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Register a new userAnti-symmetrization reveals hidden entanglement
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Added by
Alessandro Fedrizzi
Publication date
2009
fields
Physics
and research's language is
English
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Two-photon anti-bunching at a beamsplitter is only possible if the photons are entangled in a specific state, anti-symmetric in the spatial modes. Thus, observation of anti-bunching is an indication of entanglement in a degree of freedom which might not be easily accessible in an experiment. We experimentally demonstrate this concept in the case of the interference of two frequency entangled photons with continuous frequency detunings. The principle of anti-symmetrisation of the spatial part of a wavefunction and subsequent detection of hidden entanglement via anti-bunching at a beamsplitter may facilitate the observation of entanglement in other systems, like atomic ensembles or Bose-Einstein condensates. The analogue for fermionic systems would be to observe bunching.
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We consider Bell tests in which the distant observers can perform local filtering before testing a Bell inequality. Notably, in this setup, certain entangled states admitting a local hidden variable model in the standard Bell scenario can nevertheless violate a Bell inequality after filtering, displaying so-called hidden nonlocality. Here we ask whether all entangled states can violate a Bell inequality after well-chosen local filtering. We answer this question in the negative by showing that there exist entangled states without hidden nonlocality. Specifically, we prove that some two-qubit Werner states still admit a local hidden variable model after any possible local filtering on a single copy of the state.
We discuss how introducing an equilibrium frame, in which a given Hamiltonian has balanced loss and gain terms, can reveal PT symmetry hidden in non-Hermitian Hamiltonians of dissipative systems. Passive PT-symmetric Hamiltonians, in which only loss is present and gain is absent, can also display exceptional points, just like PT-symmetric systems, and therefore are extensively investigated. We demonstrate that non-Hermitian Hamiltonians, which can be divided into a PT-symmetric term and a term commuting with the Hamiltonian, possess hidden PT symmetries. These symmetries become apparent in the equilibrium frame. We also show that the number of eigenstates having the same value in an exceptional point is usually smaller in the initial frame than in the equilibrium frame. This property is associated with the second part of the Hamiltonian.
Dissipative entanglement generation protocols embrace environmental interactions in order to generate long-lived entangled states. In this letter, we report on the anti-bunching dynamics for a pair of actively driven quantum emitters coupled to a shared dissipative plasmonic reservoir. We find that anti-bunching is a universal signature for entangled states generated by dissipative means and examine its use as an entanglement diagnostic. We discuss the experimental validation of plasmonically mediated entanglement generation by Hanbury Brown-Twiss interferometry with picosecond timing resolution determined by an effective two-qubit Rabi frequency, and we analyze the robustness of entanglement generation with respect to perturbations in local detunings, couplings, and driving fields.
It is known that entanglement dynamics of two noninteracting qubits, locally subjected to classical environments, may exhibit revivals. A simple explanation of this phenomenon may be provided by using the concept of hidden entanglement, which signals the presence of entanglement that may be recovered without the help of nonlocal operations. Here we discuss the link between hidden entanglement and the (non-Markovian) flow of classical information between the system and the environment.
Entanglement dynamics of two noninteracting qubits, locally affected by random telegraph noise at pure dephasing, exhibits revivals. These revivals are not due to the action of any nonlocal operation, thus their occurrence may appear paradoxical since entanglement is by definition a nonlocal resource. We show that a simple explanation of this phenomenon may be provided by using the (recently introduced) concept of hidden entanglement, which signals the presence of entanglement that may be recovered with the only help of local operations.
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