Quantum computer simulator

The simulator below implements a modified (compiled) version of Grover's search algorithm.  Operations in the algorithm that are not needed for this small database have been removed. The first experimental implementation of a scheme like this was performed by Paul Kwiat's group

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Java applet showing an optical quantum computer simulator.

The beam splitters direct a single photon from the laser along 4 paths simultaneously.  In each path is an object.  One of the objects (coloured light blue) shifts the phase of the photon wave by 180o.   This is the object we are searching for.  

In the simulator, any photon wave which is shifted in phase by 180o is shown as a blue wave.

The 4 paths are combined by various beam splitters.  Destructive and constructive interference at the beam splitters changes the direction the photon. A single photon emerges at an output corresponding to the position of the hidden object.

Select a position of the (light blue) object and see how interference ensures that the photon emerges from the correct output.  

Note that only a single photon is needed to find the position of the object.  The photon effectively samples all paths simultaneously.