Manuel H. Muñoz-Arias

Deterministic generation of a 20-qubit two-dimensional photonic cluster state

  1. James O'Sullivan,
  2. Kevin Reuer,
  3. Aleksandr Grigorev,
  4. Xi Dai,
  5. Alonso Hernández-Antón,
  6. Manuel H. Muñoz-Arias,
  7. Christoph Hellings,
  8. Alexander Flasby,
  9. Dante Colao Zanuz,
  10. Jean-Claude Besse,
  11. Alexandre Blais,
  12. Daniel Malz,
  13. Christopher Eichler,
  14. and Andreas Wallraff
Multidimensional cluster states are a key resource for robust quantum communication, measurement-based quantum computing and quantum metrology. Here, we present a device capable of
emitting large-scale entangled microwave photonic states in a two dimensional ladder structure. The device consists of a pair of coupled superconducting transmon qubits which are each tuneably coupled to a common output waveguide. This architecture permits entanglement between each transmon and a deterministically emitted photonic qubit. By interleaving two-qubit gates with controlled photon emission, we generate 2 x n grids of time- and frequency-multiplexed cluster states of itinerant microwave photons. We measure a signature of localizable entanglement across up to 20 photonic qubits. We expect the device architecture to be capable of generating a wide range of other tensor network states such as tree graph states, repeater states or the ground state of the toric code, and to be readily scalable to generate larger and higher dimensional states.
arxiv pdf

Qubit readouts enabled by qubit cloaking

  1. Manuel H. Muñoz-Arias,
  2. Cristóbal Lledó,
  3. and Alexandre Blais
Time-dependent drives play a crucial role in quantum computing efforts with circuit quantum electrodynamics. They enable single-qubit control, entangling logical operations, as well
as qubit readout. However, their presence can lead to deleterious effects such as large ac-Stark shifts and unwanted qubit transitions ultimately reflected into reduced control or readout fidelities. Qubit cloaking was introduced in Lledó, Dassonneville, et al. [arXiv:2022.05758] to temporarily decouple the qubit from the coherent photon population of a driven cavity, allowing for the application of arbitrary displacements to the cavity field while avoiding the deleterious effects on the qubit. For qubit readout, cloaking permits to prearm the cavity with an, in principle, arbitrarily large number of photons, in anticipation to the qubit-state-dependent evolution of the cavity field, allowing for improved readout strategies. Here we take a closer look at two of them. First, arm-and-release readout, introduced together with qubit cloaking, where after arming the cavity the cloaking mechanism is released and the cavity field evolves under the application of a constant drive amplitude. Second, an arm-and-longitudinal readout scheme, where the cavity drive amplitude is slowly modulated after the release. We show that the two schemes complement each other, offering an improvement over the standard dispersive readout for any values of the dispersive interaction and cavity decay rate, as well as any target measurement integration time. Our results provide a recommendation for improving qubit readout without changes to the standard circuit QED architecture.
arxiv pdf