Yaron Kedem

Modular values and weak values of quantum observables.

The concept of a modular value of an observable of a pre- and postselected quantum system is introduced. It is similar in form and in some cases has a close connection to the weak value of an observable, but instead of describing an effective interaction when the coupling is weak, it describes a coupling of any strength but only to qubit meters. The generalization of the concept for a coupling of a composite system to a multiqubit meter provides an explanation of some current experiments.

Heisenberg-scaling measurement of the single-photon Kerr non-linearity using mixed states

Improving the precision of measurements is a significant scientific challenge. Previous works suggest that in a photon-coupling scenario the quantum fisher information shows a quantum-enhanced scaling of N2, which in theory allows a better-than-classical scaling in practical measurements. In this work, utilizing mixed states with a large uncertainty and a post-selection of an additional pure system, we present a scheme to extract this amount of quantum fisher information and experimentally attain a practical Heisenberg scaling. We performed a measurement of a single-photon’s Kerr non-linearity with a Heisenberg scaling, where an ultra-small Kerr phase of ≃6 × 10−8 rad was observed with a precision of ≃3.6 × 10−10 rad. From the use of mixed states, the upper bound of quantum fisher information is improved to 2N2. Moreover, by using an imaginary weak-value the scheme is robust to noise originating from the self-phase modulation.Quantum metrology usually relies on entanglement or squeezing for pursuing Heisenberg-limited precision. In this work, instead, the authors demonstrate Heisenberg-scaling measurement of a single photon Kerr’s nonlinearity using less-demanding mixed states.

Unusual superconducting isotope effect in the presence of a quantum criticality

The isotope effect in superconductivity (SC) is used to make a concrete connection to a quantum critical point (QCP) that is tunable by isotopic mass substitution. We find a distinct contribution t ...

Obtaining imaginary weak values with a classical apparatus: Applications for the time and frequency domains

Weak measurements with imaginary weak values are reexamined in light of recent experimental results. The shift of the meter, due to the imaginary part of the weak value, is derived via the probability of post-selection, which allows considering the meter as a distribution of a classical variable. The derivation results in a simple relation between the change in the distribution and its variance. By applying this relation to several experimental results, in which the meter involved the time and frequency domains, it is shown to be especially suitable for scenarios of that kind. The practical and conceptual implications of a measurement method, which is based on this relation, are discussed.