Abstract
Strong correlation of photons, particularly in the single-photon regime, has recently been exploited for various applications in quantum information processing. Existing correlation measurements, however, do not fully characterize multi-photon correlation in a relevant context and may pose limitations in practical situations. We propose a conceptually rigorous, but easy-to-implement, criterion for detecting correlated multi-photon emission out of a quantum optical system, drawn from the context of wavefunction collapse. We illustrate the robustness of our approach against experimental limitations by considering an anharmonic optical system.
Highlights
Strong correlation of photons at the few quanta level can make possible a variety of nonlinear optical devices useful for quantum information processing, such as single-photon transistors or switching devices [1, 2] and the generation of single photons on demand [3, 4]
The effective on-site repulsion between photons can be exploited to study quantum phase transitions such as the Mott-superfluid transition [5, 6, 7, 8] and the fermionization of bosons [9]. These applications are closely related to a specific correlation effect, namely a single-photon blockade effect [2, 3, 10, 11] —Once a system is excited by one photon, the abosorption of photons is blocked, e.g., due to the anharmonic energy level structure of the system
Interest in the correlation effect has been extended to multi-photon level in the context of multi-photon gateway, where a random (Poissonian) stream of photons can be converted into a bunch of temporally correlated n photons
Summary
Strong correlation of photons at the few quanta level can make possible a variety of nonlinear optical devices useful for quantum information processing, such as single-photon transistors or switching devices [1, 2] and the generation of single photons on demand [3, 4]. Correlation of photons is measured by the nth-order coherence functions introduced by Glauber [17], g(n)(0) = a†nan / a†a n, where a (a†) is the annihilation (creation) operator of an optical field It is noted in the recent experiments of cavity QED [2, 3, 12] that g(2)(0) is not effective to resolve the correlated two photon emission due to a huge bunching at the atom-cavity bare resonance overshadowing the two-photon resonance. We illustrate the power of our method in an optical cavity QED system, where genuine n-photon correlated emissions can be efficiently verified in accordance with its anharmonic energy levels
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