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Quantum Computing and Qiskit
- 1. Exploring Quantum Computing withQiskit July 15, 2020 Doug McClure Research Staff Member Manager of Quantum System Deployment IBM Quantum
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- 3. 3IBM Confidential –Internal Use OnlyJuly 2019 3 © 2017 IBM Corporation Performance Moore’s Law • Transistors get smaller and cheaper
- 4. 4IBM Confidential –Internal Use OnlyJuly 2019 4 © 2017 IBM Corporation Performance Moore’s Law • Transistors get smaller and cheaper • Underlying model of computation still the same ENIAC (1945) Galaxy Z Flip (2020) =
- 5. 5IBM Confidential –Internal Use OnlyJuly 2019 5 © 2017 IBM Corporation Performance Beyond Moore’s Law • Quantum computing is an entirely new model of computation, NOT simply an extension of Moore’s law ENIAC (1945) = Galaxy Z Flip (2020) = IBM Quantum 20-qubit system (2018)
- 6. The road to quantum advantage 2016~2020s1960s 2050+ Quantum Science Quantum Ready Quantum Advantage Created the fundamental theoretical and physical building blocks of quantum computing. Engage the world and prepare for the quantum computing era. Beneficial to use a quantum computer to solve real- world problems. IBM Quantum Experience Launched (May 2016) IBM Quantum Network Launched (Dec 2017) Qiskit v0.1 released (Mar 2017)
- 7. Quantum mechanics: a two-sidedcoin Superposition Entanglement Uncertainty Decoherence
- 8. Computing with quantummechanics: features Superposition: a system’s state can be any linear combination of classical states …until it is measured, at which point it collapses to one of the classical states Example: Schrodinger’s Cat Entanglement: particles in superposition can develop correlations such that measuring just one affects them all Example: EPR Paradox (Einstein: “spooky action at a distance”) Quantum wavefunction Normalization “Classical” states Linear combination
- 9. Computing with quantummechanics: challenges Time QubitState 0 1 Decoherence: a system is gradually measured by residual interaction with its environment, killing quantum behavior Consequence: quantum effects observed only in well-isolated systems (so not cats… yet) Uncertainty principle: measuring one variable (e.g. position) disturbs its conjugate (e.g. momentum) Consequence: complete knowledge of an arbitrary quantum state is impossible. → “No-Cloning Theorem”
- 10. Classical bits: Quantum bits(“qubits”) What should a quantum bit look like? Physical systems: capacitor charge, transistor state, magnetic polarization, presence or absence of a punched hole, etc. Logical states: 0 and 1 Physical systems: spin of an electron, state of an atom, superconducting circuits Logical states: |0>, |1>, superpositions thereof. Represented on the Bloch sphere
- 11. Physical qubit systems Topological systems? Atomicsystems Electron spins Image: http://vandersypenlab.tudelft.nl/ Image: http://www.quantumoptics.at/ Image: http://topocondmat.org/ w2_majorana/braiding.html Majorana fermions Superconducting circuits • Straightforward wafer-scale fabrication with established materials and processes • Accurate device design with standard software • Scalable architecture with circuit QED paradigm • Control and readout using readily available components Photons Image: PSIQuantum
- 12. Superconducting Microwave Resonators: ▪ read-outof qubit states ▪ multi-qubit quantum bus ▪ noise filter Superconducting Transmon Qubits: Superconducting quantum processor building blocks 100 nm X 100 nm ▪ Josephson Junction acts as a non-linear inductor, allowing isolation of lowest two allowed energy levels Phys. Rev. A 76, 04319 (2007)
- 13. Anatomy of aquantum chip 1 mm Qubits: Single-junction transmon Frequency ~ 5 GHz Anharmonicity ~ 0.3 GHz Resonators: Co-planar waveguide Frequency ~ 6 – 7 GHz Roles: 1. Individual qubit readout 2. Qubit coupling (“bus”) Ground plane Periodic holes prevent stray magnetic field from hurting superconductor performance Corcoles et al., Nat. Commun. 6, 6979 (2015)
- 14. Controlling individual superconductingqubits • Typically | ۧ𝟎 and | ۧ𝟏 differ in energy by E01 ~ 20 meV • We drive this transition with a microwave pulse at frequency E01/h ~ 5 GHz • While pulse is on, qubit undergoes Rabi oscillations between | ۧ𝟎 and | ۧ𝟏 • Applying a pulse for just the right time and amplitude (a “pi pulse”) flips the qubit X Y Z | ۧ𝟎 | ۧ𝟏 | ۧ+ | ۧ− | ۧ| ۧ Pulse length Probabilityof measuring|ۧ𝟎 100% 0% “pi pulse” = NOT gate
- 15. Generating entanglement Various approachesdemonstrated: – Fast frequency tuning with flux bias – Tunable couplers – All-microwave control IBM Quantum systems use CNOT implemented using cross-resonance technique (all-microwave) – Bus resonator provides static coupling between neighboring qubits – Drive control at target’s frequency → target oscillates at rate dependent on state of control – Adjust amplitude/time of pulse to get CNOT – Error rates around 1% in multi-qubit devices Initial State Final State Control Target Control Target | ۧ𝟎 | ۧ𝟎 | ۧ𝟎 | ۧ𝟎 | ۧ𝟏 | ۧ𝟎 | ۧ𝟏 | ۧ𝟏 a | ۧ𝟎 + b | ۧ𝟏 | ۧ𝟎 a | ۧ𝟎𝟎 + b | ۧ𝟏𝟏 CNOT Gate Operation entanglement! superposition →
- 16. Superconducting qubit controland readout electronics • RF signal source • Produces a continuous sine wave at a requested frequency/power • Arbitrary waveform generator • Generates and outputs a programmed pulse envelope • Mixer • Multiplies a sine wave by an envelope to produce an RF pulse • Down-converts readout signal to MHz range to facilitate digitization • Digitizer • Captures down-converted readout signal for analysis RF Source: @ f01 AWG: Ch1 Ch2 I Q to qubit I/Q Mixer Qubit control: RF Source 1: @ fr Digitizer: @ D to readout resonator Qubit readout: RF Source 2: @ fr + D readout signal
- 17. Superconducting qubit environmentand signal flow • Cryo temperatures required ▪ Qubits sit at base of dilution refrigerator • Control and readout performed by sending pulses over coaxial cables • Input lines use attenuation to reduce incoming noise • Output lines use cryogenic amplification and isolation
- 18. IBM Quantum Experience LaunchedMay 4, 2016 Free, cloud-based GUI and programmatic access to small quantum devices and simulators Detailed user guide with example algorithms > 200,000 users > 150 billion circuits run > 200 scientific papers
- 19. © 2017 IBMCorporation19 Quantum computing through the cloud Classical computer API server Control computer Control instruments Quantum computer 1. User submits “circuits” (sets of instructions) via API 2. Control computer directs instruments to send pulses to quantum chip 3. Readout signals are analyzed to determine qubit states at end of each circuit 4. Typically repeat many times to average away fluctuations 5. Results sent to user
- 20. Writing quantum circuits:the “quantum score” arxiv.org/pdf/1905.02666.pdf • “Textbook” way of showing quantum circuits • Conducive to user-friendly drag-and-drop interface • Useful for beginners studying simple circuits • Becomes unmanageable for large/complex circuits
- 21. Quantum programming desires •Build and run circuits • Study and mitigate errors • Simulate device behavior • Solve real-world problems
- 22. The elements ofQiskit • Build and run circuits • Study and mitigate errors • Simulate device behavior • Solve real-world problems Terra Aqua Aer Ignis Open Source (Apache 2.0) Written in Python 3 Modular and extendible qiskit.org
- 23. © 2017 IBMCorporation23 Basic workflow (Qiskit Terra) ▪Define → build → compile → run → retrieve Compile and run Get resultsDefine quantum circuits State Counts 00000 513 00011 487 00000 00011 0.5 0.0 Probability Outcome
- 24. Designing algorithms fortoday’s quantum computers • Quantum processors are noisy → long circuits won’t work! ▪ Design algorithms to use many small circuits rather than a single big one • Example: “hybrid” quantum-classical optimization ▪ Quantum processor calculates objective function for classical optimizer ▪ Applicable to many problems including quantum chemistry (below) Prepare a trial state 𝝍 𝜽 and compute its energy 𝑬(𝜽) Use classical optimizer to guess a better value of 𝜽
- 25. Black dots: VQEresults Density plots: numerical simulations (classical) Dashed lines: exact calculations More recently: improved accuracy using error mitigation technique Prepare a trial state 𝝍 𝜽 and compute its energy 𝑬(𝜽) Use classical optimizer to guess a better value of 𝜽 Quantum Chemistry with the Variational Quantum Eigensolver (VQE)
- 26. Tour of IQXPlatform arxiv.org/pdf/1905.02666.pdf quantum-computing.ibm.com
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- 31. Circuit composer: quantumscore GUI arxiv.org/pdf/1905.02666.pdf
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- 33. Jupyter notebook environment arxiv.org/pdf/1905.02666.pdf Starta new notebook from scratch – or import one easy access to notebooks in qiskit-iqx-tutorials
- 34. Hands-On Exercise: creating superpositionand entanglement arxiv.org/pdf/1905.02666.pdf quantum-computing.ibm.com https://github.com/dtmcclure/exploring-qc-with-qiskit Step-by-step instructions at
- 35. 35 © 2017IBM Corporation Join the global Qiskit community ▪Diverse developer and user community ▪Slack workspace for questions and discussions ▪Online and in-person events (contests, hackathons, camps)
- 36. Learn more! Discover moreabout IBM’s quantum computing initiative ibm.com/IBMQ Explore the IBM Quantum Experience and start using real machines today (don’t miss the embedded tutorial at https://quantum- computing.ibm.com/docs/guide) ibm.co/iqx Learn the basics of programming quantum computers with Qiskit (I particularly recommend the Coding with Qiskit video series and the Qiskit Textbook) qiskit.org