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Quantum Computing and Quantum Supremacy John Martinis, Google the Quantum Space Race

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Quantum Computing and Quantum Supremacy John Martinis, Google the Quantum Space Race Quantum Computing and Quantum Supremacy John Martinis, Google The Quantum Space Race Hardware Challenges: Quantity Quality Quantum Data Quantum Data 2 Really Big Data n n=50: supercomputer n=300: more states than atoms in universe Bits and Qubits Classical bit: Quantum bit: 0 or 1 y cosq 0 sinq eif 1 Coin on table Coin in space Digital: self-correcting Analog: sensitive to small errors Any Logic Built from Universal Gates Classical circuit: Quantum circuit: 1 bit NOT 1 qubit rotation 2 bit AND 2 qubit CNOT Wiring fan-out -No copy- = |0 = y measurek Space (layout) Time (sequence) Full Digital (Clocked) Logic Classical system: Quantum system: D flip-flop aligns timing Error correction aligns to clock amplitude and phase each round, makes “quantum flip-flop” logic logic error clock correction (parity) Classical error decoding and logic 10-9 errors: 1000 qubits + 0.1% errors Need Both Quality and Quantity “error correction gain” “error 0.1 10-1 -2 1 10 Error correction threshold error rate error 10 10-3 10-9 errors miting i Classically L ✘ 100 simulatable 10-4 100 101 102 103 104 105 106 107 108 Number of Qubits Need Both Quality and Quantity “error correction gain” “error 0.1 10-1 quantity hype -2 1 10 Error correction threshold 1 error rate error 2 10 10-3 3 4 miting i Useful error Classically Near-term ✔ L ✘ ? corrected QC 100 simulatable applications 10-4 100 101 102 103 104 105 106 107 108 Number of Qubits 1: Quantum Supremacy 2: Look for near-term apps 3: Error correction Google strategy 4: Full QC Quality in Quantum Chemistry Experiments H2 Molecule LiH Molecule 2015 Google 0. 5% 2017 Brand 5% Brand 5% chemical No better than initial trial? accuracy 20x worse 1) Need low errors for accurate predictions Quality: 2) Need figure of merit for useful Xmon Transmon Qubit quantum circuit: Readout resonator 100 휇m mwaves (X,Y) AC drive Bus Self capacitance Variable L 6 GHz microwave oscillator Flux Bias (quantum: stabilize phase to 1 ps) Frequency (Z) Quantum vs. Classical-Supercomputer Challenge 50 qubits - checked with classical supercomputer Quantum Supremacy Algorithm: Qubit Speckle 1) Choose 1 instance, randomly from gateset d (time) Clifford Non-Clifford X, Z, H, X1/2… Z1/4 = |0 = qubits y n CZ measurek 2) Run quantum computer, measure k (2n possible outcomes) repeat sampling 100,000 times 1 s n (Random guess: any outcome k has probability pcl = 1/2 ) days 2 3) Calculate |y, p(k)= |k|y store in lookup table 200 drives 4) Correlation: cross entropy S = ln p(k)/pcl 5) Compare to theory Squ ≅ 0.42 quantum 6) Try another instance Scl ≅ -0.58 classical speckle = coherence predict = fidelity Compare probabilities of experiment and theory speckle pattern matches theory Measuring fidelity 0.3% error per gate & cycle Computing 500 states in parallel Quantum Materials (theory) 9 lattice sites 10000 T Quantum Materials (theory + experiment) “Bristlecone” Architecture Tile 2D grid of nearest neighbor coupled qubits, 72 total Bristlecone in test Huge Progress in Algorithms (Quantum Chemistry) universe 11 1985 Feynman (proposal) N N8 year N6 day N4 sec N2.7 N Exact: 100 logical qubits (error corrected) Approximate: 100 physical qubits (?) Huge Progress in Algorithms (Quantum Chemistry) universe 11 1985 Feynman (proposal) N N8 year N6 day N4 sec N2.7 N Useful QC now possible? Summary: Key Metrics UCSB: Google: 1) Quantity 9 72 2) Quality B: 0.55% limiting error best and average M: 0.75% 3) Speed 106 difference in technologies! 40 ns 4) Connectivity Error correction at least 2D 1D 2D Two Qubit Gate Errors (most critical) Google5 IBM20 10x Google9gmon system perf. phase error integrated histogram integrated 2x Google better 2-qubit gate error e2 by ~ 2-10x better.
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