Macroscopic Quantum Dynamics
Macroscopic Quantum Dynamics
High-precision Torsional Oscillator Evidence for a ‘Superglass’ State in Solid 4He
Essence: Experiments with solid 4He confined to the hollow ring of a torsional oscillator at extremely low temperatures were interpreted in terms of an exotic supersolid phase—a crystalline solid that somehow flows like a superfluid. Our comprehensive study of the relaxation dynamics of the solid 4He torsional oscillator system using a high precision SQUID-based sensor, as a function of time and temperature, revealed an alternative explanation. The solid 4He dynamics evidences a “supersolid glass,” where glassy behavior of crystal dislocations and superfluidity could coexist. However, the former dominates the empirical data.
Measured frequency shift and dissipation detected in sold 4He at millikelvin temperature using SQUID based torsion oscillator (inset) operating in an ultralow vibration laboratory at T~20mK. The temperature and time evolution of these characteristics is most consistent with depinning and subsequent dynamics of crystal dislocations and not with a predominant supersolid component.
Superfluid DC-SQUID Detection of Quantum Interference of Superfluid 3He
Essence: Double-path quantum interference experiments have long demonstrated the quantum-wave nature of beams of electrons neutrons, and atoms etc. In condensed matter systems, double-path quantum interference is observed in the superconducting quantum interference device (DC-SQUID). In this project we invented a superfluid DC-SQUID: a double-path quantum interference experiment involving a liquid: superfluid 3He. In this first superfluid DC-SQUID the mass currents are measured using superconductive DC-SQUID techniques at temperatures near 100 μK; the quantum phase shift is controlled by using the rotation of the Earth. The classic interference pattern with periodicity determined by the 3He quantum of circulation is observed.
Left: Schematic topology and experimental geometry of a superfluid DC-SQUID based on two superfluid Josephson junctions in a closed loop operating in an ultralow vibration laboratory at T~100 μK. Right: Magnitude maximum of Josephson current through the superfluid DC-SQUID versus the component of Earth rotation vector threading it, measured in units of the superfluid circulation quantum. In perfect agreement with superfluid DC-SQUID theory.
Josephson Oscillations and Current-Phase Characteristic of Superfluid 3He
Nature 388, 449 (1997). Science278, 1435-1438 (1997).
Essence: Josephson quantum oscillations occur are that the two macroscopic quantum systems each have a well-defined quantum phase, φ, a different average energy per particle, μ, and that the wavefunctions describing the systems overlaps slightly: the frequency of the resulting oscillations is then given by f = (μ2− μ1)/h =P2m3/ρh, where h is Planck's constant m3 the mass of the helium atoms in liquid density ρ, and P the pressure difference across the junction. We reported the first observation of Josephson oscillating mass currents between two reservoirs of a superfluid (3He), the Josephson weak link being provided by an array of submicron apertures in a membrane separating the reservoirs. Subsequent analysis revealed the mass-current to quantum-phase characteristics of these first superfluid Josephson junctions.
Left: Schematic theory of Josephson oscillations as pressure across the superfluid Josephson junction (vertical axis) is reduced over time. Right: measured frequency of Josephson oscillations across superfluid Josephson junction operating in an ultralow vibration laboratory at T~500μK and above.