Nearly Deterministic Bell Measurement for Multiphoton Qubits and its Application to Quantum Information Processing

We propose a Bell-measurement scheme by employing a logical qubit in Greenberger-Horne-Zeilinger entanglement with an arbitrary number of photons. Remarkably, the success probability of the Bell measurement as well as teleportation of the Greenberger-Horne-Zeilinger entanglement can be made arbitrarily high using only linear optics elements and photon on-off measurements as the number of photons increases. Our scheme outperforms previous proposals using single-photon qubits when comparing the success probabilities in terms of the average photon usages. It has another important advantage for experimental feasibility in that it does not require photon-number-resolving measurements. Our proposal provides an alternative candidate for all-optical quantum information processing.

Figure 1

(a) Bell measurement for two-photon qubits using two single-photon-qubit Bell measurements $B_s$. Each logical qubit is of two photons. (b) Bell measurement for $N$-photon qubits through $N$ times of $B_s$ measurements.

Figure 2

The success probability of Bell measurements against the average photon number ($\overline{n}$) used in the process. It is given as $1-2^{-\overline{n}/2}$ for our Bell-measurement scheme (blue curve), $1-1/\overline{n}$ for Grice’s scheme (red dot-dashed curve) [6], $P_s=0.643$ with $\overline{n}=6.00029$ for the squeezing scheme (green circle) [8], and $1-2^{-\overline{n}/4}$ for scheme using ancillary photons (orange dotted curve) [7].