Indistinguishability of Elementary Systems as a Resource for Quantum Information Processing

Typical elements of quantum networks are made by identical systems, which are the basic particles constituting a resource for quantum information processing. Whether the indistinguishability due to particle identity is an exploitable quantum resource remains an open issue. Here we study independently prepared identical particles showing that, when they spatially overlap, an operational entanglement exists that can be made manifest by means of separated localized measurements. We prove this entanglement is physical in that it can be directly exploited to activate quantum information protocols, such as teleportation. These results establish that particle indistinguishability is a utilizable quantum feature and open the way to new quantum-enhanced applications.

Figure 1

Operational entanglement. Two identical particles with opposite pseudospins (internal states) have spatial wave functions $\psi$, ${\psi }^{\prime }$ with a given degree of overlap. The entanglement between pseudospins is operationally defined by local measurements in two separated localized spatial regions $L$ and $R$.

Figure 2

A paradigmatic system. Two identical particles with opposite pseudospins have overlapping spatial wave functions $\psi$, ${\psi }^{\prime }$ peaked in two separated localized regions $L$, $R$. Their pseudospins are addressed by local measurements on $L$ and $R$.

Figure 3

Teleportation scheme. Two identical particles with opposite pseudospins have the same spatial wave function ${\psi }_0$ peaked in two separated regions $L$ and $R$. A third particle, distinguishable from the others, is placed in $L^{\prime }$ close to $L$, yet separated from it and prepared in an arbitrary pseudospin state. Direct application of the standard teleportation protocol in the two laboratories individuated by ($L^{\prime }$, $L$) and $R$ allows the conditional transfer of this arbitrary state from a laboratory to another. The pseudospin of the particle in $L^{\prime }$ is finally entangled with the pseudospin of one of the two particles in $L$.