Andrew J. Kerman

Suppressing relaxation in superconducting qubits by quasiparticle pumping

  1. Simon Gustavsson,
  2. Fei Yan,
  3. Gianluigi Catelani,
  4. Jonas Bylander,
  5. Archana Kamal,
  6. Jeffrey Birenbaum,
  7. David Hover,
  8. Danna Rosenberg,
  9. Gabriel Samach,
  10. Adam P. Sears,
  11. Steven J. Weber,
  12. Jonilyn L. Yoder,
  13. John Clarke,
  14. Andrew J. Kerman,
  15. Fumiki Yoshihara,
  16. Yasunobu Nakamura,
  17. Terry P. Orlando,
  18. and William D. Oliver
Dynamical error suppression techniques are commonly used to improve coherence in quantum systems. They reduce dephasing errors by applying control pulses designed to reverse erroneous
coherent evolution driven by environmental noise. However, such methods cannot correct for irreversible processes such as energy relaxation. In this work, we investigate a complementary, stochastic approach to reducing errors: instead of deterministically reversing the unwanted qubit evolution, we use control pulses to shape the noise environment dynamically. In the context of superconducting qubits, we implement a pumping sequence to reduce the number of unpaired electrons (quasiparticles) in close proximity to the device. We report a 70% reduction in the quasiparticle density, resulting in a threefold enhancement in qubit relaxation times, and a comparable reduction in coherence variability.
arxiv pdf

Towards Outperforming Classical Algorithms with Analog Quantum Simulators

  1. Sarah Mostame,
  2. Joonsuk Huh,
  3. Christoph Kreisbeck,
  4. Andrew J. Kerman,
  5. Takatoshi Fujita,
  6. Alexander Eisfeld,
  7. and Alán Aspuru-Guzik
With quantum computers being out of reach for now, quantum simulators are the alternative devices for efficient and more exact simulation of problems that are challenging on conventional
computers. Quantum simulators are classified into analog and digital, with the possibility of constructing „hybrid“ simulators by combining both techniques. In this paper, we focus on analog quantum simulators of open quantum systems and address the limit that they can beat classical computers. In particular, as an example, we discuss simulation of the chlorosome light-harvesting antenna from green sulfur bacteria with over 250 phonon modes coupled to each electronic state. Furthermore, we propose physical setups that can be used to reproduce the quantum dynamics of a standard and multiple-mode Holstein model. The proposed scheme is based on currently available technology of superconducting circuits consist of flux qubits and quantum oscillators.
arxiv pdf

Quantum information processing using quasiclassical electromagnetic interactions between qubits and electrical resonators

  1. Andrew J. Kerman
Electrical resonators are widely used in quantum information processing with any qubits that are manipulated via electromagnetic interactions. In nearly all examples to date they are
engineered to interact with qubits via real or virtual exchange of (typically microwave) photons, and the resonator must therefore have both a high quality factor and strong quantum fluctuations, corresponding to the strong-coupling limit of cavity QED. Although great strides in the control of quantum information have been made using this so-called „circuit QED“ architecture, it also comes with some characteristic limitations. In this paper, we discuss a new paradigm for coupling qubits electromagnetically via resonators, in which the qubits do not exchange photons with the resonator, but instead where the qubits exert quasi-classical, effective „forces“ on it. We show how this type of interaction is similar to that induced between the internal state of a trapped atomic ion and its center-of-mass motion by the photon recoil momentum, and that the resulting multiqubit entangling operations are insensitive textit{both to the state of the resonator and to its quality factor}. The method we describe is potentially applicable to a variety of qubit modalities, including superconducting and semiconducting solid-state qubits, trapped molecular ions, and possibly even electron spins in solids.
arxiv pdf

Quantum simulator of an open quantum system using superconducting qubits: exciton transport in photosynthetic complexes

  1. Sarah Mostame,
  2. Patrick Rebentrost,
  3. Alexander Eisfeld,
  4. Andrew J. Kerman,
  5. Dimitris I. Tsomokos,
  6. and Alán Aspuru-Guzik
Open quantum system approaches are widely used in the description of physical, chemical and biological systems. A famous example is electronic excitation transfer in the initial stage
of photosynthesis, where harvested energy is transferred with remarkably high efficiency to a reaction center. This transport is affected by the motion of a structured vibrational environment, which makes simulations on a classical computer very demanding. Here we propose an analog quantum simulator of complex open system dynamics with a precisely engineered quantum environment. Our setup is based on superconducting circuits, a well established technology. As an example, we demonstrate that it is feasible to simulate exciton transport in the Fenna-Matthews-Olson photosynthetic complex. Our approach allows for a controllable single-molecule simulation and the investigation of energy transfer pathways as well as non-Markovian noise-correlation effects.
arxiv pdf