Experimental orthogonalization of highly overlapping quantum states with single photons

Abstract

We experimentally realize a nonlinear quantum protocol on single-photon qubits with linear optical elements and appropriate measurements. The quantum nonlinearity is induced by post-selecting the polarization qubit based on a measurement result obtained on the spatial degree of freedom of the single photon which plays the role of a second qubit. Initially, both qubits are prepared in the same quantum state and an appropriate two-qubit unitary transformation entangles them before the measurement on the spatial part. We analyze the result by quantum state tomography on the polarization degree of freedom. We then demonstrate the usefulness of the protocol for quantum state discrimination by iteratively applying it on either one of two slightly different quantum states which rapidly converge to different orthogonal states by the iterative dynamics. Our work opens the door to employ effective quantum nonlinear evolution for quantum information processing.

Polaron formation in a spin chain by measurement-induced imaginary Zeeman field

“…This is because when we choose the initial state in a form (18) we effectively truncate dim H in expression (13) twice and do not change dim H ND . Exponential sensitivity to initial states is a characteristic feature 39,40 of non-unitary processes in quantum mechanics. Described here algorithm can be used to extract states being in the H ND from the initial superposition even for the cases of a small amplitude of such states.…”

Iterált harmadfokú kvantuminformatikai protokollok

“…Az így létrejövő folyamat megfeleltethető egy komplex polinomok hányadosaként előálló komplex függvény iterált dinamikájának, ha a qubitet egy komplex számmal reprezentáljuk, ezért bizonyos kezdőfeltételek esetén kaotikus viselkedésre vezet [2]. Az ilyen nemlineáris folyamatoknak számos kvantuminformatikai alkalmazása lehet, mint például a kvantumállapotok tisztítása [3] vagy a kvantumállapot-megkülönböztetés [4,5,6]. Egy másik, érzékenységükön alapuló gyakorlati felhasználásuk lehet a kvantum-áramkörök, kvantum-chipek tesztelése, a fellépő zaj és hibaforrások feltérképezése.…”