  The simple circadian oscillator found in cyanobacteria can be reconstituted
in vitro using three proteins-KaiA, KaiB and KaiC. The total phosphorylation
level of KaiC oscillates with a circadian period. Recent experiments elucidated
the structure and function of the cyanobacterial circadian oscillator, which is
driven by sunlight intensity variation and therefore by Earth's rotation. In
this paper, we derive the oscillator's equation of motion directly from
experimental data, couple it with Earth's rotation and compute its natural
periods and resonance curve. Finally, we propose the use of a quantum circuit
that is capable of describing the function of the oscillator.
