לוח שנה משולב

Orbitofrontal cortex (OFC) has long been known to play an important role in decision making. However, the exact nature of that role has remained elusive. The OFC does not seem necessary for almost anything---animals and humans can learn, unlearn and reverse previous learning even without an OFC, albeit more slowly than their healthy counterparts. What role, then, can the OFC be playing such that its absence would cause subtle but broadly permeating deficits? We propose a new unifying theory of OFC function. Specifically, we hypothesize that OFC encodes a map of the states of the current task and their inter-relations, which provides a state space for reinforcement learning elsewhere in the brain. I will first use a simple perceptual judgement task to demonstrate that state spaces, a critical ingredient in any reinforcement learning algorithm, are learned from data. I will then use our hypothesis that the OFC encodes the learned state space to explain recent experimental findings in an odor-guided choice task (Takahashi et al, Nature Neuroscience 2012) as well as classic findings in reversal learning and extinction. Finally, I will lay out a number of testable experimental predictions that can distinguish our theory from other accounts of OFC function.

Using modern micro and nano-fabrication techniques combined with superconducting materials we realize electronic circuits the dynamics of which are governed by the laws of quantum mechanics. Making use of the strong interaction of photons with superconducting quantum two-level systems realized in these circuits we investigate both fundamental quantum effects of light and applications in quantum information processing. In this presentation, I will discuss novel methods to investigate the quantum properties of microwave frequency radiation emitted from solid state devices. Instead of employing photon counters, as commonly done at optical frequencies, we use linear amplifiers and measure the amplitude and phase of the emitted electromagnetic fields at the quantum level. For this purpose we have developed efficient methods to separate the quantum signal of interest from the noise added by the linear amplifiers [1]. To demonstrate the power of these techniques we have realized on-demand single microwave photon sources which we characterize using correlation function measurements which display anti-bunching of the detected photons [2] and full quantum state tomography which display the negativity of the extracted Wigner functions [3]. The presented techniques are readily applicable for investigating other solid state emitters in the microwave frequency domain, such as quantum dots for example. We have also explored the entanglement created between stationary emitters and freely propagating microwave photons [4] and the Hong-Ou-Mandel effect in this way.

[1] C. Eichler et al., Phys. Rev. A 86, 032106 (2012)
[2] D. Bozyigit et al., Nat. Phys. 7, 154 (2011)
[3] C. Eichler et al., Phys. Rev. Lett. 106, 220503 (2011)
[4] C. Eichler et al., Phys. Rev. Lett., in print (2012), also arXiv:1209.0441

Thirty-five years of SERS
Martin Moskovits
Department of Chemistry and Biochemistry
University of California, Santa Barbara
Scientists do not read the scientific literature. This is because, time, unlike other currencies that may be plentiful for awhile, then scarce, then plentiful again, time diminished monotonically, so that the triage one needs to make for professional success in science is simple: one either reads them, or writes them. SERS, whose inordinate enhancement was discovered by Jeanmaire and Van Duyne in 1977, has had a particularly rocky time in achieving mechanistic steady state. This is not due to the absence of a working model that was both explicative and predictive, and therefore useful in constructing new experiments. Such a model was already in place in the 1980s and supported by some excellent and sophisticated theory. (I mention the work of Metiu and Nitzan, as examples.) That model is the plasmonic model, which not only guided most of the successful experiments in SERS to date, but begat the field of Plasmonics in the bargain.
Rather, the notion that SERS lacked a sound fundamental understanding was due to an inexplicable hostility to the plasmonic model of SERS by a few prominent workers, together with a reinforcement of the rejection of the plasmonic model following the announcement of single-molecule SERS (SM-SERS), since people (forgetting that Aravind, Nitzan and Metiu in 1981 predicted a 1010 enhancement factor in the hot spot between two, almost touching silver nanoparticles) could not fathom how so great an enhancement could arise from the concentration of electromagnetic fields as to permit single-molecule Raman detection. Following the announcement of SM-SERS, and stimulated by initiatives in nanotechnology, many entered the field of SERS. The fact that most SERS experiments involve rather simple chemistry, but somewhat subtle physics, did not help. It merely granted facile entry into the field, and allowed some to generate a great deal of interesting experimental observations and publish them with only a passing understanding of the underlying mechanism.
By 1985, I believe most of us understood the way SERS worked rather well. Certainly well enough for me to have been able to state (based on the aggregate work of some two a dozen major contributors to SERS at that time) “… the majority view is that the largest contributor to the intensity amplification results from the electric field enhancement that occurs in the vicinity of small, interacting metal particles that are illuminated with light resonant or near resonant with the localized surface-plasmon frequency of the metal structure. Small in this context is gauged in relation to the wavelength of light. The special preparation required to produce the effect …is now understood to be necessary as a means for producing surfaces with appropriate
electromagnetic resonances that may couple electromagnetic fields either by generating rough films or by placing small metal particles in close proximity to one another.”
Still, even today, the mention of SERS still engenders comments such as “a phenomenon whose mechanism is not fully understood”, stated with the implication being that (unlike most other fields of science about which one can make that statement in the sense that one can always understand more) SERS is unusual in that after 35 years of work, people still apparently do random experiments wholly unguided by a successful theory. To be sure, the technology needed to nano-engineer plasmonic substrates, the computer power and the theories and codes needed to make regular nanostructures and carry out meaningful computations has improved enormously in the intervening 35 years. So that whereas 30 years ago one might have excused such a statement. Today the notion that SERS lacks a fundamental understanding is ludicrous.
Of course, the theory of SERS is incomplete since a fully quantum theory of the effect is only partially developed.
I have had the good fortune of witnessing the development of SERS from its inception. The talk will focus on some of the key people, experiments, insights and ideas, as well as some of the Quixotic individuals and notions that permeated SERS over the years, and how they led to our current understanding of SERS, and to our celebrating Chanukah at the Dwek School on Nanoplasmonics, at the Weizmann Institute in the year 5773.

Our exquisite sense of hearing has fascinated physicists for more than a century. It has been well established that hearing is an active, energy consuming, non-linear process. Major experimental progress over the last decade now allows detailed comparison between theory and experiment. The talk will review the application of dynamical systems theory to active hearing as well as experimental tests.