Experimentally freezing quantum discord in a dephasing environment using dynamical decoupling

Abstract

The discovery of the intriguing phenomenon that certain kinds of quantum correlations remain impervious to noise up to a specific point in time and then suddenly decay, has generated immense recent interest. We exploit dynamical decoupling sequences to prolong the persistence of timeinvariant quantum discord in a system of two NMR qubits decohering in independent dephasing environments. We experimentally prepare two-qubit Bell-diagonal quantum states that interact with individual dephasing channels and demonstrate the effect of dynamical decoupling on the preservation of both quantum and classical correlations. We are able to freeze quantum discord over long time scales in the presence of noise, using dynamical decoupling. We use robust state-independent dynamical decoupling schemes for state preservation and demonstrate that these schemes are able to successfully preserve quantum discord.Introduction:-The quantification of quantum correlations, distinction from their classical counterparts, and their behavior under decoherence, is of paramount importance to quantum information processing [1]. Several measures of nonclassical correlations have been developed [2] and their signatures experimentally measured on an NMR setup [3,4]. Quantum discord is a measure of nonclassical correlations that are not accounted for by quantum entanglement [5]. While the intimate connection of quantum entanglement with quantum nonlocality is well understood and entanglement has long been considered a source of quantum computational speedup [6], the importance of quantum discord, its intrinsic quantumness and its potential use in quantum information processing protocols, is being explored in a number of contemporary studies [7].

Dynamics of quantum discord of two coupled spin-1/2 subjected to time-dependent magnetic fields

“…[71] an experimental algorithm allowing the tomographic reconstruction of the density matrix of a two-qubit system has been proposed as basis to evaluate quantum discord. It is worth noticing how the diagonal Bell states, studied in this paper, play a prominent role for such kind of investigations thanks to their properties and their robustness exhibited also in open quantum systems immersed in dephasing environment [72][73][74][75].…”

Quantum discord and its allies: a review of recent progress

“…In recent years, Cianciaruso et al [649] demonstrated the freezing phenomenon of Bures distance-based GQD for a specific class of BD states, each party of which is independently interacting with a non-dissipative decohering environment. The conditions for choosing a set of initial states to freeze QD, have also been investigated for other environmental conditions [650][651][652].…”

Controlling sudden transition from classical to quantum decoherence via non-equilibrium environments

“…Furthermore, in the literature, some schemes are used to enhance the time-interval in which quantum correlations remain constant and control the appearance of sudden transition time e.g. dynamical decoupled method and non-Markovianity [24][25][26]. Unfortunately, these controlled schemes have some restrictions, for example, in the short-time interactions, the dynamical decoupling is an inappropriate technique because of the lack of memory issue [27,28].…”

“…We show for the first time that the phenomena of freezing and sudden transition still occurs even when the quantum system interacts with a nonequilibrium environment in both weak and strong coupling regimes for certain Bell diagonal states. Interestingly, unlike the application of two-flip dynamical decoupling pulse sequence technique [24][25][26], here the time interval in which the quantum correlation is unaffected by the decoherence can be further extended only by allowing the environment to deviate from equilibrium. This reflects that the non-equilibrium feature offers an efficient alternative protocol to delay the occurrence of the sudden transition time and combat against the environmental noise.…”