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Schrodinger's Cat -- The Movie

April 19, 2010 - 12:30pm
John Martinis
UC Santa Barbara

The thought experiment of Schrodinger's cat illustrates the wave-particle duality in quantum mechanics, which originates from the two distinct ways in which a quantum state may change: a linear (unitary) evolution according to the Schrodinger wave equation, and a nonlinear (projective or collapse) evolution due to measurement. A model system to observe this collapse is the harmonic oscillator, since a “Schrodinger's cat state” can be prepared as a superposition of coherent states, and its subsequent evolution becomes probabilistic due to system decoherence. Here we present a movie of the collapse of the cat state from a coherent to incoherent superposition, obtained by measuring the cat state during its decay for 60 time steps. Movies can be downloaded

The cat states are prepared by coupling a superconducting phase qubit to a high-Q coplanar wave guide resonator. The qubit is used to pump photons into the resonator and, subsequently, read out its state, and has been used previously to prepare and detect photon number states (Fock states). Using a generalization of this scheme by Law and Eberly, we can now create arbitrary quantum states of the photon field with up to approximately 10 photons: the deterministic synthesis of such states can be considered as the quantum version of a digital to analog converter. The states are analyzed by directly mapping out the corresponding Wigner function, which is the phase-space equivalent to the density matrix.

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