Experimental violation of a Bell-Leggett-Garg inequality using weak measurements, Part I: Avoiding loopholes
ORAL
Abstract
We demonstrate the violation of a hybrid Bell-Leggett-Garg inequality that avoids both the disjoint sampling and fair sampling loopholes that are common to traditional Bell inequalities. Our algorithm uses sequential weak measurements of a Bell state that are implemented with four superconducting Xmon qubits. In this first of two talks, we detail the high-fidelity partial projections that are needed for this violation, which are realized by entangling an ancilla qubit to each data qubit using a controlled-Z two-qubit gate. After calibration of the ancilla readout, these partial projections indirectly measure qubit expectation values with a tunable amount of state disturbance. For sufficiently weak disturbance, the inequality can be violated using all the data collected in a single configuration.
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