Amazing Coincidences

Ian Stewart

S. P. Kulik, S. N. Molotkov

The security of the measurement-device-independent quantum key distribution protocol through untrusted nodes has been directly proven using fundamental entropy uncertainty relations. Reasons for the amazing coincidence of the expressions for the secrete key length in the BB84 and MDI protocols are presented.

Partha Ghose, Sudip Patra

The phase space representation is used in the classical mechanics of particles but is not appropriate for describing interference phenomena that occur in classical field theory such as classical optics. The methods of classical optics and quantum mechanics are amazingly similar. That is principally because both use Hilbert spaces to represent states. The only difference is in the use of non-commuting operators to represent observables in quantum mechanics. The quantum theory of light predicts perfect anti-coincidence for single detections on the two sides of a beam splitter, whereas classical light, however weak, would be divided on a beam splitter and produce a minimum degree of correlated or coincidence counts. In mathematics the Hermite polynomials are classical orthogonal polynomial sequences that arise in probability and numerical analysis as Gaussian quadrature. They are also used in systems theory in connection with non-linear operations on Gaussian noise and other sciences.

Holger Friedrich

Iulia Georgescu

R. Engeln, Giel Berden, Rudy Peeters +1 more

It is experimentally demonstrated that a narrow band continuous wave (cw) light source can be used in combination with a high-finesse optically stable cavity to perform sensitive, high-resolution direct absorption and optical rotation spectroscopy in an amazingly simple experimental setup, using ideas from the field of cavity ring down spectroscopy. Light from a scanning narrow band cw laser is coupled into the cavity via accidental coincidences of the laser frequency with the frequency of one of the multitude of modes of the cavity. The absorption and polarization rotation information is extracted from a measurement of the time-integrated light intensity leaking out of the cavity as a function of laser wavelength.