Luke D Burkhart

Error-detected state transfer and entanglement in a superconducting quantum network

  1. Luke D Burkhart,
  2. James Teoh,
  3. Yaxing Zhang,
  4. Christopher J Axline,
  5. Luigi Frunzio,
  6. M.H. Devoret,
  7. Liang Jiang,
  8. S.M. Girvin,
  9. and R. J. Schoelkopf
Modular networks are a promising paradigm for increasingly complex quantum devices based on the ability to transfer qubits and generate entanglement between modules. These tasks require
a low-loss, high-speed intermodule link that enables extensible network connectivity. Satisfying these demands simultaneously remains an outstanding goal for long-range optical quantum networks as well as modular superconducting processors within a single cryostat. We demonstrate communication and entanglement in a superconducting network with a microwave-actuated beamsplitter transformation between two bosonic qubits, which are housed in separate modules and joined by a demountable coaxial bus resonator. We transfer a qubit in a multi-photon encoding and track photon loss events to improve the fidelity, making it as high as in a single-photon encoding. Furthermore, generating entanglement with two-photon interference and postselection against loss errors produces a Bell state with success probability 79% and fidelity 0.94, halving the error obtained with a single photon. These capabilities demonstrate several promising methods for faithful operations between modules, including novel possibilities for resource-efficient direct gates.
arxiv pdf

Schrodinger’s catapult: Launching multiphoton quantum states from a microwave cavity memory

  1. Wolfgang Pfaff,
  2. Christopher J Axline,
  3. Luke D Burkhart,
  4. Uri Vool,
  5. Philip Reinhold,
  6. Luigi Frunzio,
  7. Liang Jiang,
  8. Michel H. Devoret,
  9. and Robert J. Schoelkopf
Encoding quantum states in complex multiphoton fields can overcome loss during signal transmission in a quantum network. Transmitting quantum information encoded in this way requires
that locally stored states can be converted to propagating fields. Here we experimentally show the controlled conversion of multiphoton quantum states, like „Schr\“odinger cat“ states, from a microwave cavity quantum memory into propagating modes. By parametric conversion using the nonlinearity of a single Josephson junction, we can release the cavity state in ~500 ns, about 3 orders of magnitude faster than its intrinsic lifetime. This `catapult‘ faithfully converts arbitrary cavity fields to traveling signals with an estimated efficiency of > 90%, enabling on-demand generation of complex itinerant quantum states. Importantly, the release process can be controlled precisely on fast time scales, allowing us to generate entanglement between the cavity and the traveling mode by partial conversion. Our system can serve as the backbone of a microwave quantum network, paving the way towards error-correctable distribution of quantum information and the transfer of highly non-classical states to hybrid quantum systems.
arxiv pdf