publications

2022

1. Il Nuovo Cimento

   Optimized state transfer in systems of ultrastrongly coupled matter and radiation

   Luigi Giannelli, Jishnu Rajendran, Nicola Macrì, Giuliano Benenti, and 3 more authors

   Il Nuovo Cimento C 45-6, 171 (2022), Mar 2022

   Abs DOI

   Ultrastrong coupling may allow faster operations for the development of quantum technologies at the expenses of increased sensitivity to new kind of intrinsic errors. We study state transfer in superconducting circuit QED architectures in the ultrastrong coupling regime. Using optimal control methods we find a protocol resilient to the main source of errors, coming from the interplay of the dynamical Casimir effect with cavity losses.

2. Il Nuovo Cimento

   Coarse-grained dynamics of ac-driven two-state systems

   Nicola Macrì, Luigi Giannelli, Jishnu Rajendran, Elisabetta Paladino, and 1 more author

   Il Nuovo Cimento C 45-6, 173 (2022), Mar 2022

   Abs DOI

   Magnus expansion is used to identify effective Hamiltonians describing the coarse-grained dynamics of more complex problems. Here, we apply this method to a two-level system driven by an and AC field. We derive Stark and Bloch-Siegert shifs of both diagonal and off-diagonal entries of the Hamiltonian as a result of coarse-graining only.

2021

1. EPJS

   Probing ultrastrong light–matter coupling in open quantum systems

   A. Ridolfo, Jishnu Rajendran, L. Giannelli, E. Paladino, and 1 more author

   The European Physical Journal Special Topics, May 2021

   Abs DOI

   Dynamically probing systems of ultrastrongly coupled light and matter by advanced coherent control have been recently proposed as a unique tool for detecting peculiar quantum features of this regime. Coherence allows in principle on-demand conversion of virtual photons dressing the entangled eigenstates of the system to real ones, with unitary efficiency and remarkable robustness. Here, we study this effect in the presence of decoherence, showing that also in far from ideal regimes is it possible to probe such peculiar features.

2019

1. IOP

   Coherent trapping in small quantum networks

   T J Pope, Jishnu Rajendran, A Ridolfo, E Paladino, and 2 more authors

   Journal of Statistical Mechanics: Theory and Experiment, Dec 2019

   Abs DOI

   We consider a three-node fully connected network (Delta network) showing that a coherent population trapping phenomenon occurs, generalizing results for the Lambda network known to support a dark state. Transport in such structures provides signatures of detrapping, which can be triggered by external controls. In the presence of an environment it turns out to be sensitive to its Markovianity. Adiabatic modulation of the system’s parameters may yield coherent population transfer, analogous to the stimulated Raman adiabatic passage phenomenon. Robustness of this protocol against non-adiabatic transitions is studied. Coherent nanostructures where these phenomena are relevant for quantum transport and quantum protocols are suggested.

2018

1. EPL

   

   Playing a true Parrondo’s game with a three-state coin on a quantum walk

   Jishnu Rajendran, and Colin Benjamin

   EPL (Europhysics Letters), Jun 2018

   Abs DOI

   Playing a Parrondo’s game with a qutrit is the subject of this paper. We show that a true quantum Parrondo’s game can be played with a 3-state coin (qutrit) in a 1D quantum walk in contrast to the fact that playing a true Parrondo’s game with a 2-state coin (qubit) in 1D quantum walk fails in the asymptotic limits.

2. RSOS

   

   Implementing Parrondo’s paradox with two-coin quantum walks

   Jishnu Rajendran, and Colin Benjamin

   Royal Society Open Science, Feb 2018

   Abs DOI

   Parrondo’s paradox is ubiquitous in games, ratchets and random walks. The apparent paradox, devised by J. M. R. Parrondo, that two losing games A and B can produce a winning outcome has been adapted in many physical and biological systems to explain their working. However, proposals on demonstrating Parrondo’s paradox using quantum walks failed for a large number of steps. In this work, we show that instead of a single coin if we consider a two-coin initial state which may or may not be entangled, we can observe a genuine Parrondo’s paradox with quantum walks. Furthermore, we focus on reasons for this and pin down the asymmetry in initial two-coin state or asymmetry in shift operator, either of which is necessary for observing a genuine Parrondo’s paradox. We extend our work to a three-coin initial state too with similar results. The implications of our work for observing quantum ratchet-like behaviour using quantum walks are also discussed.