Broadband continuous variable entanglement generation using Kerr-free Josephson metamaterial

  1. Michael Perelshtein,
  2. Kirill Petrovnin,
  3. Visa Vesterinen,
  4. Sina Hamedani Raja,
  5. Ilari Lilja,
  6. Marco Will,
  7. Alexander Savin,
  8. Slawomir Simbierowicz,
  9. Robab Jabdaraghi,
  10. Janne Lehtinen,
  11. Leif Grönberg,
  12. Juha Hassel,
  13. Mika Prunnila,
  14. Joonas Govenius,
  15. Sorin Paraoanu,
  16. and Pertti Hakonen
Entangled microwave photons form a fundamental resource for quantum information processing and sensing with continuous variables. We use a low-loss Josephson metamaterial comprising
superconducting non-linear asymmetric inductive elements to generate frequency (colour) entangled photons from vacuum fluctuations at a rate of 11 mega entangled bits per second with a potential rate above gigabit per second. The device is operated as a traveling wave parametric amplifier under Kerr-relieving biasing conditions. Furthermore, we realize the first successfully demonstration of single-mode squeezing in such devices – 2.4±0.7 dB below the zero-point level at half of modulation frequency.

Low-noise on-chip coherent microwave source

  1. Chengyu Yan,
  2. Juha Hassel,
  3. Visa Vesterinen,
  4. Jinli Zhang,
  5. Joni Ikonen,
  6. Leif Grönberg,
  7. Jan Goetz,
  8. and Mikko Möttönen
The increasing need for scaling up quantum computers operating in the microwave domain calls for advanced approaches for control electronics. To this end, integration of components
at cryogenic temperatures hosting also the quantum devices seems tempting. However, this comes with the limitations of ultra-low power dissipation accompanied by stringent signal-quality requirements to implement quantum-coherent operations. Here, we present a device and a technique to provide coherent continuous-wave microwave emission. We experimentally verify that its operation characteristics accurately follow our introduced theory based on a perturbative treatment of the capacitively shunted Josephson junction as a gain element. From phase noise measurements, we evaluate that the infidelity of typical quantum gate operations owing to this cryogenic source is less than 0.1% up to 10-ms evolution times, which is well below the infidelity caused by dephasing of the state-of-the-art superconducting qubits. Our device provides a coherent tone of 25 pW, corresponding to the total power needed in simultaneous control of thousands of qubits. Thus, together with future cryogenic amplitude and phase modulation techniques, our results may open pathways for scalable cryogenic control systems for quantum processors.

Characterizing cryogenic amplifiers with a matched temperature-variable noise source

  1. Slawomir Simbierowicz,
  2. Visa Vesterinen,
  3. Joshua Milem,
  4. Aleksi Lintunen,
  5. Mika Oksanen,
  6. Leif Roschier,
  7. Leif Grönberg,
  8. Juha Hassel,
  9. David Gunnarsson,
  10. and Russell E. Lake
We present a cryogenic microwave noise source with characteristic impedance of 50 Ω that can be installed in a coaxial line of a cryostat. The bath temperature of the noise source
is continuously variable between 0.1 K and 5 K without causing significant back-action heating on the sample space. As a proof-of-concept experiment, we perform Y-factor measurements of an amplifier cascade that includes a traveling wave parametric amplifier and a commercial high electron mobility transistor amplifier. We observe system noise temperatures as low as 680+20−200 mK at 5.7 GHz corresponding to 1.5+0.1−0.7 excess photons. The system we present has immediate applications in the validation of solid-state qubit readout lines.

Fast control of dissipation in a superconducting resonator

  1. Vasilii Sevriuk,
  2. Kuan Yen Tan,
  3. Eric Hyyppä,
  4. Matti Silveri,
  5. Matti Partanen,
  6. Máté Jenei,
  7. Shumpei Masuda,
  8. Jan Goetz,
  9. Visa Vesterinen,
  10. Leif Grönberg,
  11. and Mikko Möttönen
We report on fast tunability of an electromagnetic environment coupled to a superconducting coplanar waveguide resonator. Namely, we utilize a recently-developed quantum-circuit refrigerator
(QCR) to experimentally demonstrate a dynamic tunability in the total damping rate of the resonator up to almost two orders of magnitude. Based on the theory it corresponds to a change in the internal damping rate by nearly four orders of magnitude. The control of the QCR is fully electrical, with the shortest implemented operation times in the range of 10 ns. This experiment constitutes a fast active reset of a superconducting quantum circuit. In the future, a similar scheme can potentially be used to initialize superconducting quantum bits.

Advanced Concepts in Josephson Junction Reflection Amplifiers

  1. Pasi Lähteenmäki,
  2. Visa Vesterinen,
  3. Juha Hassel,
  4. G. S. Paraoanu,
  5. Heikki Seppä,
  6. and Pertti Hakonen
Low-noise amplification atmicrowave frequencies has become increasingly important for the research related to superconducting qubits and nanoelectromechanical systems. The fundamental
limit of added noise by a phase-preserving amplifier is the standard quantum limit, often expressed as noise temperature Tq=ℏω/2kB. Towards the goal of the quantum limit, we have developed an amplifier based on intrinsic negative resistance of a selectively damped Josephson junction. Here we present measurement results on previously proposed wide-band microwave amplification and discuss the challenges for improvements on the existing designs. We have also studied flux-pumped metamaterial-based parametric amplifiers, whose operating frequency can be widely tuned by external DC-flux, and demonstrate operation at 2ω pumping, in contrast to the typical metamaterial amplifiers pumped via signal lines at ω.