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Integrated quantum photonics for quantum applications

Xin Hua

Published Mar 29, 2021• 0 citations
Publisher

Abstract

This thesis reports an advanced monolithic integrated quantum photonic realization on lithium niobate, where nonlinear optics and electro-optics properties have been harnessed simultaneously for generating heralded configurable, two-photon states. Taking advantage of a picosecond pump laser and telecom components, we demonstrated the capability of producing various path-coded heralded two-photon, showing 94% raw visibility for Hong-Ou-Mandel (HOM) interference. The versatility and performance of such a highly integrated photonic entanglement source enable exploring more complex quantum information processing protocols finding application in communication, metrology and processing tasks. To enable on-chip two-photon interference, synchronization of two pump pulses entering the chip is crucial. Inspired by Young's double-slit experiment, we synchronize two pulses with a precision of 100 µm by investigating the interference-fringe contrast when varying the relative delay of the pulses. Using an autocorrelator and spectrometer, we determined the time-bandwidth product of the pump pulse and calculated the optimal filter bandwidth to obtain pure quantum states. Since the visibility of two-photon interference relates to the pump power, a theoretical investigation figuring out suitable pump power level was performed as well. In addition, the functionality of generating high quality two-photon path-entangled state was demonstrated by fourfold coincidence measurement relying on a four-channel superconducting single photon detector (SNSPD) and a programmable time-digital converter. In this thesis, the SNSPDs were calibrated and a logical counting algorithm based on Labview was developed to efficiently and accurately record the fourfold coincidences for N00N and product states.

DOI
10.70675/3612f15az45a3z4f3dz80dez7fabf7aa55ae

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This thesis reports an advanced monolithic integrated quantum photonic realization on lithium niobate, where nonlinear optics and electro-optics properties have been harnessed simultaneously for generating heralded configurable, two-photon states. Taking advantage of a picosecond pump laser and telecom components, we demonstrated the capability of producing various path-coded heralded two-photon, showing 94% raw visibility for Hong-Ou-Mandel (HOM) interference. The versatility and performance of such a highly integrated photonic entanglement source enable exploring more complex quantum information processing protocols finding application in communication, metrology and processing tasks. To enable on-chip two-photon interference, synchronization of two pump pulses entering the chip is crucial. Inspired by Young's double-slit experiment, we synchronize two pulses with a precision of 100 µm by investigating the interference-fringe contrast when varying the relative delay of the pulses. Using an autocorrelator and spectrometer, we determined the time-bandwidth product of the pump pulse and calculated the optimal filter bandwidth to obtain pure quantum states. Since the visibility of two-photon interference relates to the pump power, a theoretical investigation figuring out suitable pump power level was performed as well. In addition, the functionality of generating high quality two-photon path-entangled state was demonstrated by fourfold coincidence measurement relying on a four-channel superconducting single photon detector (SNSPD) and a programmable time-digital converter. In this thesis, the SNSPDs were calibrated and a logical counting algorithm based on Labview was developed to efficiently and accurately record the fourfold coincidences for N00N and product states.
Progress in integrated photonics enables the combination of several elementary functions on single substrates for the realization of advanced functionalized chips. We report a monolithic integrated quantum photonic realization on lithium niobate, where nonlinear optics and electro-optics properties have been harnessed simultaneously for generating heralded configurable, two-photon states. Taking advantage of a picosecond pump laser and telecom components, we demonstrate the production of various path-coded heralded two-photon states, showing 94% raw visibility for Hong-Ou-Mandel interference. The versatility and performance of such a highly integrated photonic entanglement source enable exploring more complex quantum information processing protocols finding application in communication, metrology and processing tasks.
A consequent tendency toward high-performance quantum information processing is to develop the fully integrated photonic chip. Here, we report the on-chip generation and manipulation of entangled photons based on reconfigurable lithium-niobate waveguide circuits. By introducing a periodically poled structure into the waveguide circuits, two individual photon-pair sources with a controllable electro-optic phase shift are produced within a Hong-Ou-Mandel interferometer, resulting in a deterministically separated identical photon pair. The state is characterized by 92.9±0.9% visibility Hong-Ou-Mandel interference. The photon flux reaches ∼1.4×10(7) pairs nm-1 mW-1. The whole chip is designed to contain nine similar units to produce identical photon pairs spanning the telecom C and L band by the flexible engineering of nonlinearity. Our work presents a scenario for on-chip engineering of different photon sources and paves the way to fully integrated quantum technologies.
Abstract Quantum photonic chip is a powerful platform to prepare multi-functional quantum light sources and actualize complex quantum information processing for its advantages of integration, stability, mass production, and reconfigurability. In this work, we design and fabricate a lithium niobate quantum photonic chip, consisting of tandem multi-poling structures, Mach-Zehnder interferometers, and electro-optic modulation, to produce multiple near-ideal quantum light sources including anti-bunching, path and frequency entangled photon pairs. The anti-bunching photon pairs exhibit off-chip Hong-Ou-Mandel interference visibilities above 99%. The fidelities of both frequency and path entanglement exceed 0.99. Meanwhile, all the quantum states hold a wide wavelength tuning range and high coupling efficiency from the chip. Our work paves the way for the development of programmable multi-functional quantum light sources and further promoting various quantum information tasks and enriching the architectures of on-chip quantum information processing.
Integrated quantum photonics furthers several quantum information protocols; one key feature of the on-chip setting is its potential for massively scalable quantum systems while operating with stability unseen in free-space optics. In this thesis, I develop theories, techniques, and sources to aid in developing potential future large-scale integrated quantum systems. A photon subtraction-based entanglement enhancement protocol for continuous-variable quantum networks is presented. The scheme shows that states generated with multiple single-mode squeezed input states, rather than a single input source, can be more sensitive to entanglement enhancement. To work toward implementing networks of squeezed light sources, an injection-locked pump laser for a spontaneous parametric downconversion (SPDC) process using a weak second harmonic generation signal is shown to be more power efficient compared to other conventional approaches. This injection-locking paradigm illustrates a novel approach to stabilize the phase of the pump of future integrated systems. Ideal quantum information platforms will achieve the integration of every element, including the pump. This thesis demonstrated the first battery-powered polarization-entangled photon source which was achieved using Bragg reflection waveguide laser diodes (BRLs). The output state with (without) accidentals subtracted from this device has a Bell-state fidelity of 98.0% (86.3%), a high brightness of 1.04*10^6 (pairs)/(s mW facet), and ultra-broadband entangled photon pairs, > 5.22 THz. I also adapted the BRLs to convert polarization-entanglement to time-energy entanglement with a visibility of 91%. Additionally, hyperentangled polarization and time-energy states with visibilities of 95.5% and 86% were demonstrated for the respective degrees of freedom after the subtraction of accidentals. The approach presented yields scalable, compact, low-power, stable, and room-temperature operated sources of polarization-entangled photons needed for quantum communications and network systems. Identical photon pairs allow for quantum interference of the photon states of interest. One important demonstration is the time-reversed Hong-Ou-Mandel (TRHOM) effect, which can achieve the deterministic separation of photon pairs. The BRLs presented in this work produce two outputs; hence, I demonstrate BRL with a TRHOM interference visibility of 89%. This TRHOM demonstration shows that BRLs are ideal candidates for current discrete variables and show future potential for continuous variable quantum information protocols.
Generating and interfering nonclassical states of light is fundamental to optical quantum information science and technology. Quantum photonic integrated circuits provide one pathway towards scalability by combining nonlinear sources of nonclassical light and programmable circuits in centimeter-scale devices. The key requirements for quantum applications include efficient generation of indistinguishable photon-pairs and high-visibility programmable quantum interference. Here, we demonstrate a lithium niobate-on-insulator (LNOI) integrated photonic circuit that generates a two-photon path-entangled state, and a programmable interferometer for quantum interference. We generate entangled photons with ∼2.3×10^{8} pairs/s/mW brightness and perform quantum interference experiments on the chip with 96.8±3.6% visibility. LNOI is an emerging photonics technology that has revolutionized high-speed modulators and efficient frequency conversion. Our results provide a path towards large-scale integrated quantum photonics including efficient photon-pair generation and programmable circuits for applications such as boson sampling and quantum communications.