As I get ready to head to Germany for my first ever experience lecturing at a Max Planck summer school, I wanted to point out very briefly three of a number of interesting papers that came through the arxiv this week.
arxiv:1105.4055 - Janssen et al., Graphene, universality of the quantum Hall effect and re-definition of the SI
This paper compares the quantization of the Hall resistance in two different two-dimensional electronic systems: a conventional 2d electron gas in a GaAs/AlGaAs structure, and graphene. The authors find that the Hall resistance is quantized in units of h/e2 identically in the two systems to parts in 1011. On the one hand, this is really amazing, since you're seeing essentially exact quantization in two different systems, and the whole basis for the quantum Hall effect relies in part on dirt - without disorder, you wouldn't see the quantum Hall physics. And yet, even though the materials differ and dirt plays an important role, you get precise quantization in terms of fundamental constants. This is the kind of emergent, exact phenomenon that shows the profound character of condensed matter physics.
arxiv:1105.4642 - Barends et al., Loss and decoherence due to stray infrared light in superconducting quantum circuits
As someone who struggled mightily in grad school to avoid the effects of infinitesimal amounts of rf noise leaking into his ultracold sample, this impressed me. The authors demonstrate that infrared radiation from the surroundings, even when those surroundings are at 4.2 K, can have marked, detectable impact on the coherence properties of superconducting quantum bits. They compare results with and without an absorbing radiation shield in the way, and the effects aren't small. Wild. Time to break out those 50 mK shields from our old nuclear demag cryostat....
arxiv:1105.4652 - Paik et al., How coherent are Josephson junctions?
Along these same lines, these authors have been able to demonstrate coherence times in superconducting qubits that stretching into the tens of microseconds scale. They do this via a new kind of cavity, essentially controlling the environmental dissipation. This isn't really my area, but I know enough to be impressed, and also to be surprised at the apparent lack of the usually ubiquitous 1/f noise problems (in the critical current) that often limit coherence in these kinds of devices. As they point out, these numbers are encouragingly close to the thresholds needed for quantum error correction to be realistic.