41 research outputs found
Experimental verification of the commutation relation for Pauli spin operators using single-photon quantum interference
We report experimental verification of the commutation relation for Pauli
spin operators using quantum interference of the single-photon polarization
state. By superposing the quantum operations and on a single-photon polarization state, we have experimentally
implemented the commutator, , and the anticommutator,
, and have demonstrated the relative phase factor
of between and operations. The
experimental quantum operation corresponding to the commutator, , showed process fidelity of 0.94 compared to the ideal
operation and is determined to be .Comment: 4pages, 3 figure
Realizing Physical Approximation of the Partial Transpose
The partial transpose by which a subsystem's quantum state is solely
transposed is of unique importance in quantum information processing from both
fundamental and practical point of view. In this work, we present a practical
scheme to realize a physical approximation to the partial transpose using local
measurements on individual quantum systems and classical communication. We then
report its linear optical realization and show that the scheme works with no
dependence on local basis of given quantum states. A proof-of-principle
demonstration of entanglement detection using the physical approximation of the
partial transpose is also reported.Comment: 5 pages with appendix, 3 figure
Strong interactions between dipolar polaritons
Nonperturbative coupling between cavity photons and excitons leads to
formation of hybrid light-matter excitations termed polaritons. In structures
where photon absorption leads to creation of excitons with aligned permanent
dipoles, the elementary excitations, termed dipolar polaritons, are expected to
exhibit enhanced interactions. Here, we report a substantial increase in
interaction strength between dipolar polaritons as the size of the dipole is
increased by tuning the applied gate voltage. To this end, we use coupled
quantum well structures embedded inside a microcavity where coherent electron
tunneling between the wells controls the size of the excitonic dipole.
Modifications of the interaction strength are characterized by measuring the
changes in the reflected intensity of light when polaritons are driven with a
resonant laser. Factor of 6.5 increase in the interaction strength to linewidth
ratio that we obtain indicates that dipolar polaritons could be used to
demonstrate a polariton blockade effect and thereby form the building blocks of
many-body states of light.Comment: 12 pages, 4 figures. Supplementary not
Experimental Implementation of the Universal Transpose Operation
The universal transpose of quantum states is an anti-unitary transformation
that is not allowed in quantum theory. In this work, we investigate
approximating the universal transpose of quantum states of two-level systems
(qubits) using the method known as the structural physical approximation to
positive maps. We also report its experimental implementation in linear optics.
The scheme is optimal in that the maximal fidelity is attained and also
practical as measurement and preparation of quantum states that are
experimentally feasible within current technologies are solely applied.Comment: 4 pages, 4 figure