  Dissipationless quantum states, such as superconductivity and superfluidity,
have attracted interest for almost a century. A variety of systems exhibit
these macroscopic quantum phenomena, ranging from superconducting electrons in
metals to superfluid liquids, atomic vapours, and even large nuclei. It was
recently suggested that liquid metallic hydrogen could form two new unusual
dissipationless quantum states, namely the metallic superfluid and the
superconducting superfluid. Liquid metallic hydrogen is projected to occur only
at an extremely high pressure of about 400 GPa, while pressures on hydrogen of
320 GPa having already been reported. The issue to be adressed is if this state
could be experimentally observable in principle. We propose four experimental
probes for detecting it.
