Giovanna Tancredi

Quantum approximate optimization of the exact-cover problem on a superconducting quantum processor

  1. Andreas Bengtsson,
  2. Pontus Vikstål,
  3. Christopher Warren,
  4. Marika Svensson,
  5. Xiu Gu,
  6. Anton Frisk Kockum,
  7. Philip Krantz,
  8. Christian Križan,
  9. Daryoush Shiri,
  10. Ida-Maria Svensson,
  11. Giovanna Tancredi,
  12. Göran Johansson,
  13. Per Delsing,
  14. Giulia Ferrini,
  15. and Jonas Bylander
Present-day, noisy, small or intermediate-scale quantum processors—although far from fault-tolerant—support the execution of heuristic quantum algorithms, which might enable
a quantum advantage, for example, when applied to combinatorial optimization problems. On small-scale quantum processors, validations of such algorithms serve as important technology demonstrators. We implement the quantum approximate optimization algorithm (QAOA) on our hardware platform, consisting of two transmon qubits and one parametrically modulated coupler. We solve small instances of the NP-complete exact-cover problem, with 96.6\% success probability, by iterating the algorithm up to level two.
arxiv pdf

Direct spectrum analysis using a threshold detector with application to a superconducting circuit

  1. Grégoire Ithier,
  2. Giovanna Tancredi,
  3. and Phil Meeson
We introduce a new and quantitative theoretical framework for noise spectral analysis using a threshold detector, which is then applied to a superconducting device: the Cavity BifurcationAmplifier (CBA). We show that this new framework provides direct access to the environmental noise spectrum with a sensitivity approaching the standard quantum limit of weak continuous measurements. In addition, the accessible frequency range of the spectrum is, in principle, limited only by the ring down time of the resonator. This on-chip noise detector is non-dissipative and works with low probing powers, allowing it to be operated at low temperatures (T<10mK). We exploit this technique for measuring the frequency fluctuations of the CBA and find a low frequency noise with an amplitude and spectrum compatible with a dielectric origin.[/expand]
arxiv pdf