I spent some time playing around with
libquantum, the free quantum
simulation library, and created two musical compositions that
represent the inner workings of a quantum computer. So if you'd like
to know what a quantum computer sounds like, here's your chance!

The first composition is a setting of
Grover's
algorithm, telling
the heroic tale of the search for a record in a database. It closely
follows Grover's original proposal, with each note corresponding to
the addressing of a
qubit. So essentially, you
are listening to the music the programmer of the quantum computer
plays on his quantum keyboard. You can easily hear some distinctive
features of quantum algorithms. As a result of their reversible
nature, quantum algorithms have many repetitions of their basic
building blocks, which of course is also a common concept in
music. You might also notice that there are both sequences of single
notes and of chords. These correspond to single-qubit quantum gates
and multi-qubit quantum gates, respectively.

The second piece is about Shor's
algorithm for prime
factorization. The most obvious difference to the Grover track is that
it is much longer. Factorizing 15, which is the smallest number for
which Shor's algorithm can be used, already takes more than 4,000
quantum gates! The whole piece also sounds more complex, which is due
to the main operation, modular exponentiation, being fairly
sophisticated, even if you use the clever implementation by
Beckman et
al. Shortly before the
end (at 13:14), you can hear that a different part begins. This is the
quantum fourier transform, which takes much less time than the modular
exponentiation, but is the real deal-maker that renders Shor's
algorithm superior to its classical counterparts.

So how did I do it? First, I used libquantum's quantum object
code
interface
to cast the gate sequences for the demos shipped with libquantum into
a human-readable form. Then I wrote a small Perl script that converts
the quantum gates into musical notes, with each qubit addressed in a
gate corresponding to a different pitch. For both pieces I used a
pentatonic scale
in order to keep dissonances to a minimum. If you're interested you
can download the score files for
Grover's and
Shor's algorithm,
respectively. From these scores I created a MIDI file with
MIDI::Simple,
which were finally rendered by the
TiMidity++ software synth.

Copyright 2006--2011 Hendrik Weimer. This document is available under
the terms of the GNU Free Documentation License. See
the licensing terms for further details.