We report the first state-independent experimental test of quantum contextuality on a single photonic qutrit (three-dimensional system), based on a recent theoretical proposal [Phys. Rev. Lett. 108, 030402 (2012)]. Our experiment spotlights quantum contextuality in its most basic form, in a way that is independent of either the state or the tensor product structure of the system.

No abstract

The router is a key element for a network. We describe a scheme to realize genuine quantum routing of single-photon pulses based on cascading of conditional quantum gates in a Mach-Zehnder interferometer and report a proof-of-principle experiment for its demonstration using linear optics quantum gates. The polarization of the control photon routes in a coherent way the path of the signal photon while preserving the qubit state of the signal photon represented by its polarization. We demonstrate quantum nature of this router by showing entanglement generated between the initially unentangled control and signal photons, and confirm that the qubit state of the signal photon is well preserved by the router through quantum process tomography.

No abstract

Quantum entanglement, the essential resource for quantum information processing, has rich dynamics under different environments. Probing different entanglement dynamics typically requires exquisite control of complicated system-environment coupling in real experimental systems. Here, by a simple control of the effective solid-state spin bath in a diamond sample, we observe rich entanglement dynamics, including the conventional asymptotic decay as well as the entanglement sudden death, a term coined for the phenomenon of complete disappearance of entanglement after a short finite time interval. Furthermore, we observe counter-intuitive entanglement rebirth after its sudden death in the same diamond sample by tuning an experimental parameter, demonstrating that we can conveniently control the non-Markovianity of the system-environment coupling through a natural experimental knob. Further tuning of this experimental knob can make the entanglement dynamics completely coherent under the same environmental coupling. Probing of entanglement dynamics, apart from its fundamental interest, may find applications in quantum information processing through control of the environmental coupling.Besides its significance as a fundamental concept in quantum mechanics, entanglement has been recognized as an essential resource for quantum computation and communication [1][2][3][4]. In any real experimental system, due to its inevitable coupling to the surrounding environment, entanglement degrades with time, leading to various kinds of entanglement dynamics under different environmental couplings [5][6][7][8][9]. The most common one is the asymptotic decay of the entanglement, where the entanglement approaches zero (typically exponentially) as the time goes to infinity. This behavior is similar to the quantum coherence decay and arises when the environmental coupling is dominated by pure dephasing [5,6]. Under more complicated dissipation, entanglement may completely vanish in a finite (typically short) time interval, a phenomenon called the entanglement sudden death (ESD) [7][8][9][10][11]. The ESD is identified to be more disruptive to quantum information processing due to the fast disappearance of entanglement [7][8][9]. Under more unusual situations which require non-Markovianity of the system-environment coupling, the entanglement can reappear after its sudden death for a while, which is termed as the entanglement rebirth [9]. The entanglement sudden death and rebirth have been extensively studied theoretically [12][13][14][15][16][17][18]. On the experimental side, all-optical quantum experiments can simulate environmental couplings of photonic qubits by linear optics elements to demonstrate the ESD [19,20] as well as the non-Markovian coupling [21][22][23]. ESD is also observed between atomic ensembles but with no entanglement rebirth or non-Markovian behavior [24]. It is desirable to find an experimental system where the natural system-environment coupling and its Markovianity can be controlled to probe different kinds of en...