Associative pattern recognition by materials

`Software' neural networks can recognize subtle associations and patterns in complex data. Can we have similar pattern recognition in 'hardware'? Indeed, our work on origami and molecular self-assembly has shown that these systems can recall a stored `memory' by 'association' from an imprecise external signal.

As a result, we find a golden window in which systems can be multi-functional and are yet as easy to control as dedicated single-purpose devices.  We are exploring implications for new kinds kinetic architecture, protein complexes and fun new toys!

Publications:
1. Murugan, Zeravcic, Leibler and Brenner   PNAS 112(1) 54-59 (Dec 2014)
and manuscripts in preparation.

Exploration and error correction using non-equilibrium dynamics

Biochemical reactions use non-equilibrium driving forces to correct errors, search effectively, perform statistical inference and to regulate and time processes precisely. Such mechanisms are at the fascinating intersection of non-equilibrium physics and algorithms since these physical systems seem to solve problems you would normally understand through algorithms.  Can one design better non-equilibrium mechanisms based on algorithmic ideas?

Publications:
1. Murugan, Huse, Leibler, PNAS 109(30):12034-9 (2012)
2. Murugan, Huse, Leibler, Physical Review X 4 (2), 021016 
3. Murugan, Vaikuntanatan. Journal of Stat. Phys. 2016, 162 (5)
4. Murugan, Vaikuntanatan (in preparation)

Recognition, discrimination and olfaction
Information theory of shape

How many distinct lock-key pairs can you make before you run out of shapes and some keys inevitably open the wrong locks (crosstalk)? If you could only ask 20 questions about a shape to figure out its identity, what aspects of shape would you ask about?

 Such abstract questions underlie the optimal design of receptor libraries for natural and synthetic olfaction, self-assembly of complex structures, minimizing crosstalk in signal transduction and other such problems of recognition in collectives. In addition to biochemical specificity, we are developing a coding and information theory of `shape' itself.

Publications: 
1. Capacity of specific glues, w/ Huntley, Brenner (PNAS May 2016)
2. Natural statistics and optimal library design for olfaction, w/ Zwicker, Brenner, (PNAS, April 2016)

---

Past work

Entanglement and confinement

 Quantum entanglement has been a fruitful idea in many areas of physics but until recently, without much use in particle physics. We proposed entanglement between quarks as a subtle test of whether quarks are inseparably bound ("confined") in any given theory of quarks and gluons. Our proposal was validated by lattice simulations by groups at Argonne National Labs/U Chicago and ITEP (Moscow). Entanglement entropy has since found many other applications in particle physics and string theory and has become a popular area of research in recent years.

Publications: 
Entanglement as a probe of Confinement, 
with David Kutasov and Igor Klebanov, Nuclear Physics B (796), 274 (2008)

Gauge-gravity duality 
Geometric solutions to difficult problems in inflationary cosmology and renormalization group theory

The AdS/CFT correspondence shows how problems in particle physics can be mathematically translated to geometric problems in Einstein’s theory of gravity in higher dimensional spacetimes. We used this correspondence to show how difficult calculations in models of inflationary cosmology could be solved easily using the geometric interpretation.  For example, it is difficult to derive predictions from some models of inflationary cosmology due to strongly interacting quantum fields present in such models. We showed that this problem was equivalent to a simpler system of gravitational interactions a particle and a membrane in curved spacetimes. 
We also studied other strongly interacting behavior in quantum field theories (renormalization group flows, conformal field theory) using geometric problems in gravity through the AdS/CFT correspondence. 

Publications: 
On D3-brane potentials in compactifications with fluxes and wrapped D-branes,  
with D. Baumann, A. Dymarsky, I. R. Klebanov, J. M. Maldacena and L. P. McAllister   PDF
Gauge/Gravity Duality and Warped Resolved Conifold, with I. R. Klebanov      PDF
AdS4/CFT3 - squashed, stretched and warped,  with: I.R.Klebanov and T.Klose  PDF
Goldstone Bosons and Global Strings in a Warped Resolved Conifold, 
with I. R. Klebanov, D. Rodriguez-Gomez and J. Ward                                                      PDF
Fatgraph expansion for noncritical superstrings, with A. Kapustin                     PDF

---