Mika A. Sillanpaa

Near-ground state cooling in electromechanics using measurement-based feedback and Josephson parametric amplifier

  1. Ewa Rej,
  2. Richa Cutting,
  3. Debopam Datta,
  4. Nils Tiencken,
  5. Joonas Govenius,
  6. Visa Vesterinen,
  7. Yulong Liu,
  8. and Mika A. Sillanpää
Feedback-based control of nano- and micromechanical resonators can enable the study of macroscopic quantum phenomena and also sensitive force measurements. Here, we demonstrate the
feedback cooling of a low-loss and high-stress macroscopic SiN membrane resonator close to its quantum ground state. We use the microwave optomechanical platform, where the resonator is coupled to a microwave cavity. The experiment utilizes a Josephson travelling wave parametric amplifier, which is nearly quantum-limited in added noise, and is important to mitigate resonator heating due to system noise in the feedback loop. We reach a thermal phonon number as low as 1.6, which is limited primarily by microwave-induced heating. We also discuss the sideband asymmetry observed when a weak microwave tone for independent readout is applied in addition to other tones used for the cooling. The asymmetry can be qualitatively attributed to the quantum-mechanical imbalance between emission and absorption. However, we find that the observed asymmetry is only partially due to this quantum effect. In specific situations, the asymmetry is fully dominated by a cavity Kerr effect under multitone irradiation.
arxiv pdf

Coupling high-overtone bulk acoustic wave resonators via superconducting qubits

  1. Wayne Crump,
  2. Alpo Välimaa,
  3. and Mika A. Sillanpää
In this work, we present a device consisting of two coupled transmon qubits, each of which are coupled to an independent high-overtone bulk acoustic wave resonator (HBAR). Both HBAR
resonators support a plethora of acoustic modes, which can couple to the qubit near resonantly. We first show qubit-qubit interaction in the multimode system, and finally quantum state transfer where an excitation is swapped from an HBAR mode of one qubit, to an HBAR mode of the other qubit.
arxiv pdf

Dynamical Autler-Townes control of a phase qubit

  1. Jian Li,
  2. G. S. Paraoanu,
  3. Katarina Cicak,
  4. Fabio Altomare,
  5. Jae I. Park,
  6. Raymond W. Simmonds,
  7. Mika A. Sillanpaa,
  8. and Pertti J. Hakonen
Routers, switches, and repeaters are essential components of modern information-processing systems. Similar devices will be needed in future superconducting quantum computers. In this
work we investigate experimentally the time evolution of Autler-Townes splitting in a superconducting phase qubit under the application of a control tone resonantly coupled to the second transition. A three-level model that includes independently determined parameters for relaxation and dephasing gives excellent agreement with the experiment. The results demonstrate that the qubit can be used as a ON/OFF switch with 100 ns operating time-scale for the reflection/transmission of photons coming from an applied probe microwave tone. The ON state is realized when the control tone is sufficiently strong to generate an Autler-Townes doublet, suppressing the absorption of the probe tone photons and resulting in a maximum of transmission.
arxiv pdf