Matti Silveri

New class of quantum error-correcting codes for a bosonic mode

  1. Marios H. Michael,
  2. Matti Silveri,
  3. R. T. Brierley,
  4. Victor V. Albert,
  5. Juha Salmilehto,
  6. Liang Jiang,
  7. and S. M. Girvin
We construct a new class of quantum error-correcting codes for a bosonic mode which are advantageous for applications in quantum memories, communication, and scalable computation. These
`binomial quantum codes‘ are formed from a finite superposition of Fock states weighted with binomial coefficients. The binomial codes can exactly correct errors that are polynomial up to a specific degree in bosonic creation and annihilation operators, including amplitude damping and displacement noise as well as boson addition and dephasing errors. For realistic continuous-time dissipative evolution, the codes can perform approximate quantum error correction to any given order in the timestep between error detection measurements. We present an explicit approximate quantum error recovery operation based on projective measurements and unitary operations. The binomial codes are tailored for detecting boson loss and gain errors by means of measurements of the generalized number parity. We discuss optimization of the binomial codes and demonstrate that by relaxing the parity structure, codes with even lower unrecoverable error rates can be achieved. The binomial codes are related to existing two-mode bosonic codes but offer the advantage of requiring only a single bosonic mode to correct amplitude damping as well as the ability to correct other errors. Our codes are similar in spirit to `cat codes‘ based on superpositions of the coherent states, but offer several advantages such as smaller mean number, exact rather than approximate orthonormality of the code words, and an explicit unitary operation for repumping energy into the bosonic mode. The binomial quantum codes are realizable with current superconducting circuit technology and they should prove useful in other quantum technologies, including bosonic quantum memories, photonic quantum communication, and optical-to-microwave up- and down-conversion.
arxiv pdf

Theory of remote entanglement via quantum-limited phase-preserving amplification

  1. Matti Silveri,
  2. Evan Zalys-Geller,
  3. Michael Hatridge,
  4. Zaki Leghtas,
  5. Michel H. Devoret,
  6. and S. M. Girvin
We show that a quantum-limited phase-preserving amplifier can act as a which-path information eraser when followed by detection of both quadratures. This beam splitter with gain implements
a continuous joint measurement on the signal sources. As an application, we propose heralded remote entanglement generation between two qubits coupled dispersively to separate cavities. Dissimilar qubit-cavity pairs can be made indistinguishable by simple engineering of the cavity driving fields providing experimental flexibility and the prospect for scalability. Additionally, we find an analytic solution for the stochastic master equation, a quantum filter, yielding a thorough physical understanding of the nonlinear measurement process leading to an entangled state of the qubits.
arxiv pdf

Charge qubit driven via the Josephson nonlinearity

  1. Jani Tuorila,
  2. Matti Silveri,
  3. Mika Sillanpää,
  4. Erkki Thuneberg,
  5. Yuriy Makhlin,
  6. and Pertti Hakonen
We study the novel nonlinear phenomena that emerge in a charge qubit due to the interplay between a strong microwave flux drive and a periodic Josephson potential. We first analyze
the system in terms of the linear Landau-Zener-St\“uckelberg model, and show its inadequacy in a periodic system with several Landau-Zener crossings within a drive period. Experimentally, we probe the quasienergy levels of the driven qubit with an LC-cavity, which requires the use of linear response theory. We also show that our numerical calculations are in good agreement with the experimental data.
arxiv pdf