Quantum superposition of distinct macroscopic states

Abstract

In 1935, Schrodinger attempted to demonstrate the limitations of quantum mechanics using a thought experiment in which a cat is put in a quantum superposition of alive and dead states. The idea remained an academic curiosity until the 1980s when it was proposed that, under suitable conditions, a macroscopic object with many microscopic degrees of freedom could behave quantum mechanically, provided that it was sufficiently decoupled from its environment. Although much progress has been made in demonstrating the macroscopic quantum behaviour of various systems such as superconductors, nanoscale magnets, laser-cooled trapped ions, photons in a microwave cavity and C60 molecules, there has been no experimental demonstration of a quantum superposition of truly macroscopically distinct states. Here we present experimental evidence that a superconducting quantum interference device (SQUID) can be put into a superposition of two magnetic-flux states: one corresponding to a few microamperes of current flowing clockwise, the other corresponding to the same amount of current flowing anticlockwise.

Physics: Quantum all the way

“…But decoherence has also been watched in genuinely macroscopic objects: hoops of superconducting material. Superconductivity is an inherently quantummechanical behaviour, and electrical currents in a ring of superconducting material called a superconducting quantum interference device (SQUID) can be placed in a superposition of states that circulate in opposite directions 10,11 . These states can then be monitored by looking at the interference between them.…”

Phase Dynamics of Superconducting Junctions Under Microwave Excitation in Phase Diffusive Regime

“…The irradiating microwaves produced a photon-assisted JQP current at certain gate voltages, providing an estimation of the energy-level splitting between two macroscopic quantum states of charge coherently superposed by Josephson coupling. (Nakamura, Chen et al 1997) For the phase dominant systems, enhanced macroscopic quantum tunneling were observed in system of single Josephson junction (Martinis, Devoret et al 1985;Clarke, Cleland et al 1988) and superconducting quantum interference devices(SQUIDs) (Friedman, Patel et al 2000;van der Wal, Ter Haar et al 2000). Recently, devices based on Josephson junctions, such as SQUIDs, charge boxes, and single junctions have been demonstrated as an ideal artificial two-level system for quantum computation applications by using the microwave spectrometry.…”

Trace dynamics models with global supersymmetry

“…al. experiment [52] is roughly 8.6 × 10 −6 eV, and the circulating currents each correspond to the collective motion of ∼ 10 9 Cooper pairs. According to Eq.…”

“…Coherent superpositions of macroscopic states, involving large numbers of particles, will persist in time if the energy spread between the superimposed states is small enough. For example, consider the recent superconducting quantum interference device (SQUID) experiments [52] that observe the existence of coherent superpositions of macroscopic states consisting of oppositely circulating supercurrents. The variance ∆E in the Friedman et.…”