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1. Quantum information phases in space-time: measurement-induced entanglement and teleportation on a noisy quantum processor

Author

Jesse Hoke, Matteo Ippoliti, Dmitry Abanin, Rajeev Acharya, Markus Ansmann, Frank Arute, Kunal Arya, Abraham Asfaw, Juan Atalaya, Ryan Babbush, Joseph Bardin, Andreas Bengtsson, Gina Bortoli, Alexandre Bourassa, Jenna Bovaird, Leon Brill, Michael Broughton, Bob Buckley, David Buell, Tim Burger, Brian Burkett, Nicholas Bushnell, Zijun Chen, Ben Chiaro, Desmond Chik, Charina Chou, Josh Cogan, Roberto Collins, Paul Conner, William Courtney, Alexander Crook, Ben Curtin, Alejandro Grajales Dau, Dripto Debroy, Alexander Del Toro Barba, Sean Demura, Augustin Di Paolo, Ilya Drozdov, Andrew Dunsworth, Daniel Eppens, Catherine Erickson, Lara Faoro, Edward Farhi, Reza Fatemi, Vinicius Ferreira, Leslie Flores Burgos, Ebrahim Forati, Austin Fowler, Brooks Foxen, William Giang, Craig Gidney, Dar Gilboa, Marissa Giustina, Raja Gosula, Jonathan Gross, Steve Habegger, Michael Hamilton, Monica Hansen, Matthew Harrigan, Sean Harrington, Paula Heu, Markus Hoffmann, Sabrina Hong, Trent Huang, Ashley Huff, William Huggins, Sergei Isakov, Justin Iveland, E. Jeffrey, Cody Jones, Pavol Juhas, Dvir Kafri, Kostyantyn Kechedzhi, Tanuj Khattar, Mostafa Khezri, Marika Kieferova, Seon Kim, Alexei Kitaev, Paul Klimov, Andrey Klots, Alexander Korotkov, Fedor Kostritsa, John Mark Kreikebaum, David Landhuis, Pavel Laptev, Kim-Ming Lau, Lily Laws, Joonho Lee, Kenny Lee, Yuri Lensky, Brian Lester, Alexander Lill, Wayne Liu, Aditya Locharla, Fionn Malone, Orion Martin, Jarrod McClean, Matt McEwen, Kevin Miao, Amanda Mieszala, Shirin Montazeri, Alexis Morvan, Ramis Movassagh, Wojciech Mruczkiewicz, Matthew Neeley, Charles Neill, Ani Nersisyan, Michael Newman, Jiun How Ng, Anthony Nguyen, Murray Nguyen, Murphy Niu, Thomas O'Brien, Seun Omonije, Alex Opremcak, Andre Petukhov, Rebecca Potter, Leonid Pryadko, Chris Quintana, Charles Rocque, Nicholas Rubin, Negar Saei, Daniel Sank, Kannan Sankaragomathi, Kevin Satzinger, Henry Schurkus, Christopher Schuster, Michael Shearn, Aaron Shorter, Noah Shutty, Shvarts Vladimir, Jindra Skruzny, W. Smith, Rolando Somma, George Sterling, Doug Strain, Marco Szalay, Alfredo Torres, Guifre Vidal, Benjamin Villalonga, Catherine Vollgraff Heidweiller, Theodore White, Bryan Woo, Cheng Xing, Z. Jamie Yao, Ping Yeh, Juhwan Yoo, Grayson Young, Adam Zalcman, Yaxing Zhang, Ningfeng Zhu, Nicholas Zobrist, Hartmut Neven, Dave Bacon, Sergio Boixo, Jeremy Hilton, Erik Lucero, Anthony Megrant, Julian Kelly, Yu Chen, Vadim Smelyanskiy, Xiao Mi, Vedika Khemani, and Pedram Roushan

Abstract

Measurement has a special role in quantum theory1: by collapsing the wavefunction it can enable phenomena such as teleportation2 and thereby alter the "arrow of time" that constrains unitary evolution. When integrated in many-body dynamics, measurements can lead to emergent patterns of quantum information in space-time3-10 that go beyond established paradigms for characterizing phases, either in or out of equilibrium11-13. On present-day NISQ processors14, the experimental realization of this physics is challenging due to noise, hardware limitations, and the stochastic nature of quantum measurement. Here we address each of these experimental challenges and investigate measurement-induced quantum information phases on up to 70 superconducting qubits. By leveraging the interchangeability of space and time, we use a duality mapping9,15-17 to avoid mid-circuit measurement and access different manifestations of the underlying phases—from entanglement scaling3,4 to measurement-induced teleportation18—in a unified way. We obtain finite-size signatures of a phase transition with a decoding protocol that correlates the experimental measurement record with classical simulation data. The phases display sharply different sensitivity to noise, which we exploit to turn an inherent hardware limitation into a useful diagnostic. Our work demonstrates an approach to realize measurement-induced physics at scales that are at the limits of current NISQ processors.

Published
2023

2. Resolving catastrophic error bursts from cosmic rays in large arrays of superconducting qubits

Author

Matt McEwen, Lara Faoro, Kunal Arya, Andrew Dunsworth, Trent Huang, Seon Kim, Brian Burkett, Austin Fowler, Frank Arute, Joseph C. Bardin, Andreas Bengtsson, Alexander Bilmes, Bob B. Buckley, Nicholas Bushnell, Zijun Chen, Roberto Collins, Sean Demura, Alan R. Derk, Catherine Erickson, Marissa Giustina, Sean D. Harrington, Sabrina Hong, Evan Jeffrey, Julian Kelly, Paul V. Klimov, Fedor Kostritsa, Pavel Laptev, Aditya Locharla, Xiao Mi, Kevin C. Miao, Shirin Montazeri, Josh Mutus, Ofer Naaman, Matthew Neeley, Charles Neill, Alex Opremcak, Chris Quintana, Nicholas Redd, Pedram Roushan, Daniel Sank, Kevin J. Satzinger, Vladimir Shvarts, Theodore White, Z. Jamie Yao, Ping Yeh, Juhwan Yoo, Yu Chen, Vadim Smelyanskiy, John M. Martinis, Hartmut Neven, Anthony Megrant, Lev Ioffe, Rami Barends, Laboratoire de Physique Théorique et Hautes Energies (LPTHE), Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), HEP, INSPIRE, and Faoro, Lara

Subjects
Quantum Physics, [SPI] Engineering Sciences [physics], [PHYS.PHYS.PHYS-GEN-PH] Physics [physics]/Physics [physics]/General Physics [physics.gen-ph], FOS: Physical sciences, General Physics and Astronomy, 02 engineering and technology, 021001 nanoscience & nanotechnology, 01 natural sciences, [PHYS.PHYS.PHYS-GEN-PH]Physics [physics]/Physics [physics]/General Physics [physics.gen-ph], [SPI]Engineering Sciences [physics], 0103 physical sciences, Quantum Physics (quant-ph), 010306 general physics, 0210 nano-technology
Abstract

Scalable quantum computing can become a reality with error correction, provided coherent qubits can be constructed in large arrays. The key premise is that physical errors can remain both small and sufficiently uncorrelated as devices scale, so that logical error rates can be exponentially suppressed. However, energetic impacts from cosmic rays and latent radioactivity violate both of these assumptions. An impinging particle ionizes the substrate, radiating high energy phonons that induce a burst of quasiparticles, destroying qubit coherence throughout the device. High-energy radiation has been identified as a source of error in pilot superconducting quantum devices, but lacking a measurement technique able to resolve a single event in detail, the effect on large scale algorithms and error correction in particular remains an open question. Elucidating the physics involved requires operating large numbers of qubits at the same rapid timescales as in error correction, exposing the event's evolution in time and spread in space. Here, we directly observe high-energy rays impacting a large-scale quantum processor. We introduce a rapid space and time-multiplexed measurement method and identify large bursts of quasiparticles that simultaneously and severely limit the energy coherence of all qubits, causing chip-wide failure. We track the events from their initial localised impact to high error rates across the chip. Our results provide direct insights into the scale and dynamics of these damaging error bursts in large-scale devices, and highlight the necessity of mitigation to enable quantum computing to scale.

Published
2021

3. Time-crystalline eigenstate order on a quantum processor

Author

Julian Kelly, Alexander Bilmes, Vedika Khemani, Seon Kim, Alexei Kitaev, Murphy Yuezhen Niu, J. Hilton, Orion Martin, Craig Gidney, Bob B. Buckley, Thomas E. O'Brien, Jarrod R. McClean, Alexander N. Korotkov, Pavel Laptev, Tanuj Khattar, Sabrina Hong, Daniel Eppens, Alan Ho, Aditya Locharla, Ofer Naaman, Ping Yeh, Juan Atalaya, Sean D. Harrington, Frank Arute, Roberto Collins, Joao Marcos Vensi Basso, Doug Strain, Matthew P. Harrigan, Zhang Jiang, Joonho Lee, Ami Greene, Alan R. Derk, Roderich Moessner, Bálint Pató, William J. Huggins, Trevor McCourt, Ashley Huff, Joseph C. Bardin, Andre Petukhov, Fedor Kostritsa, Michael Newman, Cody Jones, Sean Demura, Shivaji Lal Sondhi, B. Burkett, Sergio Boixo, Jonathan H. Gross, David A. Buell, Kevin J. Satzinger, Michael Broughton, Daniel Sank, Masoud Mohseni, Lev Ioffe, Yuan Su, Shirin Montazeri, Xiao Mi, Eric Ostby, Marissa Giustina, David Landhuis, Z. Jamie Yao, Kenny Lee, Kunal Arya, Pedram Roushan, Hartmut Neven, Sergei V. Isakov, Andrew Dunsworth, Zijun Chen, Matteo Ippoliti, Matthew Neeley, Nicholas C. Rubin, Austin G. Fowler, Anthony Megrant, Marco Szalay, Trent Huang, Evan Jeffrey, Leon Brill, Justin Iveland, Paul V. Klimov, Matthew D. Trevithick, William Courtney, Nicholas Bushnell, Theodore White, Alexandre Bourassa, E. Lucero, Edward Farhi, Vladimir Shvarts, Dripto M. Debroy, Benjamin Villalonga, Wojciech Mruczkiewicz, Chris Quintana, Juhwan Yoo, Benjamin Chiaro, Dvir Kafri, Brooks Foxen, Vadim Smelyanskiy, Ryan Babbush, Kostyantyn Kechedzhi, Charles Neill, Yu Chen, Andreas Bengtsson, Matt McEwen, A. Opremcak, Kevin C. Miao, Adam Zalcman, and Catherine Erickson

Subjects
Thermal equilibrium, Physics, Phase transition, Multidisciplinary, Quantum decoherence, Quantum information, Quantum simulator, Article, Phase Transition, Cold Temperature, Phase transitions and critical phenomena, Qubit, Thermodynamics, Statistical physics, Quantum simulation, Quantum, Quantum computer
Abstract

Quantum many-body systems display rich phase structure in their low-temperature equilibrium states1. However, much of nature is not in thermal equilibrium. Remarkably, it was recently predicted that out-of-equilibrium systems can exhibit novel dynamical phases2–8 that may otherwise be forbidden by equilibrium thermodynamics, a paradigmatic example being the discrete time crystal (DTC)7,9–15. Concretely, dynamical phases can be defined in periodically driven many-body-localized (MBL) systems via the concept of eigenstate order7,16,17. In eigenstate-ordered MBL phases, the entire many-body spectrum exhibits quantum correlations and long-range order, with characteristic signatures in late-time dynamics from all initial states. It is, however, challenging to experimentally distinguish such stable phases from transient phenomena, or from regimes in which the dynamics of a few select states can mask typical behaviour. Here we implement tunable controlled-phase (CPHASE) gates on an array of superconducting qubits to experimentally observe an MBL-DTC and demonstrate its characteristic spatiotemporal response for generic initial states7,9,10. Our work employs a time-reversal protocol to quantify the impact of external decoherence, and leverages quantum typicality to circumvent the exponential cost of densely sampling the eigenspectrum. Furthermore, we locate the phase transition out of the DTC with an experimental finite-size analysis. These results establish a scalable approach to studying non-equilibrium phases of matter on quantum processors., A study establishes a scalable approach to engineer and characterize a many-body-localized discrete time crystal phase on a superconducting quantum processor.

Published
2021

4. Readout of a quantum processor with high dynamic range Josephson parametric amplifiers

Author

Theodore White, Alex Opremcak, George Sterling, Alexander Korotkov, Daniel Sank, Rajeev Acharya, Markus Ansmann, Frank Arute, Kunal Arya, Joseph C. Bardin, Andreas Bengtsson, Alexandre Bourassa, Jenna Bovaird, Leon Brill, Bob B. Buckley, David A. Buell, Tim Burger, Brian Burkett, Nicholas Bushnell, Zijun Chen, Ben Chiaro, Josh Cogan, Roberto Collins, Alexander L. Crook, Ben Curtin, Sean Demura, Andrew Dunsworth, Catherine Erickson, Reza Fatemi, Leslie Flores Burgos, Ebrahim Forati, Brooks Foxen, William Giang, Marissa Giustina, Alejandro Grajales Dau, Michael C. Hamilton, Sean D. Harrington, Jeremy Hilton, Markus Hoffmann, Sabrina Hong, Trent Huang, Ashley Huff, Justin Iveland, Evan Jeffrey, Mária Kieferová, Seon Kim, Paul V. Klimov, Fedor Kostritsa, John Mark Kreikebaum, David Landhuis, Pavel Laptev, Lily Laws, Kenny Lee, Brian J. Lester, Alexander Lill, Wayne Liu, Aditya Locharla, Erik Lucero, Trevor McCourt, Matt McEwen, Xiao Mi, Kevin C. Miao, Shirin Montazeri, Alexis Morvan, Matthew Neeley, Charles Neill, Ani Nersisyan, Jiun How Ng, Anthony Nguyen, Murray Nguyen, Rebecca Potter, Chris Quintana, Pedram Roushan, Kannan Sankaragomathi, Kevin J. Satzinger, Christopher Schuster, Michael J. Shearn, Aaron Shorter, Vladimir Shvarts, Jindra Skruzny, W. Clarke Smith, Marco Szalay, Alfredo Torres, Bryan W. K. Woo, Z. Jamie Yao, Ping Yeh, Juhwan Yoo, Grayson Young, Ningfeng Zhu, Nicholas Zobrist, Yu Chen, Anthony Megrant, Julian Kelly, and Ofer Naaman

Subjects
Superconductivity (cond-mat.supr-con), Quantum Physics, Physics and Astronomy (miscellaneous), Condensed Matter - Superconductivity, FOS: Physical sciences, Applied Physics (physics.app-ph), Physics - Applied Physics, Quantum Physics (quant-ph)
Abstract

We demonstrate a high dynamic range Josephson parametric amplifier (JPA) in which the active nonlinear element is implemented using an array of rf-SQUIDs. The device is matched to the 50 $\Omega$ environment with a Klopfenstein-taper impedance transformer and achieves a bandwidth of 250-300 MHz, with input saturation powers up to -95 dBm at 20 dB gain. A 54-qubit Sycamore processor was used to benchmark these devices, providing a calibration for readout power, an estimate of amplifier added noise, and a platform for comparison against standard impedance matched parametric amplifiers with a single dc-SQUID. We find that the high power rf-SQUID array design has no adverse effect on system noise, readout fidelity, or qubit dephasing, and we estimate an upper bound on amplifier added noise at 1.6 times the quantum limit. Lastly, amplifiers with this design show no degradation in readout fidelity due to gain compression, which can occur in multi-tone multiplexed readout with traditional JPAs., Comment: 10 pages, 10 figures

Published
2022

5. Purification-based quantum error mitigation of pair-correlated electron simulations

Author

Thomas O'Brien, Gian-Luca Anselmetti, Fotios Gkritsis, Vincent Elfving, Stefano Polla, William Huggins, Oumarou Oumarou, Kostyantyn Kechedzhi, Dmitry Abanin, Rajeev Acharya, Igor Aleiner, Richard Allen, Trond Andersen, Kyle Anderson, Markus Ansmann, Frank Arute, Kunal Arya, Abraham Asfaw, Juan Atalaya, Dave Bacon, Joseph Bardin, Andreas Bengtsson, Sergio Boixo, Gina Bortoli, Alexandre Bourassa, Jenna Bovaird, Leon Brill, Michael Broughton, Bob Buckley, David Buell, Tim Burger, Brian Burkett, Nicholas Bushnell, Juan Campero, Yu Chen, Zijun Chen, Ben Chiaro, Desmond Chik, Josh Cogan, Roberto Collins, Paul Conner, William Courtney, Alexander Crook, Ben Curtin, Dripto Debroy, Alexander Del Toro Barba, Sean Demura, Ilya Drozdov, Andrew Dunsworth, Daniel Eppens, Catherine Erickson, Lara Faoro, Edward Farhi, Reza Fatemi, Vinicius Ferreira, Leslie Flores Burgos, Ebrahim Forati, Austin Fowler, Brooks Foxen, William Giang, Craig Gidney, Dar Gilboa, Marissa Giustina, Raja Gosula, Alejandro Grajales Dau, Jonathan Gross, Steve Habegger, Michael Hamilton, Monica Hansen, Matthew Harrigan, Sean Harrington, Paula Heu, Jeremy Hilton, Markus Hoffmann, Sabrina Hong, Trent Huang, Ashley Huff, L. B. Ioffe, Sergei Isakov, Justin Iveland, E. Jeffrey, Zhang Jiang, Cody Jones, Pavol Juhas, Dvir Kafri, Julian Kelly, Tanuj Khattar, Mostafa Khezri, Marika Kieferova, Seon Kim, Paul Klimov, Andrey Klots, Alexander Korotkov, Fedor Kostritsa, John Mark Kreikebaum, David Landhuis, Pavel Laptev, Kim-Ming Lau, Lily Laws, Joonho Lee, Kenny Lee, Brian Lester, Alexander Lill, Wayne Liu, William Livingston, Aditya Locharla, Erik Lucero, Fionn Malone, Salvatore Mandra, Orion Martin, Steven Martin, Jarrod McClean, Trevor McCourt, Matthew McEwen, Anthony Megrant, Xiao Mi, Kevin Miao, Amanda Mieszala, Masoud Mohseni, Shirin Montazeri, Alexis Morvan, Ramis Movassagh, Wojciech Mruczkiewicz, Ofer Naaman, Matthew Neeley, Charles Neill, Ani Nersisyan, Hartmut Neven, Michael Newman, Jiun How Ng, Anthony Nguyen, Murray Nguyen, Murphy Niu, Seun Omonije, Alex Opremcak, Andre Petukhov, Rebecca Potter, Leonid Pryadko, Chris Quintana, Charles Rocque, Pedram Roushan, Negar Saei, Daniel Sank, Kannan Sankaragomathi, Kevin Satzinger, Henry Schurkus, Michael Shearn, Aaron Shorter, Noah Shutty, Shvarts Vladimir, Jindra Skruzny, Vadim Smelyanskiy, W. Clarke Smith, Rolando Somma, George Sterling, Doug Strain, Marco Szalay, Douglas Thor, Alfredo Torres, Guifre Vidal, Benjamin Villalonga, Catherine Vollgraff Heidweiller, Theodore White, Bryan Woo, Cheng Xing, Z. Jamie Yao, Ping Yeh, Juhwan Yoo, Grayson Young, Adam Zalcman, Yaxing Zhang, Ningfeng Zhu, Nicholas Zobrist, Christian Gogolin, Ryan Babbush, and Nicholas Rubin

Subjects
Quantum Physics, FOS: Physical sciences, Quantum Physics (quant-ph)
Abstract

An important measure of the development of quantum computing platforms has been the simulation of increasingly complex physical systems. Prior to fault-tolerant quantum computing, robust error mitigation strategies are necessary to continue this growth. Here, we study physical simulation within the seniority-zero electron pairing subspace, which affords both a computational stepping stone to a fully correlated model, and an opportunity to validate recently introduced ``purification-based'' error-mitigation strategies. We compare the performance of error mitigation based on doubling quantum resources in time (echo verification) or in space (virtual distillation), on up to $20$ qubits of a superconducting qubit quantum processor. We observe a reduction of error by one to two orders of magnitude below less sophisticated techniques (e.g. post-selection); the gain from error mitigation is seen to increase with the system size. Employing these error mitigation strategies enables the implementation of the largest variational algorithm for a correlated chemistry system to-date. Extrapolating performance from these results allows us to estimate minimum requirements for a beyond-classical simulation of electronic structure. We find that, despite the impressive gains from purification-based error mitigation, significant hardware improvements will be required for classically intractable variational chemistry simulations., Comment: 10 pages, 13 page supplementary material, 12 figures. Experimental data available at https://doi.org/10.5281/zenodo.7225821

Published
2022
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6. Information scrambling in quantum circuits

Author

Roberto Collins, Trevor McCourt, Sabrina Hong, Brooks Foxen, Michael Broughton, Daniel Eppens, Alan Ho, Kevin J. Satzinger, Cody Jones, Edward Farhi, Lev Ioffe, William J. Huggins, Joao Marcos Vensi Basso, Doug Strain, Z. Jamie Yao, Alexandre Bourassa, Xiao Mi, Andrew Dunsworth, Bob B. Buckley, Marissa Giustina, David Landhuis, Vadim Smelyanskiy, Josh Mutus, Sean Demura, Daniel Sank, Craig Gidney, Kostyantyn Kechedzhi, Kunal Arya, Andre Petukhov, Juan Atalaya, Alan R. Derk, Pavel Laptev, Igor L. Aleiner, Alexei Kitaev, David A. Buell, A. Opremcak, Joseph C. Bardin, Murphy Yuezhen Niu, B. Burkett, Julian Kelly, Masoud Mohseni, Michael Newman, Sergei V. Isakov, Ryan Babbush, Eric Ostby, Nicholas C. Rubin, Rami Barends, Sean D. Harrington, Pedram Roushan, Frank Arute, Paul V. Klimov, Fedor Kostritsa, Hartmut Neven, Alexander N. Korotkov, Salvatore Mandrà, Sergio Boixo, Austin G. Fowler, Jeffrey S. Marshall, Zhang Jiang, Chris Quintana, Zijun Chen, Matthew Neeley, Benjamin Chiaro, Seon Kim, Dvir Kafri, Matthew P. Harrigan, Kevin C. Miao, Bálint Pató, J. Hilton, Orion Martin, Charles Neill, Yu Chen, Andreas Bengtsson, Thomas E. O'Brien, Jarrod R. McClean, Ofer Naaman, Ping Yeh, Nicholas Redd, Matt McEwen, Evan Jeffrey, Trent Huang, Shirin Montazeri, Anthony Megrant, Marco Szalay, William Courtney, Wojciech Mruczkiewicz, Nicholas Bushnell, Theodore White, Jonathan A. Gross, Benjamin Villalonga, E. Lucero, Vladimir Shvarts, Catherine Erickson, Adam Zalcman, and Matthew D. Trevithick

Subjects
2019-20 coronavirus outbreak, Multidisciplinary, Computer science, Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), Degrees of freedom, Process (computing), TheoryofComputation_GENERAL, Statistical physics, Quantum information, Quantum, Scrambling, Electronic circuit
Abstract

Interactions in quantum systems can spread initially localized quantum information into the exponentially many degrees of freedom of the entire system. Understanding this process, known as quantum scrambling, is key to resolving several open questions in physics. Here, by measuring the time-dependent evolution and fluctuation of out-of-time-order correlators, we experimentally investigate the dynamics of quantum scrambling on a 53-qubit quantum processor. We engineer quantum circuits that distinguish operator spreading and operator entanglement and experimentally observe their respective signatures. We show that whereas operator spreading is captured by an efficient classical model, operator entanglement in idealized circuits requires exponentially scaled computational resources to simulate. These results open the path to studying complex and practically relevant physical observables with near-term quantum processors.

Published
2021

7. Exponential suppression of bit or phase errors with cyclic error correction

Author

Andre Petukhov, Erik Lucero, Ofer Naaman, Ping Yeh, Wojciech Mruczkiewicz, David A. Buell, Alexander N. Korotkov, Masoud Mohseni, Harald Putterman, Charles Neill, Catherine Erickson, Andrew Dunsworth, Sean D. Harrington, Frank Arute, Doug Strain, Edward Farhi, Yu Chen, Andreas Bengtsson, Jonathan A. Gross, Rami Barends, Pedram Roushan, Ami Greene, Hartmut Neven, Paul V. Klimov, William Courtney, Daniel Sank, Sergio Boixo, Evan Jeffrey, Alan R. Derk, Nicholas Redd, Alexei Kitaev, Matt McEwen, Nicholas Bushnell, Theodore White, Murphy Yuezhen Niu, Roberto Collins, Austin G. Fowler, Josh Mutus, Alexandre Bourassa, Zhang Jiang, Seon Jeong Kim, Juan Atalaya, Craig Gidney, B. Burkett, Z. Jamie Yao, William J. Huggins, Anthony Megrant, Kunal Arya, Brooks Foxen, Fedor Kostritsa, Jeremy P. Hilton, Joseph C. Bardin, Vladimir Shvarts, Bob B. Buckley, Marco Szalay, Chris Quintana, Benjamin Chiaro, Zijun Chen, Matthew Neeley, Vadim Smelyanskiy, Dvir Kafri, Kostyantyn Kechedzhi, Bálint Pató, A. Opremcak, Juhwan Yoo, Pavel Laptev, Adam Zalcman, Sean Demura, Alexandru Paler, Xiao Mi, Marissa Giustina, David Landhuis, Igor L. Aleiner, Kevin C. Miao, Ryan Babbush, Benjamin Villalonga, Trevor McCourt, Trent Huang, Sergei V. Isakov, Eric Ostby, Nicholas C. Rubin, Cody Jones, Michael Broughton, Lev Ioffe, Kevin J. Satzinger, Matthew P. Harrigan, Sabrina Hong, Daniel Eppens, Alan Ho, Shirin Montazeri, Julian Kelly, Michael Newman, Orion Martin, Thomas E. O'Brien, Jarrod R. McClean, and Matthew D. Trevithick

Subjects
Physics, Multidisciplinary, Quantum information, Phase (waves), 01 natural sciences, Article, 010305 fluids & plasmas, Exponential function, Bit (horse), 0103 physical sciences, 010306 general physics, Error detection and correction, Algorithm, Qubits
Abstract

Realizing the potential of quantum computing requires sufficiently low logical error rates1. Many applications call for error rates as low as 10−15 (refs. 2–9), but state-of-the-art quantum platforms typically have physical error rates near 10−3 (refs. 10–14). Quantum error correction15–17 promises to bridge this divide by distributing quantum logical information across many physical qubits in such a way that errors can be detected and corrected. Errors on the encoded logical qubit state can be exponentially suppressed as the number of physical qubits grows, provided that the physical error rates are below a certain threshold and stable over the course of a computation. Here we implement one-dimensional repetition codes embedded in a two-dimensional grid of superconducting qubits that demonstrate exponential suppression of bit-flip or phase-flip errors, reducing logical error per round more than 100-fold when increasing the number of qubits from 5 to 21. Crucially, this error suppression is stable over 50 rounds of error correction. We also introduce a method for analysing error correlations with high precision, allowing us to characterize error locality while performing quantum error correction. Finally, we perform error detection with a small logical qubit using the 2D surface code on the same device18,19 and show that the results from both one- and two-dimensional codes agree with numerical simulations that use a simple depolarizing error model. These experimental demonstrations provide a foundation for building a scalable fault-tolerant quantum computer with superconducting qubits., Repetition codes running many cycles of quantum error correction achieve exponential suppression of errors with increasing numbers of qubits.

Published
2021

8. Quantum supremacy using a programmable superconducting processor

Author

Josh Mutus, Rami Barends, Pedram Roushan, Andre Petukhov, Erik Lucero, Roberto Collins, Hartmut Neven, Paul V. Klimov, Z. Jamie Yao, Austin G. Fowler, Julian Kelly, Xiao Mi, Ryan Babbush, Matthew P. Harrigan, Marissa Giustina, David Landhuis, Jarrod R. McClean, B. Burkett, Joseph C. Bardin, Michael J. Hartmann, Rupak Biswas, Amit Vainsencher, Steve Habegger, Daniel Sank, Eric Ostby, William Courtney, Alexander N. Korotkov, Alan Ho, Keith Guerin, Ofer Naaman, Ping Yeh, Frank Arute, Kevin Sung, Zhang Jiang, Mike Lindmark, Markus R. Hoffmann, Salvatore Mandrà, Matthew D. Trevithick, Fernando G. S. L. Brandão, Dave Bacon, Anthony Megrant, Trent Huang, Theodore White, Andrew Dunsworth, Ben Chiaro, Kristel Michielsen, Adam Zalcman, David A. Buell, Evan Jeffrey, Benjamin Villalonga, John M. Martinis, Kevin J. Satzinger, Eleanor Rieffel, John Platt, Masoud Mohseni, Sergei V. Isakov, R. Graff, Sergio Boixo, Nicholas C. Rubin, Fedor Kostritsa, Dmitry I. Lyakh, Murphy Yuezhen Niu, Sergey Knysh, Kunal Arya, Zijun Chen, Matthew Neeley, Travis S. Humble, Craig Gidney, Chris Quintana, Charles Neill, Yu Chen, Dvir Kafri, Matt McEwen, Brooks Foxen, Vadim Smelyanskiy, Kostyantyn Kechedzhi, and Edward Farhi

Subjects
Superconductivity, Multidisciplinary, Programming language, Computer science, Section (typography), 02 engineering and technology, 021001 nanoscience & nanotechnology, computer.software_genre, 01 natural sciences, law.invention, Consistency (statistics), law, 0103 physical sciences, CLARITY, ddc:500, 010306 general physics, 0210 nano-technology, computer, Quantum
Abstract

The promise of quantum computers is that certain computational tasks might be executed exponentially faster on a quantum processor than on a classical processor1. A fundamental challenge is to build a high-fidelity processor capable of running quantum algorithms in an exponentially large computational space. Here we report the use of a processor with programmable superconducting qubits to create quantum states on 53 qubits, corresponding to a computational state-space of dimension 2^53 (about 10^16). Measurements from repeated experiments sample the resulting probability distribution, which we verify using classical simulations. Our Sycamore processor takes about 200 seconds to sample one instance of a quantum circuit a million times—our benchmarks currently indicate that the equivalent task for a state-of-the-art classical supercomputer would take approximately 10,000 years. This dramatic increase in speed compared to all known classical algorithms is an experimental realization of quantum supremacy for this specific computational task, heralding a much-anticipated computing paradigm.

Published
2019

9. Quantum approximate optimization of non-planar graph problems on a planar superconducting processor

Author

Wojciech Mruczkiewicz, Harald Putterman, Amit Vainsencher, Sergei V. Isakov, Sergio Boixo, Nicholas C. Rubin, Paul V. Klimov, Trent Huang, Andrew Dunsworth, Ofer Naaman, Ping Yeh, B. Burkett, E. Lucero, Michael Broughton, Lev Ioffe, Edward Farhi, Florian Neukart, Frank Arute, Kevin J. Sung, Zijun Chen, Matthew Neeley, Roberto Collins, Bryan O'Gorman, Kevin J. Satzinger, Juan Atalaya, Josh Mutus, Sabrina Hong, Daniel Eppens, Alan Ho, Nicholas Bushnell, Bob B. Buckley, Craig Gidney, Theodore White, Daniel Sank, Chris Quintana, Brooks Foxen, Dvir Kafri, Seon Kim, Pavel Laptev, Joseph C. Bardin, Andre Petukhov, Andrea Skolik, Ben Chiaro, Michael Streif, Dave Bacon, Orion Martin, Sean Demura, David A. Buell, Julian Kelly, Masoud Mohseni, Rami Barends, Kunal Arya, Pedram Roushan, Vadim Smelyanskiy, Hartmut Neven, Thomas E. O'Brien, Evan Jeffrey, Jarrod R. McClean, John M. Martinis, Kostyantyn Kechedzhi, William Courtney, Alexander N. Korotkov, Austin G. Fowler, Martin Leib, Charles Neill, Yu Chen, Xiao Mi, Marissa Giustina, David Landhuis, Z. Jamie Yao, Matt McEwen, Anthony Megrant, Doug Strain, Adam Zalcman, Marco Szalay, R. Graff, Fedor Kostritsa, Zhang Jiang, Ryan Babbush, Leo Zhou, Steve Habegger, Murphy Yuezhen Niu, Cody Jones, Matthew P. Harrigan, Eric Ostby, and Mike Lindmark

Subjects
Physics, Quantum Physics, Optimization problem, FOS: Physical sciences, General Physics and Astronomy, 01 natural sciences, 010305 fluids & plasmas, Planar graph, Quantum technology, symbols.namesake, Qubit, 0103 physical sciences, Benchmark (computing), symbols, Combinatorial optimization, Quantum Physics (quant-ph), 010306 general physics, Algorithm, Quantum, Quantum computer
Abstract

We demonstrate the application of the Google Sycamore superconducting qubit quantum processor to combinatorial optimization problems with the quantum approximate optimization algorithm (QAOA). Like past QAOA experiments, we study performance for problems defined on the (planar) connectivity graph of our hardware; however, we also apply the QAOA to the Sherrington-Kirkpatrick model and MaxCut, both high dimensional graph problems for which the QAOA requires significant compilation. Experimental scans of the QAOA energy landscape show good agreement with theory across even the largest instances studied (23 qubits) and we are able to perform variational optimization successfully. For problems defined on our hardware graph we obtain an approximation ratio that is independent of problem size and observe, for the first time, that performance increases with circuit depth. For problems requiring compilation, performance decreases with problem size but still provides an advantage over random guessing for circuits involving several thousand gates. This behavior highlights the challenge of using near-term quantum computers to optimize problems on graphs differing from hardware connectivity. As these graphs are more representative of real world instances, our results advocate for more emphasis on such problems in the developing tradition of using the QAOA as a holistic, device-level benchmark of quantum processors., 19 pages, 15 figures

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