Maria Maffei

Energetic cost of measurements using quantum, coherent, and thermal light

  1. Xiayu Linpeng,
  2. Léa Bresque,
  3. Maria Maffei,
  4. Andrew N. Jordan,
  5. 4 Alexia Auffèves,
  6. and Kater W. Murch
Quantum measurements are basic operations that play a critical role in the study and application of quantum information. We study how the use of quantum, coherent, and classical thermal
states of light in a circuit quantum electrodynamics setup impacts the performance of quantum measurements, by comparing their respective measurement backaction and measurement signal to noise ratio per photon. In the strong dispersive limit, we find that thermal light is capable of performing quantum measurements with comparable efficiency to coherent light, both being outperformed by single-photon light. We then analyze the thermodynamic cost of each measurement scheme. We show that single-photon light shows an advantage in terms of energy cost per information gain, reaching the fundamental thermodynamic cost.
arxiv pdf

Energetics of a Single Qubit Gate

  1. Jeremy Stevens,
  2. Daniel Szombati,
  3. Maria Maffei,
  4. Cyril Elouard,
  5. Réouven Assouly,
  6. Nathanaël Cottet,
  7. Rémy Dassonneville,
  8. Quentin Ficheux,
  9. Stefan Zeppetzauer,
  10. Audrey Bienfait,
  11. Andrew N. Jordan,
  12. Alexia Auffèves,
  13. and Benjamin Huard
Qubits are physical, a quantum gate thus not only acts on the information carried by the qubit but also on its energy. What is then the corresponding flow of energy between the qubit
and the controller that implements the gate? Here we exploit a superconducting platform to answer this question in the case of a quantum gate realized by a resonant drive field. During the gate, the superconducting qubit becomes entangled with the microwave drive pulse so that there is a quantum superposition between energy flows. We measure the energy change in the drive field conditioned on the outcome of a projective qubit measurement. We demonstrate that the drive’s energy change associated with the measurement backaction can exceed by far the energy that can be extracted by the qubit. This can be understood by considering the qubit as a weak measurement apparatus of the driving field.
arxiv pdf