Brain ageing represents a general and evolutionarily conserved phenomenon and is marked by gradual declines in cognitive functions such as learning and memory. As a synaptic coincidence detector, the N-methyl-d-aspartate (NMDA) receptor is known to be essential for the induction of synaptic plasticity and memory formation. Here, we test the hypothesis that up-regulation of NR2B expression is beneficial for learning and memory in the aged animals. Our in vitro recordings show that the aged transgenic mice with the forebrain-specific overexpression of the NR2B subunit indeed exhibit more robust hippocampal long-term potentiation (LTP) induced by either high-frequency stimulation or theta-stimulation protocol. Furthermore, those aged NR2B transgenic mice consistently outperform their wild-type littermates in five different learning and memory tests, namely, novel object recognition, contextual and cued fear conditioning, spatial reference memory, and spatial working memory T-maze task. Thus, we conclude that increased expression of NR2B in the forebrain improves learning and memory function in the aged brain.

Quantum correlations and entanglement shared among multiple quantum modes are important for both fundamental science and the future development of quantum technologies. This development will also require an efficient quantum interface between multimode quantum light sources and atomic ensembles, which makes it necessary to implement multimode quantum light sources that match the atomic transitions. Here, we report on such a source that provides a method for generating quantum correlated beams that can be extended to a large number of modes by using multiple four-wave mixing (FWM) processes in hot rubidium vapor. Experimentally, we show that two cascaded FWM processes produce strong quantum correlations between three bright beams but not between any two of them. In addition, the intensity-difference squeezing is enhanced with the cascaded system to -7.0±0.1  dB from the -5.5±0.1/-4.5±0.1  dB squeezing obtained with only one FWM process. One of the main advantages of our system is that as the number of quantum modes increases, so does the total degree of quantum correlations. The proposed method is also immune to phase instabilities due to its phase insensitive nature, can easily be extended to multiple modes, and has potential applications in the production of multiple quantum correlated images.

Precise information about the temporal mode of optical states is crucial for optimizing their interaction efficiency between themselves and/or with matter in various quantum communication devices. Here we propose and experimentally demonstrate a method of determining both the real and imaginary components of a single photon's temporal density matrix by measuring the autocorrelation function of the photocurrent from a balanced homodyne detector at multiple local oscillator frequencies. We test our method on single photons heralded from biphotons generated via four-wave mixing in an atomic vapor and obtain excellent agreement with theoretical predictions for several settings. Keywords: autocorrelation matrix; polychromatic optical heterodyne tomography; single photon; temporal mode function INTRODUCTIONSingle photons and single photon qubits are among the foundations of most quantum optical information processing techniques such as cryptography, 1 teleportation, 2 repeaters 3 and computing. 4 Many of these applications require the photons to have a well-defined, pure modal structure. Possessing precise information about that structure is essential for quantum optical technology.An approximate guess of a photon's mode can be inferred theoretically from the characteristics of the source, 5-9 but this information is not always available or reliable. For example, this approach would not work for photons sent in by a remote party in a communication scheme, or for photons from an incompletely characterized mesoscopic source. Therefore, it is important to have a technique for precise characterization of a photon's mode experimentally. While such techniques are relatively well developed for spatial modes, 10,11 their extension into the temporal domain is challenging.One approach to studying the temporal structure of the photon would be to look at the photon detection event statistics as a function of time. For example, this approach has been used to study the timing of coherent double Raman scattering from an atomic ensemble. 12 Further insight into the photon preparation quality can be gained by studying time-dependent photon counting autocorrelation statistics. 13 However, these techniques provide no information about the phase coherence between different segments of the photon's temporal mode.Complete information about a photon's temporal properties can be obtained by studying its interference with a classical field. Polycarpou et al. used adaptive waveform shaping of local oscillator (LO) pulses 14 to heuristically find the LO temporal mode that maximizes the efficiency of homodyne detection of the photon. This occurs when the LO temporal mode matches that of the signal, enabling measurement of that mode. However, physical shaping of LO pulses is quite sophisticated experimentally. Furthermore, this technique has only been demonstrated for pure temporal modes.An alternative approach to measuring the spectral density matrix of the photon has been proposed in Ref.15. It is based on bringing the photon into interference ...

The deterministic teleportation of optical modes over a 6.0-km fiber channel is realized with continuous variable entanglement.