Improvement in quantum communication using quantum switch

Communication advantage of quantum compositions of channels from non-Markovianity

“…We are concerned with the transmission of information in our system, as well as the quantum switch's enhancement of it. Particularly, the quantum switch was shown to enhance the classical and quantum capacities [23][24][25][26][27][28], which are defined by the Holevo quantity and the coherent information. Here, we define these quantities and describe how their revival in a non-Markovian system corresponds to the revival of the entanglement monotone.…”

“…The phenomenon of indefinite causal orders has seen multiple advantages in terms of computation [15][16][17], metrology [18][19][20], and refrigeration or work extraction [21,22] tasks. Such advantages also include enhancement to communication complexities in communication games, as well as enhancements to classical and quantum capacities as compared to using the channels in series, violating the bottleneck inequality [23][24][25][26]. Like superactivation, this enhancement is even possible if the individual channels have zero capacities [27,28].…”

Effects of non-Markovianity in quantum compositions of channels with indefinite causal order

“…Nevertheless, the quantum switch can still grant various advantages in terms of communication capacities [15][16][17][18][19], computational tasks [21,[58][59][60], metrology [61][62][63], and refrigeration or work extraction tasks [64][65][66]. For example, enhancements to classical and quantum capacities can violate the bottleneck inequality of using the channels in series [15][16][17]67], that is, the resulting capacities can be greater than each individual channel allows, a phenomenon referred to as causal activation, i.e., 𝐶 𝑖 Φ sw ≥ max {𝐶 𝑖 (Φ 𝐴 ) , 𝐶 𝑖 (Φ 𝐵 )}, where 𝐶 𝑖 is the communication capacity of a channel. Like superactivation, this enhancement is even possible if the individual channels have zero capacities [18,19].…”

“…Now that we have a non-Markovian framework that encompass the three channel compositions Φ sw , Φ traj , and Φ indep , we can look into how non-Markovian effects might play a role or explain the quantum switch's enhancements to communication capacities. Particularly, the quantum switch was shown to enhance the classical and quantum capacities [15][16][17][18][19]67], which are defined by the Holevo quantity and the coherent information.…”