Mladen Pavičić

Resonance energy-exchange-free detection and “welcher Weg” experiment

Abstract It is shown that a monolithic total-internal-reflection resonator can be used for energy-exchange-free detections of objects without recoils. Related energy-exchange-free detection of “welcher Weg” is discussed and an experiment with an atom interferometer is proposed. The obtained results are in agreement with quantum theory.

Resonance interaction-free measurement

One can use a single optical cavity as the simplest possible resonator in order to ascertain the presence of an object with an arbitrarily low portion of an incoming laser beam. In terms of individual photons, each photon nonrepeatedly tests the object with an arbitrarily high probability of detecting its presence without interacting with it.

CLOSURE OF THE ENHANCEMENT AND DETECTION LOOPHOLES IN THE BELL THEOREM BY THE FOURTH ORDER INTERFERENCE WITH PHOTONS OF DIFFERENT COLOURS

Abstract A loophole-free Bell experiment requiring detection efficiency as low as 67% is proposed. The experiment uses different frequency photon interference of fourth order at an asymmetrical beam splitter and a resulting non-maximal entanglement.

A method for reaching detection efficiencies necessary for optical loophole-free Bell experiments

Abstract A method for preparing loophole-free four-photon Bell experiments which requires a detection efficiency of 67% is proposed. It enables realistic detection efficiencies of 75% at a visibility of 85%. Each of the two type-II crystals down converts one correlated photon pair and we entangle one photon from one pair with one photon from the other pair on a highly transparent beam splitter. The entanglement selects two other conjugate photons into a Bell state. Wide solid angles for the conjugate photons then enable us to collect close to 100% of them. The cases when both photon pairs come from only one of the two crystals are successfully taken into account. Hardys equalities are discussed.

Realistic Interaction-Free Detection of Objects in a Resonator

We propose a realistic device for detecting objects almost without transferring a single quantum of energy to them. The device can work with an efficiency close to 100% and relies on two detectors counting both presence and absence of the objects. Its possible usage in performing fundamental experiments as well as possible applications are discussed.

New classes of Kochen-Specker contextual sets

Finding Kochen-Specker contextual sets proves to be essential for quantum information and quantum computation in particular. It is therefore essential to find algorithms and programs which can generate arbitrary Kochen-Specker sets in a nearly-exhaustive manner. In this paper we present such generations for two new classes of Kochen-Specker sets. All sets from one of the classes are completely invisible to standard algorithms and programs from the literature as well as the upper part of sets from the second class. We also describe the methods and programs we used to obtain the sets on supercomputing clusters.

Can Two-Way Direct Communication Protocols Be Considered Secure?

We consider attacks on two-way quantum key distribution protocols in which an undetectable eavesdropper copies all messages in the message mode. We show that under the attacks, there is no disturbance in the message mode and that the mutual information between the sender and the receiver is always constant and equal to one. It follows that recent proofs of security for two-way protocols cannot be considered complete since they do not cover the considered attacks.

PRESELECTED QUANTUM OPTICAL CORRELATIONS

Two previously discovered effects in the intensity interference: a spin-correlation between formerly unpolarized photons and a spin entanglement at-a-distance between photons that nowhere interacted, have been used for a proposal of a new preselection experiment. The experiment puts together two photons from two independent singlets and makes them interfere at an asymmetrical beam splitter. A coincidental detection of two photons emerging from different sides of the beam splitter preselect their pair-companion photons (which nowhere cross each other’s path) into a nonmaximal singlet state. The quantum-mechanical nonlocality thus proves to be essentially a property of selection. This enables a loophole-free experimental disproof of local hidden-variable theories requiring detection efficiency as low as 67% and an exclusion of all nonlocal hidden-variable theories that rely on some kind of a physical entanglement by means of a common medium.