Pertti Hakonen

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.
arxiv pdf

Coherence from vacuum fluctuations

  1. Pasi Lähteenmäki,
  2. G. S. Paraoanu,
  3. Juha Hassel,
  4. and Pertti Hakonen
The existence of vacuum fluctuations is one of the most important predictions of modern quantum field theory. In the vacuum state, fluctuations occurring at different frequencies are
uncorrelated. However, if a parameter in the Lagrangian of the field is modulated by an external pump, vacuum fluctuations stimulate spontaneous downconversion processes, creating squeezing between modes symmetric with respect to half of the frequency of the pump. Here we show that by double parametric pumping of a superconducting microwave cavity in the ground state, it is possible to generate another fundamental type of correlation, namely coherence between photons in separate frequency modes that are not directly connected through a single downconversion process. The coherence is tunable by the phases of the pumps and it is established by a quantum fluctuation that takes simultaneously part in creation of two photon pairs. Our analysis indicates that the origin of this vacuum-induced coherence is the absence of „which-way“ information in the frequency space.
arxiv pdf

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.
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

Dielectric losses in multi-layer Josephson junction qubits

  1. David Gunnarsson,
  2. Juha-Matti Pirkkalainen,
  3. Jian Li,
  4. Gheorghe Sorin Paraoanu,
  5. Pertti Hakonen,
  6. Mika Sillanpää,
  7. and Mika Prunnila
We have measured the excited state lifetimes in Josephson junction phase and transmon qubits, all of which were fabricated with the same scalable multi-layer process. We have compared
the lifetimes of phase qubits before and after removal of the isolating dielectric, SiNx, and find a four-fold improvement of the relaxation time after the removal. Together with the results from the transmon qubit and measurements on coplanar waveguide resonators, these measurements indicate that the lifetimes are limited by losses from the dielectric constituents of the qubits. We have extracted the individual loss contributions from the dielectrics in the tunnel junction barrier, AlOx, the isolating dielectric, SiNx, and the substrate, Si/SiO2, by weighing the total loss with the parts of electric field over the different dielectric materials. Our results agree well and complement the findings from other studies, demonstrating that superconducting qubits can be used as a reliable tool for high-frequency characterization of dielectric materials. We conclude with a discussion of how changes in design and material choice could improve qubit lifetimes up to a factor of four.
arxiv pdf