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European Quantum Electronics Conference (EQEC)

Multiphoton quantum interference in multiport integrated optical circuits: from teleportation to Boson Sampling

Ian A. Walmsley, Benjamin J. Metcalf, Justin B. Spring, Peter C. Humphreys, Marco Barbieri, W. Steven Kolthammer, James C. Gates, Peter G. R. Smith

Published Jun 21, 2015• 1 citation
OpenAlex

Abstract

Building complex quantum systems has the potential to reveal new phenomena that cannot be studied using classical simulation. Photonics has proven to be an effective means to engineer quantum systems of this kind, and for the investigation of such effects. Scaling to large numbers of photons and components for their manipulation is facilitated by the compactness, inherent phase stability and simple alignment afforded by integrated photonic systems.

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•Jan 1, 2014•0 citations
Building complex quantum systems has the potential to reveal new phenomena that cannot be studied using classical simulation. Photonics has proven to be an effective means to engineer quantum systems of this kind, and for the investigation of such effects. Scaling to large numbers of photons and components for their manipulation is facilitated by the compactness, inherent phase stability and simple alignment afforded by integrated photonic systems.
It is strongly believed that the evolution of bosons undergoing arbitrary linear unitary transformations quickly becomes hard to predict using classical computers as we increase the number of particles and modes. Photons propagating in a multiport interferometer naturally solve this so-called boson sampling problem: sample the outputs of a multi-photon experiment in a linear-optical interferometer. This motivates the development of technologies that enable precise control of multiphoton interference in large interferometers.
Photonics is an effective platform for engineering quantum states of many photons that can be harnessed for applications in information processing tasks, ranging from secure communications to enhanced sensors to efficient simulation of physical or other systems. I will discuss recent developments and some challenges to achieving this promise. Building and measuring multi-photon quantum states suitable for these applications demands a means for them to interfere and for detection at the level of individual photons. Photonic integrated circuits are well suited to these tasks at a scale that is not possible by other means. Advances in the design and utilization of circuits and detectors enable quantum advantage, and indeed provide new opportunities for classical optical systems.
Quantum computing shows great potential in solving highly complex computational challenges in multiple applications, including artificial intelligence, chemical modelling, biology simulation, portfolio optimization, drug delivery, logistical planning, etc. Quantum networking can enable secure communication as well as scalable interconnects of multiple quantum processing units. We need to scale up the number of high-quality qubits and make quantum systems more compact, robust, and lower cost to further improve the performance of quantum computing and networking. Photonic integrated circuits (PICs) can play a significant role in reducing the size, improving the stability, and reducing the system bring-up time of optical subsystems. QuEra’s recent progress shows the potential of leveraging PICs as a viable solution to facilitate the builds of highly scalable and high-performance quantum computers [1]. These results position integrated photonics as a critical enabling technology for next-generation large-scale quantum systems and invite broader participation from the photonics community in advancing quantum technologies with significant industrial impact.
Quantum information science has shown that harnessing quantum mechanical effects can dramatically improve performance for certain tasks in communication, computation and measurement. Already a number of photonic quantum circuits have been realized for quantum metrology, lithography and quantum logic gates. However, these demonstrations have relied on large-scale (bulk) optical elements bolted to large optical tables, thereby making them inherently unscalable and confining them to the research laboratory. This paper reports on the implementation of quantum optic integrated circuits, which not only dramatically reduces the footprint of quantum circuits, but allows unprecedented stability and control of the optical path length; this reveals the possibility for realizing previously unfeasible large scale quantum circuits. Results from femtosecond laser directly-written quantum circuits are also discussed. A large range of chip-scale "photonic building blocks" have been realized using this so-called direct-write technique and they include multimode optical interconnects, directional couplers and interferometers. The directly written quantum circuits exhibited high 2 and 3-photon Hong-Ou-Mandel (HOM) interference visibilities of 95.8% plusmn 0.5 and 84% plusmn 3% respectively.
Building complex quantum systems has the potential to reveal phenomena that cannot be studied using classical simulation. Photonics has proven to be an effective test-bed for the investigation of such quantum-enhanced technologies, however, the proliferation of bulk optical components is unlikely to be a scalable route towards building more complex devices. Instead, the miniaturisation, inherent phase stability and trivial alignment afforded by integrated photonic systems has been shown to be a promising alternative. In the first half of this thesis, we describe experiments exploiting the quantum interference of three single photons on a reconfigurable integrated photonic chip. We develop a low-loss source of single photons and introduce a low-loss silica-on-silicon waveguide architecture which enables us to show the first genuine quantum interference of three single photons on an integrated platform. A loss-tolerant, element-wise characterisation scheme is developed along with a statistical test to verify that this multi-photon circuit behaves as expected. We then make use of this three-photon interference to detail the first proof-of-principle demonstration of a new intermediate model of quantum computation called boson sampling. Finally, we perform an on-chip demonstration of the quantum teleportation protocol where all key parts --- entanglement preparation, Bell-state analysis and quantum state tomography --- are performed on a reconfigurable photonic chip. The element-wise characterisation scheme developed earlier is shown to be critical to mitigate fabricated component errors. We develop a theoretical model to account for all sources of possible error in the circuit and find good agreement with the measured teleported state fidelities, which exceed the average teleportation fidelity possible with a classical device. We identify the elements of this error budget relevant to scaling and propose improvements to chip characterisation and fabrication in order to achieve high fidelity operation. In the second half, we discuss the use of high efficiency superconducting transition edge sensors in enabling quantum experiments using more photons. We detail the installation and characterisation of these detectors in a new lab in Oxford. We achieve good photon number-resolution and high-efficiency operation. Work to integrate these detectors on the silica-on-silicon waveguide architecture is discussed and we detail the optical and thermal device modelling performed to optimise the on-chip detection efficiency. New, on-chip detectors, fabricated according to this design are shown to operate as expected and achieve high-efficiency and good energy resolution.