  In a recent Letter [PRL 101, 074101 (2008)], Kapulkin and Pattanayak
presented evidence that a quantum Duffing oscillator, sufficiently damped so
that it is not classically chaotic, becomes chaotic in the transition region
between quantum and classical motion. If true, this would be a striking result.
However, Kapulkin and Pattanayak did not calculate the Lyapunov exponent for
the system, usually regarded as the litmus-test of chaos. Here we perform this
calculation, which throws considerable doubt upon their conclusions.
