Probing Quantum Memory Effects in the Single Photon Regime

Carlos Belmonte, FREDERIK VANDEN BERGHE, Krassimir P. Panajotov +1 more

In this paper we study correlations present in experimental random series extracted from a Quantum Optical Random Number generator conceived and implemented in our lab. In particular we study the manifestations of inertia/memory effects. This study is realized in the single photon regime.

Chuan‐Feng Li

Emanuele Distante, Pau Farrera, Auxiliadora Padrón-Brito +3 more

Summary form only given. Strong interaction between two single photons [1], is a long standing and important goal in quantum photonics. This would enable a new regime of nonlinear optics and unlock several applications in quantum information science, including photon-photon gates and deterministic Bell-state measurements for quantum networking. In the context of quantum networks [2], a particularly important case is to achieve strong interaction between single photons from independent photon pairs that can be stored in quantum memories. So far, most of the efforts towards nonlinear effects at the single-photon level have been realized using weak classical input light.In this contribution, we demonstrate the storage and retrieval of a paired single photon emitted by an ensemble quantum memory in a strongly nonlinear medium based on highly excited Rydberg atomic excitations [3,4]. We demonstrate that non-classical correlations between the two photons persist after the retrieval from the Rydberg ensemble. We show that our Rydberg cold atomic ensemble displays optical nonlinearity with input pulses containing few tens of photons. Our results [5], mark an important step towards deterministic photonphoton interactions, and may enable deterministic Bell-state measurement with multimode quantum memories.

Philip John Walther, Alex Nemiroski, Mason Klein +7 more

Achal Vinod, Da-Wei Luo, Ting Yu

We investigate how photon loss and environmental memory affect probe selection and measurement sensitivity for estimating the dispersive coupling strength in a cavity qubit system. Using density operator and quantum state diffusion approaches, we examine the quantum Fisher information for representative separable and entangled initial states in Markovian and non Markovian regimes. The results show that closed system generator variance alone does not determine open system performance. The survival of parameter sensitive coherences and the influence of environmental memory also play important roles. Within the single photon preparations examined, a separable probe can outperform the entangled family considered. Comparisons of selected coherent and squeezed vacuum preparations at equal mean photon number further illustrate how photon number statistics and qubit preparation affect sensitivity. For the parameters studied, finite environmental memory can enhance and prolong sensitivity and yield nonzero QFI for a probe whose Markovian QFI vanishes. We also numerically identify a fixed Hermitian observable whose error propagation uncertainty remains close to the quantum Cramer Rao bound over a prescribed coupling interval in the Markovian regime. These findings clarify the interplay between probe preparation, environmental dynamics, and measurement choice in dispersive quantum metrology.

Salvatore Virzì, Alessio Avella, Fabrizio Piacentini +8 more

We experimentally demonstrate, for the first time, noise diagnostics by repeated quantum measurements, establishing the ability of a single photon subjected to random polarization noise to diagnose non-Markovian temporal correlations of such a noise process. Both the noise spectrum and temporal correlations are diagnosed by probing the photon with frequent (partially) selective polarization measurements. We show that noise with positive temporal correlations corresponds to our single photon undergoing a dynamical regime enabled by the quantum Zeno effect (QZE), whereas noise characterized by negative (anti) correlations corresponds to regimes associated with the anti-Zeno effect (AZE). This is the first step toward a novel noise spectroscopy based on QZE and AZE in single-photon state probing able to extract information on the noise while protecting the probe state, a conceptual paradigm shift with respect to traditional interferometric measurements.