Time as a resource in integrated quantum photonics

  • Patrick W Yard

Student thesis: Doctoral ThesisDoctor of Philosophy (PhD)

Abstract

Photonics, as a platform for quantum information processing, has the unique ability to exploit the qubits temporal degree of freedom. For photonic quantum computing, this can be used to conserve physical resources by encoding photonic qubits directly in the temporal degree of freedom thereby allowing a quantum processor with a modest physical footprint to operate in a large Hilbert space. Additionally, through the conjugate relationship of time and frequency in quantum optics, the bandwidth of photons is related to the timing resolution of detectors, thereby allowing a route to increase the visibility of quantum interference between photons of differing frequency. Conversely, the role of time itself in quantum mechanics can be explored through the mapping of unitary dynamics to photonic quantum simulators where time is a programmable parameter. In this thesis, we explore each of these aspects of time, through a series of quantum photonics experiments including in integrated quantum photonic technologies.

Initially, we see how increasing the timing resolution of quantum interference experiments can lead to new interference effects. We use a silicon chip to perform both HOM interference and interference in a Fourier interferometer. In both cases, we show that decreasing the timing window of the experiment leads to an increase in the visibility of the interference fringes. Following this, we apply this technique to two photon scattershot boson sampling. To combat the inherent reduction in sample rate that accompanies temporal filtering, we perform boson sampling experiments by sampling directly from the photon's arrival time for both two (four detected) and three (six detected) photons. Next, we look at simulating, designing and testing a high-speed all-optical switch, based on inter-modal cross-phase modulation, in silicon nitride. Here, the signal and pump fields propagate in the fundamental and first order transverse electric modes, respectively. We show first devices with a phase shift of up to 0.94 rads and show how our simulations match the results closely, giving us confidence that we can reach pi phase shifts with future devices. Finally, we look at how integrated photonics can be used to simulate the dynamics of Hamiltonians that are non-Hermitian, but symmetric under combined parity and time reversal. Using a silica chip, capable of implementing arbitrary unitary transformations on up to six modes, we simulate the non-unitary dynamics of these systems. Experimentally, we use a time-varying Hamiltonian, implemented by an adaptive feedback loop, to increase the coherence of a target qubit. In simulation, we more rigorously test the algorithm and compare to a fixed Hamiltonian.

These results provide insight into the benefits of exploiting the temporal degree of freedom in quantum photonic experiments and provide evidence for the feasibility and scalability of integrated quantum photonics.
Date of Award2 Dec 2021
Original languageEnglish
Awarding Institution
  • University of Bristol
SupervisorAnthony Laing (Supervisor) & Alexander Jones (Supervisor)

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