Experimental realization of macroscopic coherence by phase-covariant cloning of a single photon

Abstract

We investigate the multiphoton states generated by high-gain optical parametric amplification of a single injected photon, polarization encoded as a "qubit." The experiment configuration exploits the optimal phasecovariant cloning in the high gain regime. The interference fringe pattern showing the nonlocal transfer of coherence between the injected qubit and the mesoscopic amplified output field involving up to 4000 photons has been investigated. A probabilistic method to extract full information about the multiparticle output wave function has been implemented.

Cloning entangled photons to scales one can see

“…qubits on a grand circle of the Poincaré sphere can be realized by parametric amplification, as has been demonstrated for large numbers of clones by the Rome group [13,14] who did a brilliant work that stimulated ours. If the pump of the amplifier is treated as a classical field then it does not retain any information on the number of photons (n) that have been transferred into the amplified mode.…”

Generation of Highly Resilient to Decoherence Macroscopic Quantum Superpositions via Phase-covariant Quantum Cloning

“…We believe that this lucky and quite unexpected behavior is at the core of the high resilience to decoherence of our QI-OPA MQS solution. Note that this behavior was responsible for the well resolved interference pattern with visibility: V ≈ 20% obtained in absence of O-Filter (OF) by [22]. As a trivial remark, note that in all figures of the present work the function D(x) necessarily drops to zero for n N , the total number of particles associated to the macrostates.…”

“…The POVM like technique [41] implied by this device locally selects the events for which the difference between the photon numbers associated with two orthogonal polarizations |m − n| > k, i.e. larger than an adjustable threshold, k [22]. A scheme of the selected Fock-space regions by the O-Filter is reported in Fig.…”

“…Indeed, precisely the process of "quantum cloning" was there responsible for the transfer of the entanglement and the superposition properties of a pure single-particle qubit into a multiparticle MQS. In other words, the QI-OPA encoded "optimally" into a Macro-state the information associated with the input Microstate, a seed qubit [18][19][20][21][22][23]. By this device, that includes an Orthogonality Filter (O-Filter) for enhanced state discrimination, the Micro-Macro state non-separability was successfully tested and the Micro-Macro violation of the Bell inequalities for Spin-1 excitations was attained [15,24].…”

Resilience to decoherence of the macroscopic quantum superpositions generated by universally covariant optimal quantum cloning

“…larger than an adjustable threshold, k [8]. By this method a sharper discrimination between the output states |Φ 1ψ U and |Φ 1ψ ⊥ U can be achieved.…”