Efficient Quantum-State Estimation by Continuous Weak Measurement and Dynamical Control

 

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Greg A. Smith, Andrew Silberfarb, Ivan H. Deutsch, and Poul S. Jessen
 

We demonstrate a fast, robust, and nondestructive protocol for quantum-state estimation based on continuous weak measurement in the presence of a controlled dynamical evolution. Our experiment uses optically probed atomic spins as a test bed and successfully reconstructs a range of trial states with fidelities of ~90%. The procedure holds promise as a practical diagnostic tool for the study of complex quantum dynamics, the testing of quantum hardware, and as a starting point for new types of quantum feedback control.
 

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Lattice of double wells for manipulating pairs of cold atoms

 

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Sebby-Strabley J, Anderlini M, Jessen PS, Porto JV
 

We describe the design and implementation of a two-dimensional optical lattice of double wells suitable for isolating and manipulating an array of individual pairs of atoms in an optical lattice. Atoms in the square lattice can be placed in a double well with any of their four nearest neighbors. The properties of the double well the barrier height and relative energy offset of the paired sites can be dynamically controlled. The topology of the lattice is phase stable against phase noise imparted by vibrational noise on mirrors. We demonstrate the dynamic control of the lattice by showing the coherent splitting of atoms from single wells into double wells and observing the resulting double-slit atom diffraction pattern. This lattice can be used to test controlled neutral atom motion among lattice sites and should allow for testing controlled two-qubit gates.
 

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A Continuous Non-demolition Measurement of the Cs Clock Transition Pseudo-spin

 

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Souma Chaudhury, Greg A. Smith, Kevin Schulz and Poul S. Jessen
 

We demonstrate a weak continuous measurement of the pseudo-spin associated with the clock transition in a sample of Cs atoms. Our scheme uses an optical probe tuned near the D1 transition to measure the sample birefringence, which depends on the z-component of the collective pseudospin. At certain probe frequencies the differential light shift of the clock states vanishes and the measurement is non-perturbing. In dense samples the measurement can be used to squeeze the collective clock pseudo-spin, and has potential to improve the performance of atomic clocks and interferometers.
 

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