Joel I.J. Wang

Deterministic remote entanglement using a chiral quantum interconnect

  1. Aziza Almanakly,
  2. Beatriz Yankelevich,
  3. Max Hays,
  4. Bharath Kannan,
  5. Reouven Assouly,
  6. Alex Greene,
  7. Michael Gingras,
  8. Bethany M. Niedzielski,
  9. Hannah Stickler,
  10. Mollie E. Schwartz,
  11. Kyle Serniak,
  12. Joel I.J. Wang,
  13. Terry P. Orlando,
  14. Simon Gustavsson,
  15. Jeffrey A. Grover,
  16. and William D. Oliver
Quantum interconnects facilitate entanglement distribution between non-local computational nodes. For superconducting processors, microwave photons are a natural means to mediate this
distribution. However, many existing architectures limit node connectivity and directionality. In this work, we construct a chiral quantum interconnect between two nominally identical modules in separate microwave packages. We leverage quantum interference to emit and absorb microwave photons on demand and in a chosen direction between these modules. We optimize the protocol using model-free reinforcement learning to maximize absorption efficiency. By halting the emission process halfway through its duration, we generate remote entanglement between modules in the form of a four-qubit W state with 62.4 +/- 1.6% (leftward photon propagation) and 62.1 +/- 1.2% (rightward) fidelity, limited mainly by propagation loss. This quantum network architecture enables all-to-all connectivity between non-local processors for modular and extensible quantum computation.
arxiv pdf

Hexagonal Boron Nitride (hBN) as a Low-loss Dielectric for Superconducting Quantum Circuits and Qubits

  1. Joel I.J. Wang,
  2. Megan A. Yamoah,
  3. Qing Li,
  4. Amir Karamlou,
  5. Thao Dinh,
  6. Bharath Kannan,
  7. Jochen Braumüller,
  8. David Kim,
  9. Alexander J. Melville,
  10. Sarah E. Muschinske,
  11. Bethany M. Niedzielski,
  12. Kyle Serniak,
  13. Youngkyu Sung,
  14. Roni Winik,
  15. Jonilyn L. Yoder,
  16. Mollie Schwartz,
  17. Kenji Watanabe,
  18. Takashi Taniguchi,
  19. Terry P. Orlando,
  20. Simon Gustavsson,
  21. Pablo Jarillo-Herrero,
  22. and William D. Oliver
Dielectrics with low loss at microwave frequencies are imperative for high-coherence solid-state quantum computing platforms. We study the dielectric loss of hexagonal boron nitride
(hBN) thin films in the microwave regime by measuring the quality factor of parallel-plate capacitors (PPCs) made of NbSe2-hBN-NbSe2 heterostructures integrated into superconducting circuits. The extracted microwave loss tangent of hBN is bounded to be at most in the mid-10-6 range in the low temperature, single-photon regime. We integrate hBN PPCs with aluminum Josephson junctions to realize transmon qubits with coherence times reaching 25 μs, consistent with the hBN loss tangent inferred from resonator measurements. The hBN PPC reduces the qubit feature size by approximately two-orders of magnitude compared to conventional all-aluminum coplanar transmons. Our results establish hBN as a promising dielectric for building high-coherence quantum circuits with substantially reduced footprint and, with a high energy participation that helps to reduce unwanted qubit cross-talk.
arxiv pdf

A tunable coupling scheme for implementing high-fidelity two-qubit gates

  1. Fei Yan,
  2. Philip Krantz,
  3. Youngkyu Sung,
  4. Morten Kjaergaard,
  5. Dan Campbell,
  6. Joel I.J. Wang,
  7. Terry P. Orlando,
  8. Simon Gustavsson,
  9. and William D. Oliver
The prospect of computational hardware with quantum advantage relies critically on the quality of quantum gate operations. Imperfect two-qubit gates is a major bottleneck for achieving
scalable quantum information processors. Here, we propose a generalizable and extensible scheme for a two-qubit coupler switch that controls the qubit-qubit coupling by modulating the coupler frequency. Two-qubit gate operations can be implemented by operating the coupler in the dispersive regime, which is non-invasive to the qubit states. We investigate the performance of the scheme by simulating a universal two-qubit gate on a superconducting quantum circuit, and find that errors from known parasitic effects are strongly suppressed. The scheme is compatible with existing high-coherence hardware, thereby promising a higher gate fidelity with current technologies.
arxiv pdf