We are working on quantum computer architectures for two reasons
associated with the scale of devices: first, we now *have the
ability* to manipulate systems at the level of individual atoms
and particles, and doing so might bring us advances in computational
power for solving some problems; second, advances in Moore's Law will
bring traditional VLSI into the atomic scale in the coming years. The
video below gives an idea of the small scale of the phenomena we are
talking about.

An important tool in quantum mechanics is basic probability; the canonical example of a probabilistic classical variable is the roll of a die, as shown in the animation below.

In *superposition*, a quantum system may be partially
in one state, and partially in another. One aspect of this is that
the state of a quantum system in superposition is indeterminate; which
state we will find is a matter of probability.

The animation below shows *interference* of waves. The waves add up
in some places, and subtract in others. The same phenomenon applies
at the quantum mechanical level, and can be used to modify the
probability of a given state being measured. Managing interference is
the heart of quantum computing algorithms.

The video below shows *interference* of ocean waves off of
Inamuragasaki, near Kamakura, Japan. The waves add up in some places,
and subtract in others.

In *measurement*, the superposition of quantum system collapses
to a single value.

The video below shows how quantum effects in interferometry and the state collapse caused by which-path measurement can be used to do counter-intuitive things, including detecting whether a photon-sensitive bomb is live or a dud.

The video below shows how a single photon, or a stronger laser pulse, can interact with atoms held in two cavities, to generate entanglement. After interacting with the two atoms, the photon is measured. Typically, this measurement would tell us the parity of the two photons (even or odd). If the two atoms each started in a superposition state, some results will herald entanglement.

Entanglement can be used to *teleport* qubits from one location
to another.

Quantum effects can be used for either numeric quantum computation, or physical operations such as detection of eavesdropping.

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