Tuesdays 10:30 - 11:30 | Fridays 11:30 - 12:30
Showing votes from 2017-01-10 11:30 to 2017-01-13 12:30 | Next meeting is Friday May 22nd, 11:30 am.
We review the status of the theory of dRGT massive gravity, and some of its extensions, as applied to cosmology and the cosmological constant problem.
The photon mass, $m_\gamma$, can in principle be constrained using measurements of the dispersion measures (DMs) of fast radio bursts (FRBs), once the FRB redshifts are known. The DM of the repeating FRB 121102 is known to $< 1$\%, a host galaxy has now been identified with high confidence,and its redshift, $z$, has now been determined with high accuracy: $z = 0.19273(8)$. Taking into account the plasma contributions to the DM from the Intergalactic medium (IGM) and the Milky Way, we use the data on FRB 121102 to derive the constraint $m_\gamma \lesssim 2.2 \times 10^{-14}$ eV c$^{-2}$ ($3.9 \times 10^{-50}$ kg). Since the plasma and photon mass contributions to DMs have different redshift dependences, they could in principle be distinguished by measurements of more FRB redshifts, enabling the sensitivity to $m_\gamma$ to be improved.
The notion of compressed quantum computation is employed to simulate the Ising interaction of a 1D--chain consisting out of $n$ qubits using the universal IBM cloud quantum computer running on $\log(n)$ qubits. The external field parameter that controls the quantum phase transition of this model translates into particular settings of the quantum gates that generate the circuit. We measure the magnetization, which displays the quantum phase transition, on a two--qubit system, which simulates a four--qubit Ising chain, and show its agreement with the theoretical prediction within a certain error. We also discuss the relevant point of how to assess errors when using a cloud quantum computer. As a solution, we propose to use validating circuits, that is to run independent controlled quantum circuits of similar complexity to the circuit of interest.