From decoherence-free channels to decoherence-free and quasi-free subspaces within bosonic dissipative networks

Abstract

We present a technique to build, within a dissipative bosonic network, decoherence-free channels (DFCs): a group of normal-mode oscillators with null effective damping rates. We verify that the states protected within the DFC define the well-known decoherence-free subspaces (DFSs) when mapped back into the natural network oscillators. Therefore, our technique to build protected normal-mode channels turns out to be an alternative way to build DFSs, which offers advantages over the conventional method. It enables the computation of all the network-protected states at once, as well as leading naturally to the concept of the decoherence quasi-free subspace (DQFS), inside which a superposition state is quasi-completely protected against decoherence. The concept of the DQFS, weaker than that of the DFS, may provide a more manageable mechanism to control decoherence. Finally, as an application of the DQFSs, we show how to build them for quasi-perfect state transfer in networks of coupled quantum dissipative oscillators.

Steady entanglement in bosonic dissipative networks

“…In fact, there is an infinite number of states that present the same fidelity regarding a given target state and the same is true for purity; thus both quantities are often used to corroborate each other [27]. We note that the master equation (2) for the case of degenerate symmetric networks contains only natural decay rates in the mode ω 1 [29], i.e., γ 1 = Nγ and γ j = 0. Therefore, to reach the target state |1,0, .…”

“…The improvement in the preparation of the entangled state is due to the cooling effect (Γ − ), which enhances the fidelity of the vacuum state in the mode ω − . We note that the master equation (2) for the case of degenerate symmetric networks contains only natural decay rates in the mode ω 1 [26], i.e. γ 1 = Nγ and γ j = 0.…”

Colored channels for high-fidelity information transfer and processing between remote multi-branch quantum circuits

“…Aiming to optimize the control required for communication between distant nodes in a QC, the research effort devoted to state transfer has led to the necessary and sufficient conditions, within spin [2] and resonator networks [3], for it to demonstrate that perfect transfer can occur in an entire class of topologies [4]. State transfer through realistic noise channels has also been addressed within spin chains [5,6] and a protocol for quasi-perfect state transfer in a network of dissipative resonators [7,8] seems to broaden the perspective on the subject of decoherence-(quasi-)free subspaces [9]. In a more recent contribution [10], the process of quasi-perfect remote state transfer has been formally characterized as a nonlocal tunneling process where -by analogy with the tunneling effect in a double-well barrier-the overlap between distant sender and the receiver wave functions is indirectly mediated by the normal modes of the data bus (DB), i.e., the transmission kernel of the network.…”