Quantum and Classical Chirps in an Anharmonic Oscillator

TL;DR

This study investigates the dynamics of a tunable anharmonic quantum system under frequency-chirped excitation, revealing classical-like wavepacket behavior at low anharmonicity and discrete energy level excitation at high anharmonicity, with a transition mapped between these regimes.

Contribution

It provides the first detailed experimental mapping of the transition between classical and quantum responses in a tunable anharmonic oscillator.

Findings

Exponential enhancement of lifetimes for highly excited states at low anharmonicity.

Observation of sharp energy level excitations at high anharmonicity.

Mapping of the transition threshold between classical and quantum regimes.

Abstract

We measure the state dynamics of a tunable anharmonic quantum system, the Josephson phase circuit, under the excitation of a frequency-chirped drive. At small anharmonicity, the state evolves like a wavepacket - a characteristic response in classical oscillators; in this regime we report exponentially enhanced lifetimes of highly excited states, held by the drive. At large anharmonicity, we observe sharp steps, corresponding to the excitation of discrete energy levels. The continuous transition between the two regimes is mapped by measuring the threshold of these two effects.