Home > English > Notes > Highlights > LPS Highlights 2010

Measuring the high frequency quantum fluctuations with an on-chip resonant circuit


Measuring the high frequency quantum fluctuations with an on-chip resonant circuit

The measurement of the current fluctuations of a conductor, the noise, is a powerful tool to study electronic transport. It can reveal the nature of electronic correlations or the value of the effective charge of the current carriers. When the frequency is of the order of the energy scales of the system, like the voltage V (energy eV) or the temperature T (energy kBT), the current fluctuations show a frequency dependence with signature of these energy scales. In the quantum regime, when the energy associated with the frequency hν is much higher than the thermal energy kBT, the noise can be describe as an exchange of photons of energy hν between the system under study and the noise detector. Depending on whether photons are emitted or absorbed by the source, one measures emission or absorption noise. This difference between emission and absorption processes is well known in quantum optics but difficult to observe in electric circuits.

 

 

Figure :(a) Differential conductance dI/dVD of the detector junction at different temperatures T. The peaks corresponding to the detection of emission or absorption noise are denoted by arrows. The curves are shifted vertically for clarity. (b) Dependence versus T of noise at 28.4GHz in emission and in absorption. The amplitude of the noise is extracted from the amplitude of the peaks of figure (a). Only absorption noise is detected below 0.4 K. The solid line corresponds to the theoretical predictions for the noise of a resistor at thermal equilibrium in the quantum regime.

 

Researchers of the Laboratoire de Physique des Solides managed to coupled with an on-chip superconducting resonant circuit a quantum detector of noise, a superconductor-insulator-superconductor junction able to distinguish between emission and absorption, and a Josephson junction, which corresponds to two superconductor separated by a small tunnel junctions. The emission and absorption noise of the resonant circuit was probed in the quantum regime at equilibrium. At low temperature the resonant circuit exhibits only absorption noise related to zero point fluctuations, whereas at higher temperature emission noise is also present. This technique allows also the direct measurement of the noise associated with the tunnelling of current carriers at 28.4GHz et 80.2 GHz, the resonance frequencies of the coupling circuit.

 

Measuring separately the emission and absorption noise at high frequency gives a new tool to understand electronic transport in mesoscopic devices.

 

Contacts : R. Deblock, H. Bouchiat

 

Reference : Emission and Absorption quantum noise measurement with an on-chip resonant circuit
J. Basset, H. Bouchiat, R. Deblock Phys. Rev. Lett. 105, 166801 (2010).