Unfortunately, seminars are cancelled for the remainder of the semester until further notice, due to COVID-19.
NEWS: The CQM Distinguished Lecture series has been established in the Fall of 2015 to bring to Stony Brook University the renown experts in the physics of quantum matter.
February – May 2020
“Exploring Quantum Materials with Atomic Qubit Sensor”
We are witnessing a revolution in which quantum phenomena are being harnessed for next-generation technology. In this context, atomic qubits associated with defects in solids, such as nitrogen-vacancy (NV) centers in diamond, provide versatile building blocks for quantum technologies due to their optical addressability, atomic size, and excellent coherence. Among the applications being explored with such platform, quantum sensing technology realized with NV centers has emerged as a powerful probe of quantum materials. Due to its ability to sense magnetic field with high spatial resolution over wide temperature and dynamic range, NV sensors enable the exploration of condensed matter phenomena in parameter space inaccessible to existing probes. In this talk, I will discuss our application of NV quantum sensing technology to study correlated electronic and spin phenomena. We have directly imaged, for the first time, the viscous Poiseuille flow of the Dirac fluid in neutral graphene, a finding that holds implications for other strongly correlated electrons such as those in high-Tc superconductors. Enabled by the NV platform, we have developed new capabilities for probing coherent spin-waves, which can be applied to study novel magnetic materials and spintronic devices, and a technique for characterizing low-dimensional high-Tc cuprates without electrical contacts. Looking forward, I will highlight opportunities for advancing the frontiers of quantum materials and quantum technology enabled by NVs and other solid-state atomic qubits.
Non-volatile quantized states are ideal for the realization of classical Boolean logics. Abrikosov vortex represents the most compact magnetic object in superconductors with the size determined by the London penetration depth ~100 nm. Therefore, it can be utilized for creation of high-density digital cryoelectronics. In this talk we will describe operation of memory cells, in which a single vortex is used as an information bit . The vortex is pinned at a nano-scale trap and is read-out by a nearby Josephson junction [2,3]. Unlike SQUID-based memory cells, such cells have non-degenerate 0 and 1 states, which greatly simplify the device architecture. Furthermore, SQUID-based devices have a problem with increasing write current upon decreasing the SQUID loop size, preventing a straightforward miniaturization. To the contrary, write current for a vortex is determined by the depinning current density and, therefore, scales with the size. All together this allows simple miniaturization down to sub-micron sizes. We demonstrate that vortex memory cells have a high-endurance operation, are characterized by an infinite magnetoresistance, do not require external magnetic field, have a short access time, and a low write energy. Non-volatility and perfect reproducibility are inherent for such devices due to the quantized nature of the vortex. We argue that vortex-based memory can be used in superconducting digital supercomputers.
 T. Golod, A. Iovan, and V. M. Krasnov, Nat. Commun. 6, 8628 (2015).
 T. Golod, A. Rydh, and V. M. Krasnov, Phys. Rev. Lett. 104, 227003 (2010).
 T. Golod, A. Pagliero, and V. M. Krasnov, Phys. Rev. B 100, 174511 (2019).
Acknowledgements: The work was done in collaboration with Taras Golod, Adrian Iovan, Alessandro Pagliero, Olena Kapran and Lise Morlet-Decarnin. The work was supported by the European Union H2020-WIDESPREAD-05-2017-Twinning project SPINTECH under Grant Agreement No. 810144.
Vladimir Krasnov has graduated from Moscow Institute of Physics and Technology in 1990. He completed his PhD in 1995 from the Institute of Solid State Physics, Chernogolovka, Russia and postdoctoral studies from Danish Technical University and Chalmers University of Technology, Sweden. Since 2005 he is professor and head of the Experimental Condensed Matter Physics group at the Department of Physics, Stockholm University.
Supersymmetry method for interacting chaotic and disordered systems: the SYK model
The supersymmetry method was originally developed for studies of quantum phenomena in non-interacting disordered and chaotic systems.
I will report a step forward in this direction and develop the supersymmetry method for the Sachdev-Ye-Kitaev (SYK) model and other similar 0+1 dimensional interacting systems with disorder, where analytical techniques for quenched averaging have so far been based on the replica trick. As a demonstration of how the supersymmetry method works for such interacting systems, I will derive saddle point equations. In the semiclassical limit, the results are in agreement with those found using the replica technique. I will also discuss the formally exact superbosonized representation of the SYK model and argue that it paves the way for the precise calculation of the window of universality in which random matrix theory is applicable to the chaotic SYK system.
This Seminar has been cancelled due to COVID-19.
title: Novel optical probe scanning method
Host: Sasha Abanov
Host: Sasha Abanov