Multiphoton interference reveals strictly nonclassical phenomena. Its applications range
from fundamental tests of quantum mechanics to photonic quantum information processing …

We describe in detail the theory underpinning the measurement of density matrices of a pair
of quantum two-level systems (“qubits”). Our particular emphasis is on qubits realized by the …

Deterministic quantum computation with one pure qubit (DQC1) is an efficient model of
computation that uses highly mixed states. Unlike pure-state models, its power is not derived …

We experimentally demonstrate the first quantum system entangled in every degree of
freedom (hyperentangled). Using pairs of photons produced in spontaneous parametric …

We investigate the relationship between mixedness and entanglement for Gaussian states
of continuous variable systems. We introduce generalized entropies based on Schatten p …

We demonstrate complete characterization of a two-qubit entangling process—a linear
optics controlled-not gate operating with coincident detection—by quantum process …

Entanglement is one of the essential resources of quantum information and communication
technology. Photons are the most popular and promising media to manipulate …

We describe the operation and tolerances of a nondeterministic, coincidence basis,
quantum controlled-NOT gate for photonic qubits. It is constructed solely from linear optical …

Measurement connects the world of quantum phenomena to the world of classical events. It
has both a passive role—in observing quantum systems—and an active one, in preparing …

Ascertaining the physical state of a system is vital in order to understand and predict its
behaviour. However, due to their fragile nature, the direct observation of quantum states has …