Jonilyn Yoder

Deep Neural Network Discrimination of Multiplexed Superconducting Qubit States

  1. Benjamin Lienhard,
  2. Antti Vepsäläinen,
  3. Luke C.G. Govia,
  4. Cole R. Hoffer,
  5. Jack Y. Qiu,
  6. Diego Ristè,
  7. Matthew Ware,
  8. David Kim,
  9. Roni Winik,
  10. Alexander Melville,
  11. Bethany Niedzielski,
  12. Jonilyn Yoder,
  13. Guilhem J. Ribeill,
  14. Thomas A. Ohki,
  15. Hari K. Krovi,
  16. Terry P. Orlando,
  17. Simon Gustavsson,
  18. and William D. Oliver
Demonstrating the quantum computational advantage will require high-fidelity control and readout of multi-qubit systems. As system size increases, multiplexed qubit readout becomes
a practical necessity to limit the growth of resource overhead. Many contemporary qubit-state discriminators presume single-qubit operating conditions or require considerable computational effort, limiting their potential extensibility. Here, we present multi-qubit readout using neural networks as state discriminators. We compare our approach to contemporary methods employed on a quantum device with five superconducting qubits and frequency-multiplexed readout. We find that fully-connected feedforward neural networks increase the qubit-state-assignment fidelity for our system. Relative to contemporary discriminators, the assignment error rate is reduced by up to 25 % due to the compensation of system-dependent nonidealities such as readout crosstalk which is reduced by up to one order of magnitude. Our work demonstrates a potentially extensible building block for high-fidelity readout relevant to both near-term devices and future fault-tolerant systems.
arxiv pdf

Generating Spatially Entangled Itinerant Photons with Waveguide Quantum Electrodynamics

  1. Bharath Kannan,
  2. Daniel Campbell,
  3. Francisca Vasconcelos,
  4. Roni Winik,
  5. David Kim,
  6. Morten Kjaergaard,
  7. Philip Krantz,
  8. Alexander Melville,
  9. Bethany M. Niedzielski,
  10. Jonilyn Yoder,
  11. Terry P. Orlando,
  12. Simon Gustavsson,
  13. and William D. Oliver
Realizing a fully connected network of quantum processors requires the ability to distribute quantum entanglement. For distant processing nodes, this can be achieved by generating,
routing, and capturing spatially entangled itinerant photons. In this work, we demonstrate deterministic generation of such photons using superconducting transmon qubits that are directly coupled to a waveguide. In particular, we generate two-photon N00N states and show that the state and spatial entanglement of the emitted photons can be tuned via the qubit frequencies. Using quadrature amplitude detection, we reconstruct the moments and correlations of the photonic modes and demonstrate state preparation fidelities of 84%. Our results provide a path towards realizing quantum communication and teleportation protocols using non-classical, spatially entangled itinerant photons.
arxiv pdf

Two-qubit spectroscopy of spatiotemporally correlated quantum noise in superconducting qubits

  1. Uwe von Lüpke,
  2. Félix Beaudoin,
  3. Leigh M. Norris,
  4. Youngkyu Sung,
  5. Roni Winik,
  6. Jack Y. Qiu,
  7. Morten Kjaergaard,
  8. David Kim,
  9. Jonilyn Yoder,
  10. Simon Gustavsson,
  11. Lorenza Viola,
  12. and William D. Oliver
Noise that exhibits significant temporal and spatial correlations across multiple qubits can be especially harmful to both fault-tolerant quantum computation and quantum-enhanced metrology.
However, a complete spectral characterization of the noise environment of even a two-qubit system has not been reported thus far. We propose and experimentally validate a protocol for two-qubit dephasing noise spectroscopy based on continuous control modulation. By combining ideas from spin-locking relaxometry with a statistically motivated robust estimation approach, our protocol allows for the simultaneous reconstruction of all the single-qubit and two-qubit cross-correlation spectra, including access to their distinctive non-classical features. Only single-qubit control manipulations and state-tomography measurements are employed, with no need for entangled-state preparation or readout of two-qubit observables. While our experimental validation uses two superconducting qubits coupled to a shared engineered noise source, our methodology is portable to a variety of dephasing-dominated qubit architectures. By pushing quantum noise spectroscopy beyond the single-qubit setting, our work paves the way to characterizing spatiotemporal correlations in both engineered and naturally occurring noise environments.
arxiv pdf