John M. Martinis

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

Direct Wigner tomography of a superconducting anharmonic oscillator

  1. Yoni Shalibo,
  2. Roy Resh,
  3. Ofer Fogel,
  4. David Shwa,
  5. Radoslaw Bialczak,
  6. John M. Martinis,
  7. and Nadav Katz
The analysis of wave-packet dynamics may be greatly simplified when viewed in phase-space. While harmonic oscillators are often used as a convenient platform to study wave-packets,
arbitrary state preparation in these systems is more challenging. Here, we demonstrate a direct measurement of the Wigner distribution of complex photon states in an anharmonic oscillator – a superconducting phase circuit, biased in the small anharmonicity regime. We test our method on both non-classical states composed of two energy eigenstates and on the dynamics of a phase-locked wavepacket. This method requires a simple calibration, and is easily applicable in our system out to the fifth level.
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