When we talk about the quantum world we are usually talking about quanta at the microscopic level.  There are though circumstances of large-scale (macroscopic) quantum mechanics.  These large-scale circumstances are usually discussed in terms of quantum coherence for such novel phenomena as lasers, holography, superconductivity and superfluidity.

What we are talking about in such circumstances is the coherent superposition of fields where the physical properties are typically uniform, in phase or coherent.  Most of these states happen at temperatures around 10-7K.  This is close to absolute zero and far from the temperatures we usually see in our environment everyday.  However, there are some areas in ceramics and lasers where this is not the case.  This has lead to speculations about what more we might discover and where else quantum coherence might be observed at higher temperatures.

With lasers we find a unique principal of time reversal in the area on non-linear optics.  A phase conjugate mirror is a nonlinear optical effect to precisely reverse the direction of propagation of each plane wave in an arbitrary beam of light, thereby causing the return beam to exactly retrace the path of the incident beam.  This is called wavefront reversal and is similar to holography (wavefront reconstruction) but is dynamic and not static.

Here is another way of thinking about such properties.  Imagine you are holding an inexpensive laser pointer in your hand and were to point it at a phase conjugate mirror.  No matter what angle you point the laser towards the mirror, the light will never reflect off of it at an incident angle. Instead it returns back to you or rather the laser.  In a way it appears to be absorbed 100 percent by the mirror rather than reflected – though such is not the case.

These techniques can be used to remove noise from within optical systems.  There is an area of advance study at DARPA using wavefront reversal to create retro-reflectors for the purpose of invisibility cloaks.