<p> In this dissertation, we describe, characterize, and demonstrate the operation of a dual-in, dual-out, all-optical, fiber-based quantum switch. This "cross-bar" switch is particularly useful for applications in quantum information processing because of its low-loss, high-speed, low-noise, and quantum-state-retention properties. </p><p> Building upon on our lab's prior development of an ultrafast demultiplexer <sup> [1-3]</sup> , the new cross-bar switch can be used as a tunable multiplexer <i> and</i> demultiplexer. In addition to this more functional geometry, we present results demonstrating faster performance with a switching window of ≈45 ps, corresponding to >20-GHz switching rates. We show a switching fidelity of >98%, i. e., switched polarization-encoded photonic qubits are virtually identical to unswitched photonic qubits. We also demonstrate the ability to select one channel from a two-channel quantum data stream with the state of the measured (recovered) quantum channel having >96% relative fidelity with the state of that channel transmitted alone. We separate the two channels of the quantum data stream by 155 ps, corresponding to a 6.5-GHz datastream. </p><p> Finally, we describe, develop, and demonstrate an application that utilizes the switch's higher-speed, lower-loss, and spatio-temporal-encoding features to perform quantum state tomographies on entangled states in higher-dimensional Hilbert spaces. Since many previous demonstrations show bipartite entanglement of two-level systems, we define "higher" as <i>d</i> > 2 where <i> d</i> represents the dimensionality of a photon. We show that we can generate and measure time-bin-entangled, two-photon, qutrit (<i>d</i> = 3) and ququat (<i>d</i> = 4) states with >85% and >64% fidelity to an ideal maximally entangled state, respectively. Such higher-dimensional states have applications in dense coding <sup>[4]</sup> , loophole-free tests of nonlocality <sup>[5]</sup> , simplifying quantum logic gates <sup> [6]</sup> , and increasing tolerance to noise and loss for quantum information processing <sup>[7]</sup> .</p>
| Identifer | oai:union.ndltd.org:PROQUEST/oai:pqdtoai.proquest.com:3669298 |
| Date | 29 January 2015 |
| Creators | Oza, Neal N. |
| Publisher | Northwestern University |
| Source Sets | ProQuest.com |
| Language | English |
| Detected Language | English |
| Type | thesis |
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