Events - Weekly
|Sunday, March 9|
|Monday, March 10|
Biophysics Seminar Series - Daniel Kronauer (Rockefeller)
"The clonal raider ant Cerapachys biroi as a new model system for social evolution and behavior"
Joseph Henry Room · 12:00 p.m.– 1:00 p.m.
Condensed Matter Seminar, Christian Schoenenberger, "Cooper-Pair Splitting and Spectroscopy in Double Quantum Dot Devices with Superconducting Charge
An elegant idea for the creation of entangled electrons in a solid-state device is to split Cooper pairs, which are in a spin singlet state, by coupling a superconductor to two parallel quantum dots (QDs) in a Y-junction geometry . Cooper pair splitting (CPS) was investigated recently in devices based on InAs nanowires [2,3] and carbon nanotubes (CNTs) [4,5] and identified by a positive correlation between the currents through the QDs. I will first discuss recent experiments that demonstrate high splitting efficiencies > 90%. A high CPS efficiency is a prerequisite for Bell state measurements, a clear way of proving that Cooper pairs can be extracted coherently and lead to spatially separated entangled electron pairs. Further requirements on entanglement measurements will be addressed in the talk as well. I will then continue to discuss new results in semiconducting nanowires with Nb contacts that display a great variety of correlations. Using also Nb as the injector another distinct experiment with CNT devices will be discussed. In the regime of a strong tunnel coupling between the QDs and superconducting contact, the CPS efficiency is expected to be small . However, the superconducting proximity effect can support so-called Andreev bound states (ABS) on a QD, which can be detected by conventional transport spectroscopy . Here we use a Niobium contacted CNT Cooper pair splitter and investigate the response of the ABS formed on one QD to CPS. We find an appreciable non-local conductance when the bias is large enough to excite charge fluctuations in the ABS. These non-local signals change sign with opposite bias and, more intriguingly, when the ABS ground state changes from a spin singlet to a doublet. Our experiments can be understood qualitatively in an intuitive picture for ABS and CPS and show that CPS can be used as a tool to investigate complex hybrid nanoelectronic structures.
This is a collaborative effort with the groups of Szabolcs Csonka, Budapst University of Technology and Economy, Jesper Nygard, Nano-Science Center, Niels Bohr Institute of the University of Copenhagen, and Jan Martinek- IFM-PAN, Poznan, Polen. I acknowledge funding from the Swiss NFS, SNI , NCCR-QSIT, FP7-SE2ND and ERC-QUEST.
 P. Recher, E.V. Sukhorukov and D. Loss, Phys. Rev. B 63, 165314 (2001).
 L. Hofstetter, S. Csonka, J. Nygård and C. Schönenberger, Nature 461, 960 (2009).
 L. Hofstetter, S. Csonka, A. Baumgartner, G. Fülöp S. d’Hollosy, J. Nygård and C. Schönenberger, Phys. Rev. Lett. 107, 136801 (2011).
 L.G. Herrmann, F. Portier, P. Roche, A. Levy Yeyati, T. Kontos and C. Strunk, Phys. Rev. Lett. 104, 026801 (2010).
 J. Schindele, A. Baumgartner, and C. Schönenberger, Phys. Rev. Lett. 109, 157002 (2012).
 J.-D. Pillet, C.H.L. Quay, P. Morfin, C. Bena, A. Levy Yeyati and P. Joyez, Nature Phys. 6, 965 (2010).
Jadwin A10 · 1:15 p.m.– 2:30 p.m.
PCTS Seminar - Michael E. Peskin SLAC National Accelerator Laboratory, Stanford University - “Composite Higgs and Naturalness”
PCTS Seminar Room · 2:30 p.m.– 3:30 p.m.
|Tuesday, March 11|
Quantum Sciences Seminar Series - Jérémie Viennot, ENS Paris, "Out of equilibrium charge dynamics in a cQED architecture"
In the context of circuit quantum electrodynamics, recent developments made it possible to build hybrid circuits , including many types of quantum dots. The versatility of these systems allows us to explore several directions, from quantum information engineering to many-body physics, all in a circuit QED architecture. I will present some of the experiments of our group where a carbon nanotube-based double quantum dot is coupled to a microwave cavity.
Using a novel carbon nanotube stamping technique , we demonstrate a strong electron confinement, allowing us to bring the system at resonance with the cavity and use it as a charge qubit. We characterise the response of this circuit out of equilibrium, driving the system either with a finite bias or with a microwave spectroscopic tone .
Combined with exchange Zeeman fields induced by ferromagnetic interfaces, such a control should enable us to go towards spin-photon coupling and spin qubit experiments for circuit QED . I will discuss some preliminary results pointing towards spin-photon coupling signatures in such an architecture.
 M.R. Delbecq et al. Nature Comm., 4, 1400 (2013).
 J.J. Viennot et al., submitted.
 J.J. Viennot et al., arXiv:1310.4363.
 A. Cottet et al., Phys. Rev. Lett. 105, 160502 (2010).
Jadwin 111 · 1:00 p.m.– 2:00 p.m.
Special Cosmology Seminar, Nico Yunes "I-Love-Q"
Neutron stars and quark stars are not only characterized by their mass and radius, but also by how fast they spin, through their moment of inertia, and how much they can be deformed, through their Love number and quadrupole moment. These depend sensitively on the star's internal structure, and thus on unknown nuclear physics. In spite of this, we have found quasi-universal (I-Love-Q) relations between the moment of inertia, the Love number and the quadrupole moment that are independent of the neutron star's and quark star's internal structure.
We have used these as a basis of a no-hair-like theorem for neutron stars that bares strong similarities with the well-known black hole no-hair theorems. These relations can be used to learn about neutron star deformability through observations of the moment of inertia, break degeneracies in gravitational wave detection to measure spin in binary inspirals, and test General Relativity in a nuclear-structure independent fashion.
Joseph Henry Room · 2:00 p.m.– 3:00 p.m.
|Wednesday, March 12|
Special Seminar - Physical forces shaping morphology - Karen Alim, Harvard
Physical forces can induce long-ranged interactions and thus propagate information on large scales. Especially during the development of an organism, coordination on large scales in short time is essential. My aim is to discover the principal mechanisms of how physical forces induce, transmit and respond to biological signals and thus orchestrate development and shape morphology.
The network-forming slime mold Physarum polycephalum lacks any central coordination center, yet it shows often-termed intelligent dynamics in the way it grows and adapts its network morphology. My work investigates the role of fluid mechanics for transport and signal transfer during the morphological dynamics of this network-like slime mold. I combine experimental observations of the fluid flow and its driving force with the development of the theoretical concept of transport by peristaltic flow in a network. This synergy allows me to show that the slime mold actively controls its internal fluid flow by establishing a peristaltic wave. This peristaltic wave always spans the total extent of an individual independent of its size. Thus, I find that the slime mold actively adapts its flows as to maximize transport. The quantitative description of flows in P. polycephalum enables a new view on the slime molds growth dynamics during the encounter of food or toxins and how their location can be “remembered”, an important step to perform an informed decision during an individuals network growth and adaptation.
Jadwin A06 · 2:00 p.m.– 3:00 p.m.
|Thursday, March 13|
|Friday, March 14|
Special seminar - Fereshte Ghahari, Columbia University, "Transport and Thermoelectric Studies of Correlated Phenomena in Graphene"
The observation of correlated electron physics in graphene is mostly limited by strong electron scattering that is caused by charge impurities. We fabricate devices in which electrically contacted and electrostatically gated graphene flakes are either suspended over a SiO2 substrate or deposited on a hexagonal boron nitride layer such that a drastic suppression of disorder is achieved. The mobility of our graphene flakes exceeds 100,000 cm2/Vs. This very high mobility allows us to observe previously inaccessible transport regimes. In particular, we succeeded to observe the fractional quantum Hall Effect for the first time, hereby supporting the existence of interaction induced correlated electron states in the presence of a magnetic field. We were able to measure the energy gap associated with the fractional ν=1/3 state. This gap is at least 3 times larger than that of the 2DEGs in the best quality GaAs heterojunctions in a similar field range.
In addition, at low carrier density graphene becomes an insulator with an energy gap tunable by a magnetic field. The insulating behavior at the charge neutrality point is independent of the in plane magnetic field indicating that the ν=0 quantum hall state in graphene is not spin polarized. Apart from that, we probed the e-e correlations in graphene by means of thermopower measurements. Our results show that at high temperatures the measured thermopower deviates from the generally accepted Mott's formula and that this deviation increases for samples with higher mobility. We quantify this deviation in both the degenerate and the non-degenerate regime using Boltzmann transport theory. We consider different scattering mechanisms in the system including electron-electron scattering.
Jadwin A06 · 1:30 p.m.– 2:30 p.m.
|Saturday, March 15|