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Nevou L, Liverini V, Friedli P, Castellano F, Bismuto A, Sigg H, et al. Current quantization in an optically driven electron pump based on self-assembled quantum dots. Nat Phys. 2011;7:423–427.
Abstract: The electronic structure of self-assembled semiconductor quantum dots consists of discrete atom-like states that can be populated with a well-defined number of electrons. This property can be used to fabricate a d.c. current standard that enables the unit of ampere to be independently defined. Here we report an optically pumped current source based on self-assembled InAs/GaAs quantum dots. The accuracy obtained so far is 10–1 and is limited by the uncertainty in the number of dots. At 10 K the device generates a current difference of 2.39 nA at a frequency of 1 kHz. The accuracy could be improved by site-selective growth techniques where the number of dots is fixed by pre-patterning. The results are promising for applications in electrical metrology, where a current standard is needed to close the so-called quantum metrological triangle.
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Ma X-S, Dakic B, Naylor W, Zeilinger A, Walther P. Quantum simulation of the wavefunction to probe frustrated Heisenberg spin systems. Nat Phys. 2011;7(5):399–405.
Abstract: Quantum simulators are controllable quantum systems that can reproduce the dynamics of the system of interest in situations that are not amenable to classical computers. Recent developments in quantum technology enable the precise control of individual quantum particles as required for studying complex quantum systems. In particular, quantum simulators capable of simulating frustrated Heisenberg spin systems provide platforms for understanding exotic matter such as high-temperature superconductors. Here we report the analogue quantum simulation of the ground-state wavefunction to probe arbitrary Heisenberg-type interactions among four spin-1/2 particles. Depending on the interaction strength, frustration within the system emerges such that the ground state evolves from a localized to a resonating-valence-bond state. This spin-1/2 tetramer is created using the polarization states of four photons. The single-particle addressability and tunable measurement-induced interactions provide us with insights into entanglement dynamics among individual particles. We directly extract ground-state energies and pairwise quantum correlations to observe the monogamy of entanglement.
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Gao J, McMillan JF, Wong CW. Nanophotonics: Remote on-chip coupling. Nat Photon. 2012;6(1):7–8.
Abstract: Scientists have demonstrated strongly coupled photon states between two distant high-Q photonic crystal cavities connected by a photonic crystal waveguide. Remote dynamic control over the coupled states could aid the development of delay lines, optical buffers and qubit operations in both classical and quantum information processing.
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Pile D. How many bits can a photon carry. Nat Photon. 2012;6(1):14–5.
Abstract: Quantum physics offers a way to enhance the amount of information a photon can carry, with potential applications in optical communication, lithography, metrology and imaging.
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Santori C, Beausoleil RG. Quantum memory: Phonons in diamond crystals. Nat Photon. 2012;6:10–2.
Abstract: The demonstration that quantum information can be stored in a bulk-diamond crystal in the form of an optically excited phonon gives researchers a new type of mechanical solid-state quantum memory to explore.
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