Quantum fluctuations in the chirped pendulum

K. W. Murch, R. Vijay, I. Barth, O. Naaman, J. Aumentado, L. Friedland, I. Siddiqi

Research output: Contribution to journalArticlepeer-review

38 Scopus citations


Anharmonic oscillators, such as the pendulum, are widely 1 used for precision measurement and to model nonlinear phenomena 2 . Fluctuations such as thermal or quantum mechanical noise can excite random motion in the oscillator, ultimately imposing a bound on measurement sensitivity. In systems where equilibrium is established with the environment, noise-induced broadening scales with the intensity of fluctuations. But how does noise affect an out-of-equilibrium oscillator where the motion is varied faster than energy is exchanged with the environment? We create such a scenario by applying fast, frequency-chirped voltage pulses to a nonlinear superconducting resonator where the ring-down time is longer than the pulse duration. Under these conditions, the circuit oscillates with either small or large amplitude depending on whether the drive voltage is below or above a critical value 3 . This phenomenon, known as autoresonance, is significant in planetary dynamics 4 and plasmas 5 , enables the excitation of particles in cyclotron accelerators 6 and may even be used to detect the state of a quantum two-level system 7 . Our results show that the amplitude of fluctuations determines the initial conditions of such a non-equilibrium oscillator and does not affect its time evolution.

Original languageAmerican English
Pages (from-to)105-108
Number of pages4
JournalNature Physics
Issue number2
StatePublished - Feb 2011

Bibliographical note

Funding Information:
We thank A. G. Shagalov, who developed the pseudospectral code used for solving the Liouville equation. This research was funded by the Office of the Director of National Intelligence (ODNI), Intelligence Advanced Research Projects Activity (IARPA), through the Army Research Office. All statements of fact, opinion or conclusions contained herein are those of the authors and should not be construed as representing the official views or policies of IARPA, the ODNI, or the US Government. R.V. acknowledges funding from AFOSR under Grant No FA9550-08-1-0104; I.B. and L.F. acknowledge support from the Israel Science Foundation under Grant No 451/10.


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