A. Ranadive

Implementation of pairwise longitudinal coupling in a three-qubit superconducting circuit

  1. Tanay Roy,
  2. Suman Kundu,
  3. Madhavi Chand,
  4. Sumeru Hazra,
  5. N. Nehra,
  6. R. Cosmic,
  7. A. Ranadive,
  8. Meghan P. Patankar,
  9. Kedar Damle,
  10. and R. Vijay
We present the „trimon“, a multi-mode superconducting circuit implementing three qubits with all-to-all longitudinal coupling. This always-on interaction enables simple
implementation of generalized controlled-NOT gates which form a universal set. Further, two of the three qubits are protected against Purcell decay while retaining measurability. We demonstrate high-fidelity state swapping operations between two qubits and characterize the coupling of all three qubits to a neighbouring transmon qubit. Our results offer a new paradigm for multi-qubit architecture with applications in quantum error correction, quantum simulations and quantum annealing.
arxiv pdf

A two-fold quantum delayed-choice experiment in a superconducting circuit

  1. K. Liu,
  2. Y. Xu,
  3. W. Wang,
  4. Shi-Biao Zheng,
  5. Tanay Roy,
  6. Suman Kundu,
  7. Madhavi Chand,
  8. A. Ranadive,
  9. R. Vijay,
  10. Y. P. Song,
  11. L. M. Duan,
  12. and L. Sun
We propose and experimentally demonstrate a two-fold quantum delayed-choice experiment where wave or particle nature of a superconducting interfering device can be post-selected twice
after the interferometer. The wave-particle complementarity is controlled by a quantum which-path detector (WPD) in a superposition of its on and off states implemented through a superconducting cavity. The WPD projected to its on state records which-path information, which manifests the particle nature and destroys the interference associated with wave nature of the system. In our experiment, we can recover the interference signal through a quantum eraser even if the WPD has selected out the particle nature in the first round of delayed-choice detection, showing that a quantum WPD adds further unprecedented controllability to test of wave-particle complementarity through the peculiar quantum delayed-choice measurements.
arxiv pdf

Broadband parametric amplification with impedance engineering: Beyond the gain-bandwidth product

  1. Tanay Roy,
  2. Suman Kundu,
  3. Madhavi Chand,
  4. Vadiraj A. M.,
  5. A. Ranadive,
  6. N. Nehra,
  7. Meghan P. Patankar,
  8. J. Aumentado,
  9. A. A. Clerk,
  10. and R. Vijay
We present an impedance engineered Josephson parametric amplifier capable of providing bandwidth beyond the traditional gain-bandwidth product. We achieve this by introducing a positive
linear slope in the imaginary component of the input impedance seen by the Josephson oscillator using a λ/2 transformer. Our theoretical model predicts an extremely flat gain profile with a bandwidth enhancement proportional to the square root of amplitude gain. We experimentally demonstrate a nearly flat 20 dB gain over a 640 MHz band, along with a mean 1-dB compression point of -110 dBm and near quantum-limited noise. The results are in good agreement with our theoretical model.
arxiv pdf