous index of refraction. We simulate the waveform propagation of an optical vortex in a volume holographic element in the paraxial approximation using an operator splitting method. We use this code to analyze an OAM volume-holographic sorter. Furthermore, there are analogue models of the evolution of a wavefront in the curved spacetime environs of the Earth that can be constructed using an optical medium with a given index of refraction. This can lead to a work-bench realization of a satellite HD-QKD system.
We introduce a new approach to evaluating entangled quantum networks using information geometry. Quantum computing is powerful because of the enhanced correlations from quantum entanglement. For example, larger entangled networks can enhance quantum key distribution (QKD). Each network we examine is an n-photon quantum state with a degree of entanglement. We analyze such a state within the space of measured data from repeated experiments made by n observers over a set of identically-prepared quantum states – a quantum state interrogation in the space of measurements. Each observer records a 1 if their detector triggers, otherwise they record a 0. This generates a string of 1’s and 0’s at each detector, and each observer can define a binary random variable from this sequence. We use a well-known information geometry-based measure of distance that applies to these binary strings of measurement outcomes,1–3 and we introduce a generalization of this length to area, volume and higher-dimensional volumes.4 These geometric equations are defined using the familiar Shannon expression for joint and mutual entropy.5 We apply our approach to three distinct tripartite quantum states: the |GHZi state, the |Wi state, and a separable state |Pi. We generalize a well-known information geometry analysis of a bipartite state to a tripartite state. This approach provides a novel way to characterize quantum states, and it may have favorable scaling with increased number of photons.
In our earlier work we posited that simple quantum gates and quantum algorithms can be designed utilizing the diffraction phenomena of a photon within a multiplexed holographic element. The quantum eigenstates we use are the photons transverse linear momentum (LM) as measured by the number of waves of tilt across the aperture. Two properties of linear optical quantum computing (LOQC) within the circuit model make this approach attractive. First, any conditional measurement can be commuted in time with any unitary quantum gate; and second, photon entanglement can be encoded as a superposition state of a single photon in a higher-dimensional state space afforded by LM. We describe here our experimental results for construction a controlled NOT (CNOT) gate logic within a holographic medium, and present the quantum state tomography for this device. Our theoretical and numerical results indicate that OptiGrates photo-thermal refractive (PTR) glass is an enabling technology. This work has been grounded on coupled-mode theory and numerical simulations, all with parameters consistent with PTR glass. We discuss the strengths (high efficiencies, robustness to environment) and limitations (scalability, crosstalk) of this technology. While not scalable, the utility and robustness of such optical elements for broader quantum information processing applications can be substantial.
Quantum gates and simple quantum algorithms can be designed utilizing the diffraction phenomena of a photon
within a multiplexed holographic element. The quantum eigenstates we use are the photon's linear momentum
(LM) as measured by the number of waves of tilt across the aperture. Two properties of quantum computing
within the circuit model make this approach attractive. First, any conditional measurement can be commuted in
time with any unitary quantum gate - the timeless nature of quantum computing. Second, photon entanglement
can be encoded as a superposition state of a single photon in a higher-dimensional state space afforded by LM. Our
theoretical and numerical results indicate that OptiGrate's photo-thermal refractive (PTR) glass is an enabling
technology. We will review our previous design of a quantum projection operator and give credence to this
approach on a representative quantum gate grounded on coupled-mode theory and numerical simulations, all with
parameters consistent with PTR glass. We discuss the strengths (high efficiencies, robustness to environment)
and limitations (scalability, crosstalk) of this technology. While not scalable, the utility and robustness of such
optical elements for broader quantum information processing applications can be substantial.
Bell's theorem, and inequalities that stem from it, address the conflict between the explanation of key experimental
observations by quantum mechanics (QM) and by models expressing Locally Realistic (LR) properties, regardless of
their inclusion or exclusion of hidden variables. To demonstrate the conflict between experimental results described by
QM and LR models, a physical realization of the quantum state must be chosen. Entangled photons or electrons provide
the most viable choices. In this work we consider a simplified version of a Bell inequality (BI) that focuses entirely on
the physical state properties of photons in order to demonstrate the difference between QM and LR correlations. While
the experiment we propose is in principle similar in intent to prior Bell inequality experiments, our version requires
fewer measurements, and is more advantageous in its conceptual clarity.
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