Scientific Series

Conventional wisdom holds that the majority of high energy atomic nuclei ("cosmic rays") that continually rain upon the Earth originate in galactic supernova shock waves, although some different (likely extragalactic) origin must be invoked to explain the highest energy particles. Despite many decades of intensive research on the subject, only indirect clues to these ideas exist at present. Direct measurements of the spectrum and mass composition of high energy cosmic rays are needed to validate these notions, but are hampered by rapidly dwindling fluxes with energy. Indeed, there is an expectation that the cosmic nuclei should have progressively more charge (and therefore mass), on average, with increasing energy, up to the astrophysical "knee" (spectral break) in the spectrum at around 3x10^15 eV. At energies beyond the knee, only indirect measurements are possible. The CREAM (Cosmic Ray Energetics And Mass) experiment is a complex particle detector flown by high altitude balloon to directly measure the charge and energy of the cosmic rays at energies near the spectral knee. It flew successfully in Antarctica in Dec 04 / Jan 05 for a record-breaking 42 days, and again in Dec 05 / Jan 06. We will review the science and performance of the instrument in flight, and present preliminary results and discuss prospects for additional CREAM missions. The Auger experiment is the largest cosmic ray detector ever built, currently nearing completion in Argentina, covering an area of 3000 km^2. Its aim is to resolve a number of mysteries surrounding the highest energy cosmic rays, beyond 10^18 eV, whose very existence and ability to reach the Earth are difficult to understand. The rarity of the highest energy particles has precluded definitive answers to the question of their nature and origin, and indeed some controversy surrounds the existing experimental evidence. The Auger experiment will afford an order of magnitude improvement in statistics over previous efforts, as well as much improved control of systematics. We will briefly review the science of the highest energy cosmic rays and present first results obtained with the growing Auger array, and discuss plans for the future of these efforts.

I argue that all necessary ingredients for successful inflation are present in the minimal supersymmetric standard model (MSSM). The potential for the supersymmetric flat directions (which can be viewed as moduli near points of enhanced symmetry) generically has metastable minima at large field values. An adjustment of soft supersymemtry breaking parameters results in a point where the first two derivatives of the potential vanish. One can then have more than 10^3 e-foldings of slow roll inflation with a Hubble rate ~ O(1-10) GeV in the vicinity of this point. The model has a robust prediction for the scalar spectral index: n_s \leq 0.93, which agrees with the current WMAP and LSS data within 2\sigma. It can be implemented purely within MSSM, or MSSM plus Dirac neutrinos. It has the unique feature of having a concrete and real connection to physics that can be observed in earthbound laboratories.

We describe a protocol for distilling maximally entangled bipartite states between random pairs of parties (``random entanglement'') from those sharing a tripartite W state, and show that this may be done at a higher rate than distillation of bipartite entanglement between specified pairs of parties (``specified entanglement''). Specifically, the optimal distillation rate for specified entanglement for the W has been previously shown to be the asymptotic entanglement of assistance of 0.92 EPR pairs per W, while our protocol can distill 1 EPR pair per W between random pairs of parties, which we conjecture to be optimal. We further extend this to a more general class of W-like states and show by increasing the number of parties in the protocol that there exist states with fixed lower-bounded distillable random entanglement for arbitrarily small specified entanglement. [Work done in collaboration with Benjamin Fortescue. Preprint available at http://arxiv.org/abs/quant-ph/0607126 ]

Quantum mechanics is a non-classical probability calculus -- but hardly the most general one imaginable. In this talk, I'll discuss some familiar non-classical properties of quantum-probabilistic models that turn out to be features of {em all} non-classical models. These include a generic no-cloning theorem obtained in recent work with Howard Barnum, Jon Barrett and Matt Leifer.

Entanglement is one of the most studied features of quantum mechanics and in particular quantum information. Yet its role in quantum information is still not clearly understood. Results such as (R. Josza and N. Linden, Proc. Roy. Soc. Lond. A 459, 2011 (2003)) show that entanglement is necessary, but stabilizer states and the Gottesman-Knill theorem (for example) imply that it is far from sufficient. I will discuss three aspects of entanglement. First, a quantum circuit with a "vanishingly small" amount of entanglement that admits an apparent exponential speed-up over the classical case. Second, I will discuss techniques for lower-bounding the amount of entanglement in bipartite quantum states. Finally, I will discuss the role of entanglement in quantum metrology. Specifically, I will show that entangling ancillas can make no difference to the accuracy of a quantum parameter estimation, regardless of the nature of the coupling Hamiltonian. I will conclude by discussing strategies for improving the scaling of quantum parameter estimation.

Traditional quantum state tomography requires a number of measurements that grows exponentially with the number of qubits n. But using ideas from computational learning theory, I'll show that "for most practical purposes" one can learn a quantum state using a number of measurements that grows only linearly with n. I'll discuss applications of this result in experimental physics and quantum computing theory, as well as possible implications for the foundations of quantum mechanics. quant-ph/0608142

I will demonstrate how one can realize Cascade inflation in M-theory. Cascade inflation is a realization of assisted inflation which is driven by non-perturbative interactions of N M5-branes. Its power spectrum possesses three distinctive signatures: a decisive power suppression at small scales, oscillations around the scales that cross the horizon when the inflaton potential jumps and stepwise decrease in the scalar spectral index. All three properties result from features in the inflaton potential. The features in the inflaton potential are generated whenever two M5-branes collide with the boundaries. The derived small-scale power suppression serves as a possible explanation for the dearth of observed dwarf galaxies in the Milky Way halo. The oscillations, furthermore, allow to directly probe M-theory by measurements of the spectral index and to distinguish cascade inflation observationally from other string inflation models.

My field is the foundations of quantum mechanics, in particular Bohmian mechanics, a non-relativistic theory that is empirically equivalent to standard quantum mechanics while solving all of its paradoxes in an elegant and simple way, essentially by assuming that particles have trajectories. Bohmian mechanics possesses a straightforward generalization to relativistic space-time, be it flat or curved, if one assumption against the spirit of relativity is granted: the existence of a "time foliation", i.e., a physical object mathematically represented by a slicing of space-time into spacelike 3-surfaces, which evolves according to a Lorentz-invariant law. On the basis of this kind of theory, describing particles in a background 4-geometry, I propose an extension in which the space-time geometry is dynamically generated, as in general relativity. Whether my model is empirically equivalent to any known type of quantum gravity I don't know. In this model, there is a Lorentzian metric on configuration-space-time, evolving according to the higher-dimensional analog of the Einstein field equation. The 4-metric is obtained from the configuration-space-time metric and the actual particle configuration. Thus, this Bohm-like model generates (up to diffeomorphisms) a 4-metric and particle world lines from a given wave function.