Y. Y. Gao

Deterministic teleportation of a quantum gate between two logical qubits

  1. K.S. Chou,
  2. J. Z. Blumoff,
  3. C.S. Wang,
  4. P.C. Reinhold,
  5. C. J. Axline,
  6. Y. Y. Gao,
  7. L. Frunzio,
  8. M.H. Devoret,
  9. Liang Jiang,
  10. and R. J. Schoelkopf
A quantum computer has the potential to effciently solve problems that are intractable for classical computers. Constructing a large-scale quantum processor, however, is challenging
due to errors and noise inherent in real-world quantum systems. One approach to this challenge is to utilize modularity–a pervasive strategy found throughout nature and engineering–to build complex systems robustly. Such an approach manages complexity and uncertainty by assembling small, specialized components into a larger architecture. These considerations motivate the development of a quantum modular architecture, where separate quantum systems are combined via communication channels into a quantum network. In this architecture, an essential tool for universal quantum computation is the teleportation of an entangling quantum gate, a technique originally proposed in 1999 which, until now, has not been realized deterministically. Here, we experimentally demonstrate a teleported controlled-NOT (CNOT) operation made deterministic by utilizing real-time adaptive control. Additionally, we take a crucial step towards implementing robust, error-correctable modules by enacting the gate between logical qubits, encoding quantum information redundantly in the states of superconducting cavities. Such teleported operations have significant implications for fault-tolerant quantum computation, and when realized within a network can have broad applications in quantum communication, metrology, and simulations. Our results illustrate a compelling approach for implementing multi-qubit operations on logical qubits within an error-protected quantum modular architecture.
arxiv pdf

Normal-metal quasiparticle traps for superconducting qubits

  1. R.-P. Riwar,
  2. A. Hosseinkhani,
  3. L. D. Burkhart,
  4. Y. Y. Gao,
  5. R. J. Schoelkopf,
  6. L. I. Glazman,
  7. and G. Catelani
The presence of quasiparticles in superconducting qubits emerges as an intrinsic constraint on their coherence. While it is difficult to prevent the generation of quasiparticles, keeping
them away from active elements of the qubit provides a viable way of improving the device performance. Here we develop theoretically and validate experimentally a model for the effect of a single small trap on the dynamics of the excess quasiparticles injected in a transmon-type qubit. The model allows one to evaluate the time it takes to evacuate the injected quasiparticles from the transmon as a function of trap parameters. With the increase of the trap size, this time decreases monotonically, saturating at the level determined by the quasiparticles diffusion constant and the qubit geometry. We determine the characteristic trap size needed for the relaxation time to approach that saturation value.
arxiv pdf

Suspending superconducting qubits by silicon micromachining

  1. Y. Chu,
  2. C. Axline,
  3. C. Wang,
  4. T. Brecht,
  5. Y. Y. Gao,
  6. L. Frunzio,
  7. and R. J. Schoelkopf
We present a method for relieving aluminum 3D transmon qubits from a silicon substrate using micromachining. Our technique is a high yield, one-step deep reactive ion etch that requires
no additional fabrication processes, and results in the suspension of the junction area and edges of the aluminum film. The drastic change in the device geometry affects both the dielectric and flux noise environment experienced by the qubit. In particular, the participation ratios of various dielectric interfaces are significantly modified, and suspended qubits exhibited longer T1’s than non-suspended ones. We also find that suspension increases the flux noise experienced by tunable SQUID-based qubits.
arxiv pdf