  With the rapidly growing interest in quantum computing also grows the
importance of securing these quantum computers from various physical attacks.
Constantly increasing qubit counts and improvements to the fidelity of the
quantum computers hold great promise for the ability of these computers to run
novel algorithms with highly sensitive intellectual property. However, in
today's cloud-based quantum computer setting, users lack physical control over
the computers. Physical attacks, such as those perpetrated by malicious
insiders in data centers, could be used to extract sensitive information about
the circuits being executed on these computers. Indeed, this work shows for the
first time that power-based side-channel attacks could be deployed against
quantum computers. Such attacks can be used to recover information about the
control pulses sent to these computers. By analyzing these control pulses,
attackers can reverse-engineer the equivalent gate-level description of the
circuits, and possibly even the secret algorithms being run. This work
introduces five new types of attacks, and evaluates them using control pulse
information available from cloud-based quantum computers. This work
demonstrates how and what circuits could be recovered, and then in turn how to
defend from the newly demonstrated side-channel attacks on quantum~computers.
