Published in Physical Review A: Experimental quantum key distribution with simulated ground-to-satellite photon losses and processing limitations

Fundamental laws of quantum physics guarantee the security of encryption keys generated through quantum key distribution, in contrast to standard encryption techniques which rely on assumptions about an eavesdropper's computational ability. That said, special technology is necessary to facilitate quantum key distribution transmissions between parties that are more than a couple of hundred kilometers apart.

A near-term solution is to use an orbiting satellite as a trusted quantum receiver. Here we detail specifically chosen algorithms that make up an implementation of quantum key distribution, suitable for a satellite receiver platform. We examine these algorithms' computational requirements while demonstrating them experimentally as we emulate the variable channel losses that would be experienced during a satellite pass (following those we published about previously).

J.-P. Bourgoin, N. Gigov, B. L. Higgins, Z. Yan, E. Meyer-Scott, A. K. Khandani, N. Lütkenhaus, and T. Jennewein

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Hey look-it, I'm on the TV!

So it seems my face has now graced (or disgraced, perhaps) North American television. Some folks from DMG Productions were in the lab a while ago gathering footage for a segment on IQC for Innovations with Ed Begley, Jr. Though my supervisor fielded the actual spoken material, you can spot me in the background of various “action shots” discussing clearly very important things™ with students and colleagues.

Here's the segment in question, first broadcast on Discovery Channel, May 25, 2015.

I've similarly been on Australian TV before, so that makes two continents that have had to deal with my mug on air.

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Published in Physical Review A: Using weak values to experimentally determine “negative probabilities” in a two-photon state with Bell correlations

It's well known that quantum entangled systems can exhibit correlations that go beyond those that could be seen if Nature worked in intuitive “classical” ways. However, as Richard Feynman noted, classical theory can support exhibiting such correlations if we invoke negative probabilities to describe their properties. What he did not do was specify how these negative probabilities ought to be chosen, and without any justification, an infinite number of different combinations could be chosen that will satisfy the relevant equations.

The concept of negative probabilities seems nonsensical because they cannot actually be observed—indeed, they cannot be observed even within the framework of quantum theory due to the effects of measurement back-action. Here, we show how they can instead be inferred through the use of weak measurements, where a meter is only weakly coupled to the property of interest, thereby avoiding the back-action problem. Each individual weak measurement has a …

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Published in Nature Photonics: Experimental three-photon quantum nonlocality under strict locality conditions

Quantum mechanics implies properties of Nature that clash with our intuitive notions of how the universe ought to work. Testing these properties (to see if quantum mechanics is, indeed, true) involves generating entangled quantum states of two or more particles and measuring them under a number of strict conditions. While work is progressing to meet all of these conditions when using only two particles, no one has yet met even one of these conditions for more than two particles, which is considerably more difficult experimentally. Here, we conduct an experiment where we meet two of the most challenging conditions—namely measurement locality and freedom of choice—while generating triplet entangled photon states. We demonstrate that quantum mechanics wins out over intuition, measuring a violation of Mermin's inequality outside the classical bound by nine standard deviations.

C. Erven, E. Meyer-Scott, K. Fisher, J. Lavoie, B. L. Higgins, Z. Yan, C. J …

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Adding the binary entropy function to LibreOffice Calc

Lately at work I've been doing some data analysis in LibreOffice Calc that requires the binary entropy function. The function itself looks like H2(x) =  − xlog2(x) − (1 − x)log2(1 − x), where 0log2(0) is taken to be 0. It's this latter point that makes things a little tricky. LibreOffice Calc doesn't have this function built-in, sadly, and you have to explicitly guard for the case where x is 0 or 1, which is not easy to pull off inside a cell.

So I wrote a basic macro that implements it:

Function BINENT(x)
    If x = 0 Or x = 1 Then
        BINENT = 0
    ElseIf x > 0 And x < 1 Then
        BINENT = -(x*Log(x) + (1 - x)*Log(1 - x))/Log(2)
    Else
        BINENT = Null
    End If
End Function

To be able to use BINENT in Calc, go to the “Tools” menu, “Macros”, “Organize Macros …

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Published in Optics Express: Generating polarization-entangled photon pairs using cross-spliced birefringent fibers

Generating entangled photon states is vital for numerous quantum communications and quantum computation primitives. Here we pioneer a new approach to in-fiber generation of entangled photon pairs. We take inspiration from a technique in bulk-optics, where two nonlinear crystals are sandwiched close together, and splice two pieces of birefringent optical fiber together at 90 degree orientation. With suitable compensation optics, all of which could be implemented in fiber, we show fidelity with a maximally-entangled Bell state of better than 92%.

E. Meyer-Scott, V. Roy, J.-P. Bourgoin, B. L. Higgins, L. K. Shalm, and T. Jennewein
Optics Express 21, 6205–12 (2013)

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