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Curriculum Vitae
A reasonably recent version of my CV can be downloaded here.
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Dr Kheruntsyan is recognised internationally as one of the pioneers of theoretical quantum-atom optics within the field of ultracold gases. He has made a number of significant contributions to the field, which have led to important experiments in leading laboratories worldwide and influenced subsequent trends in theory, such as the theory of resonant superfluidity and the theory of atom correlations in low-dimensional quantum gases. The most significant contributions are in the following areas:
1. FORMATION OF MOLECULAR BOSE-EINSTEIN CONDENSATES.
Density of coherently coupled atomic (top) and molecular (bottom) Bose-Einstein condensates as a function of time. The out-of-phase oscillations correspond to intercorverison between the respective BECs.
In 1998 Kheruntsyan (with Drummond and He) introduced a field-theoretic model for the description of coherently coupled atomic and molecular Bose-Einstein condensates (BECs) [Phys. Rev. Lett. 81, 3055 (1998)]. The work was subsequently extended to describe a new mechanism for the formation of a molecular BEC using coherent Raman photoassociation of an atomic BEC [Phys. Rev. Lett. 84, 5029 (2000)]. Previous descriptions of the formation of (e.g., diatomic) molecules were based on rate equations and the underlying two-body atom-atom interactions. In contrast to this, Kheruntsyan’s work predicted the possibility of coherent, matter-wave interactions in which the atoms and molecules couple as entire condensates. This implies a non-Arrhenius chemical kinetics or “superchemistry” [Phys. Rev. Lett. 84, 5029 (2000)], in which the chemical reaction rates are Bose-enhanced rather than suppressed as the temperature is reduced.
Subsequent developments of these pioneering ideas and extensions of the theoretical model to include fermionic atoms [K. V. Kheruntsyan and P. D. Drummond, Phys. Rev. A 61, 063816 (2000); together with an independent work by M. Holland et al., Phys. Rev. Lett. 87, 120406 (2001) and E. Timmermans et al., Phys. Phys. Lett. A 285, 228 (2001)] have led to the theory of resonant superfluidity with magnetically tunable Feshbach resonance molecules (the so-called “two-channel model”) and to the production of molecular BECs from atomic BECs in more than 10 laboratories worldwide. The discovery of Feshbach resonance molecules has in turn led to significant new insights in the understanding of the physics of the BEC-BCS crossover studied previously in condensed matter systems in the context of superconductivity. This was one of the early examples of new interdisciplinary links of cold atom physics with other sub-fields of physics. The following quote from page 72 of the 2007 Report of the Committee on Atomic, Molecular, and Optical Physics of the US National Academies (The National Academies Press, Washington, 2007) is an indirect reference to Kheruntsyan’s contribution:
While experimental breakthroughs constantly challenge theorists, the reverse is also true, with theorists suggesting new experimental paths and novel ways to reach exciting regimes where new physics can be explored. For example, the possibility of using Feshbach resonances to achieve new regimes of ultracold physics was suggested by theorists. This proposal led to the creation of molecular condensates and opened the way to one of the most exciting recent discoveries in AMO physics: observation of the crossover between Bose condensation and Cooper pairing of fermions. As a result, there is a new link between atomic and condensed matter physics.
Kheruntsyan’s subsequent work [P. D. Drummond and K. V. Kheruntsyan, Phys. Rev. A 70, 033609 (2004)] applied their theoretical predictions to the experimentally measured binding energies of 85Rb2 and 40K2 Feshbach resonance molecules, and found excellent agreement between the theory and experiment.
2. ATOM-ATOM CORRELATIONS AND THERMODYNAMICS OF 1D BOSE GASES.
In 2003, Kheruntsyan (with Gangardt, Drummond, and Shlyapnikov) produced the world-first exact calculation of atom-atom pair correlations in a 1D Bose gas [Phys. Rev. Lett. 91, 040403 (2003)]. The 1D Bose gas is of fundamental importance to quantum many-body physics as the underlying model is exactly integrable. First theoretical treatments of the 1D Bose gas problem go back to 1963 (when Lieb and Liniger found the exact many-body wave-function for the model) and 1969 (when the Nobel Laureate C.N.Yang and his brother C.P.Yang solved the model for the finite temperature thermodynamics). These exact solutions remained a tour-de-force of mathematical physics for more than 40 years, until Kheruntsyan, Gangardt, Drummond and Shlyapnikov calculated the atom-atom correlation functions at arbitrary interaction strengths and temperatures for an experimentally realistic system of an ultracold atomic gas confined in a highly-anisotropic (cigar-shaped) trap. Kheruntsyan and co-workers have been able for the first time to map out the complete phase diagram of the system and to discover two new regimes of quantum degeneracy – the decoherent quantum regime and the regime of high-temperature fermionisation [Phys. Rev. A 71, 053615 (2005)]. Kheruntsyan and the team proposed simple correlation measurements that could test their theoretical predictions experimentally. These predictions were confirmed in 2004 in the W. Phillips at NIST, and in 2005 in the D. Weiss’s group at Pennsylvania State University.
In 2008, Kheruntsyan and the experimental group of N. J. van Druten (University of Amsterdam) published another highly cited paper on the thermodynamic properties of a 1D Bose gas created on an atom chip [Phys. Rev. Lett. 100, 090402 (2008)]. The team has succeeded in comparing the temperature and atom number density of the 1D quantum gas to the exact thermodynamics developed by Yang and Yang back in 1969. Kheruntsyan’s role in this theory-experiment collaboration was the theoretical calculation of the experimentally observed density profiles, which gave crucial insights into the interpretation of the experimental data, not available by any other existing theoretical approaches.
Understanding of the physics of 1D Bose gases and atom-atom correlations developed by Kheruntsyan is an important step towards the design of atomic waveguides and atom interferometers operating in low-dimensional environments, since the strength of these correlations determine the ultimate operating limits of such devices.
Media releases:
3. GENERATION OF EINSTEIN-PODOLSKY-ROSEN ENTANGLEMENT AND CORRELATED ATOM LASER BEAMS VIA MOLECULAR DISSOCIATION.
Pair correlated or 'twin' atom-laser beams resulting from a quantum dynamical simulation of the process of coherent dissociation of a BEC of molecular dimers [Phys. Rev. A 66, 031602(R) (2002)].
This pioneering theoretical proposal [Phys. Rev. Lett. 95, 150405 (2005)] is the atom optics analog of parametric down-conversion with photons. The latter process was pivotal in the advancement of quantum optics and provided the most reliable sources of pair-correlated photons that were used in the optical demonstrations of the famous Einstein-Podolsky-Rosen paradox. By proposing the matter-wave analog of this process, using dissociation of a Bose-Einstein condensate of diatomic molecules made of bosonic (integer spin) atoms, Kheruntsyan, Olsen, and Drummond have shown – for the first time – how one could generate EPR-entangled states with ultracold atoms in a 1D trap and how one should detect this entanglement using mode-matched atomic quadratures.
One of the referees of Kheruntsyan’s paper made the following remarks in their report: “... rather trivial statements about pair correlations in cold atoms are sometimes made, but in this case the authors have gone further and added enough substance to make a difference.” Indeed, Kheruntsyan and co-worker’s contribution was the proposal to use mode-matched ‘local oscillator’ fields which gave precise, operationally defined criteria for detecting EPR-entanglement between correlated mater waves.
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4. FERMIONIC QUANTUM-ATOM OPTICS.
This is the first theoretical model of dissociation of a molecular Bose-Einstein condensate into correlated fermionic atoms [Phys. Rev. Lett. 96, 110401 (2006)], which represents the fermionic analog of optical parametric down-conversion. The work outlines a new paradigm of fermionic quantum-atom optics and extends the field of quantum-atom optics from bosonic (integer spin) to fermionic (half-integer spin) atoms. Indeed, while quantum-atom optics was initially established as a natural extension of ideas from quantum optics with photons (which are also bosons), a direct application of these ideas to fermionic atoms had an intriguing twist: the underlying quantum statistics were different. As a result, the analogies with quantum optics and the implications for possible future applications were less straightforward. Kheruntsyan’s work showed how to create correlated states of fermionic atoms with suppressed (‘squeezed’) relative number fluctuations. Pair-correlated atoms have been produced and detected in Jin’s laboratory at JILA (Boulder, USA) using dissociation of a BEC of potassium molecules, in agreement with Kheruntsyan’s predictions.
Possible applications of squeezed states of ultracold atomic gases lie in the design of atom interferometers for precision measurements and new fundamental tests of quantum theory.
5. FIRST-PRINCIPLE SIMULATIONS OF QUANTUM MANY-BODY DYNAMICS.
Kheruntsyan is an internationally recognised expert in phase-space methods for simulating exact many-body dynamics of interacting BECs. He was the first to perform ab initio simulations of dissociation of molecular BECs [Phys. Rev. A 66, 031602(R) (2002); Phys. Rev. A 74, 033620 (2006)] and to model the experiments on collisions of metastable helium condensates using the positive-P representation [New J. Phys. 10, 045021 (2008)].
The condensate collision simulations performed by Kheruntsyan in Ref. [New J. Phys. 10, 045021 (2008)] involved N=105 helium atoms and M=4200x40x40=6,720,000 momentum modes, which corresponds to a Hilbert space of dimension D=MN≈10700,000. This is one of the largest Hilbert spaces ever treated in an exact quantum dynamical simulation and represents a tour-de-force of computational physics.
The results of these simulations are in excellent agreement with the experiments in C. Westbrook’s group and explain many of the observed phenomena (see, e.g., Phys. Rev. Lett. 104, 150402 (2010); Phys. Rev. Lett. 105, 190402 (2010)), in contrast to the previously used approximate theoretical approaches.
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