Localization effects induced by decoherence in superpositions of many-spin quantum states

Abstract

The spurious interaction of quantum systems with their environment known as decoherence leads, as a function of time, to a decay of coherence of superposition states. Since the interactions between system and environment are local, they can also cause a loss of spatial coherence: correlations between spatially distant parts of the system are lost and the equilibrium states can become localized. This effect limits the distance over which quantum information can be transmitted, e.g., along a spin chain. We investigate this issue in a nuclear magnetic resonance quantum simulator, where it is possible to monitor the spreading of quantum information in a three-dimensional network: states that are initially localized on individual spins (qubits) spread under the influence of a suitable Hamiltonian apparently without limits. If we add a perturbation to this Hamiltonian, the spreading stops and the system reaches a limiting size, which becomes smaller as the strength of the perturbation increases. This limiting size appears to represent a dynamical equilibrium. We present a phenomenological model to describe these results.

Quantum simulations of localization effects with dipolar interactions

“…Whereas disorder induced inhibition of transport of non interacting waves has been studied in various physical systems [41][42][43][44][45], the role of dipolar interactions is under theoretical investigation [46]. Here we study a 3D spin-network and demonstrated experimentally a similar behavior by studying the localization effects induced by the finite precision of quantum gate operations used for transferring quantum states [35,36].…”

“…Based on our previous results and methods developed in Refs. [35,36], we prepared a system of nuclear spins 1/2. Starting with uncorrelated spins we let them evolve into clusters of correlated spins with increasing size.…”

Robust dynamical decoupling

“…One contribution of 14 to a Theme Issue 'Quantum information processing in NMR: theory and experiment '. This journal is © 2012 The Royal Society which one can transfer information or analogously limits the number of qubits that one can control reliably [19,20]. This is manifested as a localization effect for the quantum information [19][20][21][22][23][24][25][26][27].…”

“…This is manifested as a localization effect for the quantum information [19][20][21][22][23][24][25][26][27]. In order to overcome these limitations and implement quantum information processing (QIP) with large numbers of qubits, methods for reducing decoherence have to be developed.…”

Coherence orders, decoherence, and quantum metrology

“…In many applications, the second coherence order plays an important role since it indicates only spin pairs interacting through the residual dipolar coupling, which allows one to estimate the average distance between coupled spins in an amorphous solid [37][38][39]. Furthermore, when simulating localization effects induced by decoherence through a spin counting experiment [40][41][42][43], one can verify the number of correlated spins measuring the distribution of the signal among all coherence orders.…”