Compact entanglement distillery using realistic quantum memories

Abstract

We adopt the beam splitter model for losses to analyse the performance of a recent compact continuous-variable entanglement distillation protocol [Phys. Rev. Lett. 108, 060502, (2012)] implemented using realistic quantum memories. We show that the decoherence undergone by a two-mode squeezed state while stored in a quantum memory can strongly modify the results of the preparatory step of the protocol. We find that the well-known method for locally increasing entanglement, phonon subtraction, may not result in entanglement gain when losses are taken into account. Thus, we investigate the critical number mc of phonon subtraction attempts from the matter modes of the quantum memory. If the initial state is not de-Gaussified within mc attempts, the protocol should be restarted to obtain any entanglement increase. Moreover, the condition mc > 1 implies an additional constraint on the subtraction beam splitter interaction transmissivity, viz. it should be about 50% for a wide range of protocol parameters. Additionally, we consider the average entanglement rate, which takes into account both the unavoidable probabilistic nature of the protocol and its possible failure as a result of a large number of unsuccessful subtraction attempts. We find that a higher value of the average entanglement can be achieved by increasing the subtraction beam splitter interaction transmissivity. We conclude that the compact distillation protocol with the practical constraints coming from realistic quantum memories allows a feasible experimental realization within existing technologies.

Continuous-Variable Quantum Computing in Optical Time-Frequency Modes Using Quantum Memories

“…The interval between storage and read-out therefore provides a period in which multiple attempts can be made at generating suitable non-linear states. The use of quantum memories to increase the success rate of photon subtraction has been studied in recent papers on entanglement distillation [38,39].…”

“…If, in Eq. 1, the classical limit of the âi field-mode is instead taken, replacing âi with γ i , two-mode squeezing (TMS) can be generated [37] between the âj mode and the stationary b mode [34,38,39]…”

Chaotic spin-spin entanglement on a recursive lattice

“…Various protocols, applicable to continuous-and discrete-variable systems have been proposed recently, allowing one to generate entanglement shared between quantum memories [6] and encoded in states of light fields [7] or, alternatively, to create systems of strongly entangled superconducting or cavity QED qubits, quantum dots, highly excited Rydberg atoms [8][9][10], etc. Meanwhile, solid-state systems and, particularly, magnetic materials, are of significant importance in this respect as they appear to be a source of entanglement too, even on a macroscopic level [11,12].…”

Entanglement, magnetic and quadrupole moments properties of the mixed spin Ising–Heisenberg diamond chain

“…It is known that the system wavefunction, in general, cannot be factorized into a direct product of subsystem states due to the nature of quantum entanglement. This phenomenon, that does not appear in the classical theory, is under great attention due to its importance in various aspects of quantum information science, ranging from discrete to continuous variable quantum computation and communication [2,3,4,5]. Even more, being a correlational measure by nature, entanglement can be a crucial characteristic of QPTs [6,7].…”