Liquid static Liquid moving An incoming quasiparticle has energy E 0 = ½m*v F 2. In the rest frame of the wire moving at v this energy appears to be E v = ½m*(v F 2 +v 2 ) = E 0 + m*v F v = E 0 + p F v Dispersion curve for 3 He quasiparticles – distortion with velocity

Liquid static Liquid moving The distortion of the dispersion curve provides an effective potential which limit the motion of (here) the rightward moving quasiparticles. Dispersion curve for 3 He quasiparticles – distortion with velocity

Normal reflection

Andreev reflection

Two features of the above we use for imaging. First, the effective potential created by a flow field does a number of remarkable things for us, and Secondly, the retroreflection behaviour of Andreev scattering does some quite magical things which we exploit.

Damping of a moving object

This gives MAXIMUM possible damping. and thus is amazingly sensitive to quasiparticle density (otherwise it would be pretty stupid trying to detect a quasiparticle gas equivalent to a pretty good vacuum by its damping on a moving object. also anything which interferes with this remarkable cancellation reduces damping, for example muddling the flow fields by immersing the moving object in a vortex tangle. (Thus we can use vibrating wire as local “one-pixel” camera.) But how about proper imaging?

The effective potential created by a vortex for an incoming particle (which is Andreev reflected on one side...

... but gets through with no problem on the other side. Thus vortices throw shadows when illuminated by qps.

The black body puts out its excitation beam.

Any vorticity then reflects the beam back into the radiator volume thus raising its temperature.

This shows the fraction of the excitation beam reflected back into the radiator cavity as a function of the velocity of the turbulence-generating wire outside.

PRL 93, (2004)

A typical value for the density in the middle of the figure (say 2x10 7 m -2 ) corresponds to a vortex separation of 0.2 mm, but we can easily resolve densities 20 times smaller than this, i.e. a separation of 1 mm. That is an unbelievably dilute tangle. In other words the 3 He turbulence video is not out of the question.

Dispersion curve for 3 He quasiparticles – distortion with velocity

First stage: make a beam with Shaun’s “Black Body Radiator”, which creates an image also by transmission.

What to use for sensors?

Our vibrating wires are too large for this use,

Our vibrating wires are too large for this use, so we switch to quartz tuning forks.