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Scaling Photonic Quantum Computers Scaling photonic quantum computers ZACHARY VERNON University of Pavia Colloquium 29 April 2021 Copyright © 2021 Xanadu Quantum Technologies Inc. OUTLINE 1. ABOUT US 4. APPLICATIONS: NISQ AND FTQC 2. PHOTONICS FOR QUANTUM COMPUTING 5. NANOPHOTONIC DEVICES FOR SQUEEZING 3. GAUSSIAN BOSON SAMPLING ON THE CLOUD Copyright © 2021 Xanadu Quantum Technologies Inc. ABOUT XANADU CEO HARDWARE SOFTWARE ARCHITECTURE PRODUCT Christian Weedbrook, PhD Zachary Vernon, PhD Nathan Killoran, PhD Ish Dhand, PhD Rafal Janik, MSc Founded in 2016 | HQ in Toronto | 70+ people | 40+ PhDs | 15+ nationalities Advisors: Founded in 2016 Funding: $45M Office & Hardware Lab in Toronto Copyright © 2021 Xanadu Quantum Technologies Inc. 3 PHOTONICS FOR QUANTUM COMPUTING: MATTER VS LIGHT-BASED QUBITS Requirements What makes a qubit? 1. A scalable physical system with well DiVincenzo criteria, 2000: characterized qubit 2. The ability to initialize the state of the qubits to a simple fiducial state 3. Long relevant decoherence times 4. A "universal" set of quantum gates 5. A qubit-specific measurement capability Fortschr. Phys.4892000) 9-11, 771-783 Desiderata 1. The ability to interconvert stationary and flying qubits 2. The ability to faithfully transmit flying qubits between specified locations Copyright © 2021 Xanadu Quantum Technologies Inc. 4 PHOTONICS FOR QUANTUM COMPUTING: MATTER VS LIGHT-BASED QUBITS Requirements 1. A scalable physical system with well Trapped ions Superconducting electronics characterized qubit 2. The ability to initialize the state of the qubits to a simple fiducial state 3. Long relevant decoherence times 4. A "universal" set of quantum gates 5. A qubit-specific measurement capability Source: Physics World Source: Phys.org Desiderata 1. The ability to interconvert At the time (c. 2000), matter-based qubits were stationary and flying qubits generally assumed to be the only option 2. The ability to faithfully transmit flying qubits between specified Blocker: Lack of single-photon level nonlinearity locations Copyright © 2021 Xanadu Quantum Technologies Inc. 5 PHOTONICS FOR QUANTUM COMPUTING: MATTER VS LIGHT-BASED QUBITS “KLM” protocol for photonic quantum computing, 2001: Nature volume 409, pages 46–52(2001) Showed that photonic QC was, in principle, possible without exotic photon-photon interactions. Tradeoff: Lack of deterministic operation, leading to huge component counts. Copyright © 2021 Xanadu Quantum Technologies Inc. 6 PROS AND CONS OF PHOTONICS Photonics Superconducting Trapped ions Operating Mostly room temperature, no Cryostat @ 10mK Vacuum chamber, laser vacuum cooling to nK environment Chip integration Compatible with standard Specialized Cannot be fully chip CMOS fabs research/university fabs integrated Prospects for scaling Modularity via telecom No suitable interconnect yet Optical interconnect using fiber-optic interconnects demonstrated UV/visible photonic elements Maturity of industry Benefits from optical telecom Small market for Very little market for industry components superconducting electronics components outside for components in other applications scientific research Bandwidth/clock Ultrahigh bandwidth: GHz kHz reset rates, gates can be Slow reset times and gate possible reasonably fast speeds speeds Copyright © 2021 Xanadu Quantum Technologies Inc. 7 PROS AND CONS OF PHOTONICS Photonics Superconducting Trapped ions Platform simplicity Difficult to do everything in Qubits, gates, measurements Complicated laser control one material platform, need done in same layer, control (many UV/visible beams heterogeneous and readout done with RF required) integration/multi-chip pulses architecture Component counts Large due to Moderate, but wiring inside Low, also due to high non-deterministic elements cryostat is a serious challenge fidelities allowing possibly (cryoCMOS required?) lower overheads for fault tolerance Copyright © 2021 Xanadu Quantum Technologies Inc. 8 THE CASE FOR PHOTONICS FASTER UNIQUE LOWER SCALABLE NETWORK + + + + DEVELOPMENT ENCODING COST & MODULAR COMPATIBLE Much faster Different NISQ applications Fiber interconnects Can borrow many tools from Natural interface with prototyping cycles due to room and more ways to implement distribute qubits across optical telecom industry future quantum internet temperature QPUs error correction many chips Copyright © 2021 Xanadu Quantum Technologies Inc. 9 XANADU’S ROADMAP TO UNIVERSAL QUANTUM COMPUTING NISQ GATE-BASED SYSTEMS GAUSSIAN Xanadu’s BOSON GKP QUBITS approach SAMPLING UNIVERSAL FAULT-TOLERANT QUANTUM COMPUTER Other approaches VQE QAOA Time Copyright © 2021 Xanadu Quantum Technologies Inc. 10 PHOTONIC QUANTUM COMPUTING ON THE CLOUD Copyright © 2021 Xanadu Quantum Technologies Inc. 11 GAUSSIAN BOSON SAMPLING The formula Squeezed states (single temporal mode) + Linear optics = (programmable, phase stable) + Photon counting (photon number resolving) Source: “Applications of near-term photonic quantum computers: Software and algorithms”, T.R. Bromley et al., Quantum Science and Technology (2020) Copyright © 2021 Xanadu Quantum Technologies Inc. 12 GAUSSIAN BOSON SAMPLING Source: Science 18 Dec 2020: Vol. 370, Issue 6523, pp. 1460-1463 Source: “Applications of near-term photonic quantum computers: Software and algorithms”, T.R. Bromley et al., Quantum Science and Technology (2020) Copyright © 2021 Xanadu Quantum Technologies Inc. 13 NANOPHOTONIC BUILDING BLOCKS Input: Compiled program loaded to chip via DACs Pulsed pump laser source Output: Programmable 8-mode entangled Squeezed Programmable interferometer Gaussian state light sources (Information encoding and quantum gate sequence) Copyright © 2021 Xanadu Quantum Technologies Inc. 14 GAUSSIAN BOSON SAMPLING ON A CHIP Equivalent quantum circuit Copyright © 2021 Xanadu Quantum Technologies Inc. 15 CONTROL SYSTEM (SIMPLIFIED) Input / Output Master Controller (Sends and receives classical information to the various components) User Interface & Remote Access (Xanadu’s Strawberry Fields software) Laser pump Chip control system (optical source) (DACs to encode information) QPU Data acquisition system Xanadu’s 1st generation chip Photon Number Resolving Detectors (via NIST) Copyright © 2021 Xanadu Quantum Technologies Inc. 16 SQUEEZER PERFORMANCE Single-squeezer statistics Two-squeezer interference Copyright © 2021 Xanadu Quantum Technologies Inc. 17 GAUSSIAN BOSON SAMPLING: NEAR-TERM APPLICATIONS DENSE MAXIMUM POINT SUBGRAPH CLIQUE PROCESS QUANTUM GRAPH VIBRONIC ENHANCED SIMILARITY SPECTRA FEATURE “Applications of near-term photonic quantum TUTORIALS AVAILABLE AT STRAWBERRYFIELDS.AI computers: Software and algorithms”, T.R. Bromley et al., Quantum Science and Technology (2020) Copyright © 2021 Xanadu Quantum Technologies Inc. 18 GAUSSIAN BOSON SAMPLING WITH RANDOM PARAMETERS ● Randomized benchmark for device performance ● Compare experimental and theoretical distributions ● Good quantitative and qualitative agreement between experiment and theory Copyright © 2021 Xanadu Quantum Technologies Inc. 19 SIMULATION OF VIBRONIC SPECTRA ● Chemistry application unique to squeezing-based bosonic architecture ● Encode molecular structure directly in chip parameters Copyright © 2021 Xanadu Quantum Technologies Inc. 20 GRAPH SIMILARITY ● Graph-structured data encoded into X8 chip ● Readout statistics classify different graphs ● Clustering shows X8 can distinguish different graph structures Copyright © 2021 Xanadu Quantum Technologies Inc. 21 GBS FOR FAULT TOLERANT QUANTUM COMPUTING state factory multiplexer ● Architecture relies on GKP computational module qubits, enabling two layers of error correction p-squeezed state ● X8 chips are the building blocks for synthesizing GKP qubits ● Squeezed states help deal with non-deterministic GKP sources GKP state QPU Blueprint for a Photonic Fault-Tolerant Quantum Computer J. Eli Bourassa et al. Quantum 5, 392 (2021) Copyright © 2021 Xanadu Quantum Technologies Inc. 22 NANOPHOTONIC SOURCES OF SQUEEZED LIGHT Copyright © 2021 Xanadu Quantum Technologies Inc. 23 NANOPHOTONIC SQUEEZED LIGHT SOURCES Wish list for integrated squeezing platform & device Low confinement PPLN SiN OPOs above threshold SiN microring below threshold Nanophotonic system X ✓ ✓ Quadrature squeezing ✓ X ✓ Photon counting compatible ✓ X ✓ Single temporal mode ? X ✓ No excess noise ✓ X ✓ Lenzini et al., Sci. Adv. 4, eaat9331 (2018) Dutt et al., Phys. Rev. Vaidya et al., Sci. Adv. eaba9186 (2020) Applied 3, 044005 (2015) Zhang et al., Nat. Comm. (2021) Copyright © 2021 Xanadu Quantum Technologies Inc. 24 NANOPHOTONIC MOLECULES FOR DEGENERATE SQUEEZING Zhang et al., “Squeezed Light from a Nanophotonic Molecule”Nature Communications (2021) Copyright © 2021 Xanadu Quantum Technologies Inc. NANOPHOTONIC MOLECULES FOR DEGENERATE SQUEEZING Record highest squeezing from a nanophotonic device! Similar setup to before, HNLF added to Similar setup to before, HNLF added to generate a tighter phase lock generate a tighter phase lock Zhang et al., “Squeezed Light from a Nanophotonic Molecule”Nature Communications (2021) Copyright © 2021 Xanadu Quantum Technologies Inc. Join us! Full-time positions available - xanadu.ai/careers [email protected] Copyright © 2021 Xanadu Quantum Technologies Inc. 27.
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