Nicolas Bourlet

Microwave photon-number amplification

  1. Romain Albert,
  2. Joël Griesmar,
  3. Florian Blanchet,
  4. Ulrich Martel,
  5. Nicolas Bourlet,
  6. and Max Hofheinz
So far, quantum-limited power meters are not available in the microwave domain, hindering measurement of photon number in itinerant quantum states. On the one hand, single photon detectors
accurately detect single photons, but saturate as soon as two photons arrive simultaneously. On the other hand, more linear watt meters, such as bolometers, are too noisy to accurately detect single microwave photons. Linear amplifiers probe non-commuting observables of a signal so that they must add noise and cannot be used to detect single photons, either. Here we experimentally demonstrate a microwave photon-multiplication scheme which combines the advantages of a single photon detector and a power meter by multiplying the incoming photon number by an integer factor. Our first experimental implementation achieves a n = 3-fold multiplication with 0.69 efficiency in a 116 MHz bandwidth up to a input photon rate of 400 MHz. It loses phase information but does not require any dead time or time binning. We expect an optimised device cascading such multipliers to achieve number-resolving measurement of itinerant photons with low dark count, which would offer new possibilities in a wide range of quantum sensing and quantum computing applications.
arxiv pdf

Absence of a dissipative quantum phase transition in Josephson junctions

  1. Anil Murani,
  2. Nicolas Bourlet,
  3. Hélène le Sueur,
  4. Fabien Portier,
  5. Carles Altimiras,
  6. Daniel Esteve,
  7. Hermann Grabert,
  8. Jürgen Stockburger,
  9. and Philippe Joyez
Half a century after its discovery, the Josephson junction has become the most important nonlinear quantum electronic component at our disposal. It has helped reshaping the SI system
around quantum effects and is used in scores of quantum devices. By itself, the use of Josephson junctions in the Volt metrology seems to imply an exquisite understanding of the component in every aspects. Yet, surprisingly, there have been long-standing subtle issues regarding the modeling of the interaction of a junction with its electromagnetic environment which has generated broadly accepted misconceptions and paradoxical predictions. Here, we invalidate experimentally one such prediction, namely that a Josephson junction connected to a resistor becomes insulating beyond a given value of the resistance, due to a dissipative quantum phase transition. Our work clarifies how this key quantum component should be modeled and resolves contradictions in the theory.
arxiv pdf