Coherent Superpositions of Photon Creation Operations and Their Application to Multimode States of Light

Abstract

We present a concise review of recent experimental results concerning the conditional implementation of coherent superpositions of single-photon additions onto distinct field modes. Such a basic operation is seen to give rise to a wealth of interesting and useful effects, from the generation of a tunable degree of entanglement to the birth of peculiar correlations in the photon numbers and the quadratures of multimode, multiphoton, states of light. The experimental investigation of these properties will have an impact both on fundamental studies concerning, for example, the quantumness and entanglement of macroscopic states, and for possible applications in the realm of quantum-enhanced technologies.

Remote Phase Sensing by Coherent Single Photon Addition

“…[5][6][7] The quantum Fisher information F Q [Ψ(𝜙, 𝛼)] quantifies the maximal sensitivity of the state Ψ(𝜙, 𝛼), which may be attained by an unconstrained optimization over the measurement observable, [22] that is, by considering also measurements beyond homodyne techniques. Here, we obtain F Q [Ψ(𝜋, 𝛼)] = 2|𝛼| 2 + 1, which corresponds to the total mean number of photons in the heralded state (1). An optimal quadrature measurement thus achieves the best possible sensitivity scaling with the mean number of photons in Alice's modes, whereas a quantum-optimal measurement would be able to improve the prefactor.…”

“…The detection of a single photon after Bob's BS heralds the delocalized addition of a single photon [1] and the generation of entanglement between the two signal modes in Alice's lab, yielding the state…”

“…The detection of a single photon after Bob's BS heralds the delocalized addition of a single photon [ 1 ] and the generation of entanglement between the two signal modes in Alice's lab, yielding the state $$$$\begin{align} \hspace*{90pt}|\Psi (\phi )\rangle =\mathcal {N}(\hat{a}_1^{\dagger }+e^{i\phi }\hat{a}_2^{\dagger })\mathinner {|{\alpha }\rangle }_1 \mathinner {|{\alpha }\rangle }_2 \end{align}$$$$where $$\mathcal {N}=1/\sqrt {2(1+(1+\cos (\phi ))|\alpha |^2)}$$. The phase between the idler modes in B thus determines the phase ϕ of the operator superposition, and the heralded state in A changes correspondingly.…”

Quantum Optics Parity Effect on Generalized NOON States and Its Implications for Quantum Metrology

“…The feasibility and practical relevance of this physical model rely on advances in engineering multimodal states of radiation [ 29 ] and two‐photon couplings (see ref. [57] and references therein), as well as on the experimental evidence that it is possible to create physical conditions such that a molecule inside an optical cavity behaves like a quantum two‐level system.…”

“…[19,22] One of the major problems encountered in the development of these quantum-enhanced technologies is the fragility of the required entangled states, due to the coupling with the environment and related noise. [8,23] Nevertheless, significant advances in the generation of entangled states of light [24][25][26][27][28][29] and vibrations, [30] DOI: 10.1002/andp.202200304 as well as in trapping atoms and controlling their coupling to light, [11] prompt important developments in quantum entanglement-based technologies that are adequately robust with respect to noise to enable quantum-enhanced applications.…”