We present and experimentally show a novel protocol for distributing secret information between two and only two parties in a N-party single-qubit Quantum Secret Sharing (QSS) system. We demonstrate this new algorithm with N = 3 active parties over ~6km of telecom. fiber. Our experimental device is based on the Clavis<sup>2</sup> Quantum Key Distribution (QKD) system built by ID Quantique but is generalizable to any implementation. We show that any two out of the N parties can build secret keys based on partial information from each other and with collaboration from the remaining N − 2 parties. This algorithm allows for the creation of two-party secret keys were standard QSS does not and significantly reduces the number of resources needed to implement QKD on a highly connected network such as the electrical grid.
Proc. SPIE. 9500, Quantum Information and Computation XIII
KEYWORDS: Clocks, Modulation, Photons, Single photon, Field programmable gate arrays, Quantum key distribution, Single photon detectors, Signal detection, Quantum information, Global Positioning System
We demonstrate a quantum time distribution (QTD) method that combines the precision of optical timing techniques with the integrity of quantum key distribution (QKD). Critical infrastructure is dependent on microprocessor- and programmable logic-based monitoring and control systems. The distribution of timing information across the electric grid is accomplished by GPS signals which are known to be vulnerable to spoofing. We demonstrate a method for synchronizing remote clocks based on the arrival time of photons in a modified QKD system. This has the advantage that the signal can be verified by examining the quantum states of the photons similar to QKD.
Quantum Key Distribution (QKD) exploits the rules of quantum mechanics to generate and securely distribute a random
sequence of bits to two spatially separated clients. Typically a QKD system can support only a single pair of clients at a
time, and so a separate quantum link is required for every pair of users. We overcome this limitation with the design and
characterization of a multi-client entangled-photon QKD system with the capacity for up to 100 clients simultaneously.
The time-bin entangled QKD system includes a broadband down-conversion source with two unique features that enable
the multi-user capability. First, the photons are emitted across a very large portion of the telecom spectrum. Second, and
more importantly, the photons are strongly correlated in their energy degree of freedom. Using standard wavelength
division multiplexing (WDM) hardware, the photons can be routed to different parties on a quantum communication
network, while the strong spectral correlations ensure that each client is linked only to the client receiving the
conjugate wavelength. In this way, a single down-conversion source can support dozens of channels simultaneously--and
to the extent that the WDM hardware can send different spectral channels to different clients, the system can support
multiple client pairings. We will describe the design and characterization of the down-conversion source, as well as the
client stations, which must be tunable across the emission spectrum.
Spontaneous parametric down-conversion (SPDC) is a reliable and robust source of photons for quantum
information applications. For applications that involve operations such as entanglement swapping or single-photon
heralding, two-photon states are required to be factorable (uncorrelated) in their spectral and spatial degrees of
freedom. We report the design and experimental characterization of an SPDC source that has been optimized for
high spectral and spatial purity. The source is pumped by the 776 nm output of a mode-locked Ti:Sapphire laser and
consists of a periodically-poled Potassium Titanyl Phosphate (PPKTP) crystal phase-matched for collinear type-II
SPDC. The dispersive properties of PPKTP at these wavelengths is such that it is possible to minimize the spectral
entanglement by matching the widths of the pump to the spectral phase-matching function. The spatial entanglement
is minimized through careful control of the pump focus, yielding nearly single-mode emission. An advantage of this
approach is that the emission rate into the collection modes is very high, resulting in a very bright SPDC source. We
also report a scheme that employs the output of collinear sources such as these to produce polarization-entangled
photon pairs. The scheme, which requires only simple polarization elements, can be scaled to N-photon GHZ states.
Spectral correlations between photon pairs generated by spontaneous parametric down conversion (SPDC) in
bulk non-linear optical crystals remain a hindrance to the implementation of efficient quantum communication
architectures. It has been demonstrated that SPDC within a distributed micro-cavity can result in little or no
correlation between photon pairs. We present results on modeling three different cavity configurations based
on integrated Bragg gratings. Output from the SPDC process can be tailored by altering the periodicity and
geometry of such nanostructures. We will discuss the merits of each cavity configuration from the standpoint of
degenerate type-II SPDC.