D.N. Jamieson

Strong coupling of a superconducting flux qubit to single bismuth donors

  1. T. Chang,
  2. I. Holzman,
  3. S. Q. Lim,
  4. D. Holmes,
  5. B.C. Johnson,
  6. D.N. Jamieson,
  7. and M. Stern
The realization of a quantum computer represents a tremendous scientific and technological challenge due to the extreme fragility of quantum information. The physical support of information,
namely the quantum bit or qubit, must at the same time be strongly coupled to other qubits by gates to compute information, and well decoupled from its environment to keep its quantum behavior. An interesting physical system for realizing such qubits are magnetic impurities in semiconductors, such as bismuth donors in silicon. Indeed, spins associated to bismuth donors can reach an extremely long coherence time — of the order of seconds. Yet it is extremely difficult to establish and control efficient gates between these spins. Here we demonstrate a protocol where single bismuth donors can coherently transfer their quantum information to a superconducting flux qubit, which acts as a mediator or quantum bus. This superconducting device allows to connect distant spins on-demand with little impact on their coherent behavior.
arxiv pdf

Reproducibility and control of superconducting flux qubits

  1. T. Chang,
  2. I. Holzman,
  3. T. Cohen,
  4. B.C. Johnson,
  5. D.N. Jamieson,
  6. and M. Stern
Superconducting flux qubits are promising candidates for the physical realization of a scalable quantum processor. Indeed, these circuits may have both a small decoherence rate and
a large anharmonicity. These properties enable the application of fast quantum gates with high fidelity and reduce scaling limitations due to frequency crowding. The major difficulty of flux qubits‘ design consists of controlling precisely their transition energy – the so-called qubit gap – while keeping long and reproducible relaxation times. Solving this problem is challenging and requires extremely good control of e-beam lithography, oxidation parameters of the junctions and sample surface. Here we present measurements of a large batch of flux qubits and demonstrate a high level of reproducibility and control of qubit gaps, relaxation times and pure echo dephasing times. These results open the way for potential applications in the fields of quantum hybrid circuits and quantum computation.
arxiv pdf