Matteo Mariantoni

Multiphoton Quantum Logic Gates for Superconducting Resonators with Tunable Nonlinear Interaction

  1. Frederick W. Strauch,
  2. and Matteo Mariantoni
We propose a tunable nonlinear interaction for the implementation of quantum logic operations on pairs of superconducting resonators, where the two-resonator interaction is mediated
by a transmon quantum bit (qubit). This interaction is characterized by a high on-to-off coupling ratio and allows for fast qubit-type and d-level system (qudit)-type operations for quantum information processing with multiphoton cavity states. We present analytical and numerical calculations showing that these operations can be performed with practically unit fidelity in absence of any dissipative phenomena, whereas physical two-photon two-resonator operations can be realized with a fidelity of 99.9% in presence of qubit and resonator decoherence. The resonator-qubit-resonator system proposed in this Letter can be implemented using available planar or three-dimensional microwave technology.
arxiv pdf

Simulating weak localization using superconducting quantum circuits

  1. Yu Chen,
  2. P. Roushan,
  3. D. Sank,
  4. C. Neill,
  5. Erik Lucero,
  6. Matteo Mariantoni,
  7. R. Barends,
  8. B. Chiaro,
  9. J. Kelly,
  10. A. Megrant,
  11. J. Y. Mutus,
  12. P. J. J. O'Malley,
  13. A. Vainsencher,
  14. J. Wenner,
  15. T. C. White,
  16. Yi Yin,
  17. A. N. Cleland,
  18. and John M. Martinis
Understanding complex quantum matter presents a central challenge in condensed matter physics. The difficulty lies in the exponential scaling of the Hilbert space with the system size,
making solutions intractable for both analytical and conventional numerical methods. As originally envisioned by Richard Feynman, this class of problems can be tackled using controllable quantum simulators. Despite many efforts, building an quantum emulator capable of solving generic quantum problems remains an outstanding challenge, as this involves controlling a large number of quantum elements. Here, employing a multi-element superconducting quantum circuit and manipulating a single microwave photon, we demonstrate that we can simulate the weak localization phenomenon observed in mesoscopic systems. By engineering the control sequence in our emulator circuit, we are also able to reproduce the well-known temperature dependence of weak localization. Furthermore, we can use our circuit to continuously tune the level of disorder, a parameter that is not readily accessible in mesoscopic systems. By demonstrating a high level of control and complexity, our experiment shows the potential for superconducting quantum circuits to realize scalable quantum simulators.
arxiv pdf

Excitation of superconducting qubits from hot non-equilibrium quasiparticles

  1. J. Wenner,
  2. Yi Yin,
  3. Erik Lucero,
  4. R. Barends,
  5. Yu Chen,
  6. B. Chiaro,
  7. J. Kelly,
  8. M. Lenander,
  9. Matteo Mariantoni,
  10. A. Megrant,
  11. C. Neill,
  12. P. J. J. O'Malley,
  13. D. Sank,
  14. A. Vainsencher,
  15. H. Wang,
  16. T. C. White,
  17. A. N. Cleland,
  18. and John M. Martinis
Superconducting qubits probe environmental defects such as non-equilibrium quasiparticles, an important source of decoherence. We show that „hot“ non-equilibrium quasiparticles,
with energies above the superconducting gap, affect qubits differently from quasiparticles at the gap, implying qubits can probe the dynamic quasiparticle energy distribution. For hot quasiparticles, we predict a non-neligable increase in the qubit excited state probability P_e. By injecting hot quasiparticles into a qubit, we experimentally measure an increase of P_e in semi-quantitative agreement with the model.
arxiv pdf

Controlled catch and release of microwave photon states

  1. Yi Yin,
  2. Yu Chen,
  3. Daniel Sank,
  4. P. J. J. O'Malley,
  5. T. C. White,
  6. R. Barends,
  7. J. Kelly,
  8. Erik Lucero,
  9. Matteo Mariantoni,
  10. A. Megrant,
  11. C. Neill,
  12. A. Vainsencher,
  13. J. Wenner,
  14. Alexander N. Korotkov,
  15. A. N. Cleland,
  16. and John M. Martinis
, in which the resonant cavity confines photons and promotes"]strong light-matter interactions. The cavity end-mirrors determine the performance of the coupled system, with higher mirror reflectivity yielding better quantum coherence, but higher mirror transparency giving improved measurement and control, forcing a compromise. An alternative is to control the mirror transparency, enabling switching between long photon lifetime during quantum interactions and large signal strength when performing measurements. Here we demonstrate the superconducting analogue, using a quantum system comprising a resonator and a qubit, with variable coupling to a measurement transmission line. The coupling can be adjusted through zero to a photon emission rate 1,000 times the intrinsic photon decay rate. We use this system to control photons in coherent states as well as in non-classical Fock states, and dynamically shape the waveform of released photons. This has direct applications to circuit quantum electrodynamics [3], and may enable high-fidelity quantum state transfer between distant qubits, for which precisely-controlled waveform shaping is a critical and non-trivial requirement [4, 5].
arxiv pdf

Computing prime factors with a Josephson phase qubit quantum processor

  1. Erik Lucero,
  2. Rami Barends,
  3. Yu Chen,
  4. Julian Kelly,
  5. Matteo Mariantoni,
  6. Anthony Megrant,
  7. Peter O'Malley,
  8. Daniel Sank,
  9. Amit Vainsencher,
  10. James Wenner,
  11. Ted White,
  12. Yi Yin,
  13. Andrew N. Cleland,
  14. and John M. Martinis
. Compiled versions of Shor’s algorithm have been demonstrated"]on ensemble quantum systems[2] and photonic systems[3-5], however this has yet to be shown using solid state quantum bits (qubits). Two advantages of superconducting qubit architectures are the use of conventional microfabrication techniques, which allow straightforward scaling to large numbers of qubits, and a toolkit of circuit elements that can be used to engineer a variety of qubit types and interactions[6, 7]. Using a number of recent qubit control and hardware advances [7-13], here we demonstrate a nine-quantum-element solid-state QuP and show three experiments to highlight its capabilities. We begin by characterizing the device with spectroscopy. Next, we produces coherent interactions between five qubits and verify bi- and tripartite entanglement via quantum state tomography (QST) [8, 12, 14, 15]. In the final experiment, we run a three-qubit compiled version of Shor’s algorithm to factor the number 15, and successfully find the prime factors 48% of the time. Improvements in the superconducting qubit coherence times and more complex circuits should provide the resources necessary to factor larger composite numbers and run more intricate quantum algorithms.
arxiv pdf