The crossover between low and high density regimes of exciton-polariton condensates is examined using a BCS wave-function approach. Our approach an extension the BEC-BCS theory for excitons, but includes cavity photon field. can describe both limit, where system be described as Bose-Einstein condensate (BEC) exciton-polaritons, enters photon-dominated regime. In contrast to exciton approaches electron-hole plasma, polariton limit has strongly correlated pairs. At intermediate densities,...

The second and third order coherence functions $g^{(n)}(0) (n=2 {\rm and} 3)$ of an exciton-polariton condensate is measured compared to the theory. Contrary ideal photon laser, deviation from unity in observed, thus showing a bunching effect, but not characteristics standard thermal state with $g^{(n)}(0)=n!$. increase function, $g^{(3)}(0) > g^{(2)}(0)>1$, indicates that polariton different coherent state, number state. experimental results are agreement theoretical model where...

Abstract Practical quantum communication between remote memories rely on single photons at telecom wavelengths. Although spin-photon entanglement has been demonstrated in atomic and solid-state qubit systems, the produced short wavelengths with polarization encoding are not suitable for long-distance communication, because they suffer from high propagation loss depolarization optical fibres. Establishing nodes would further require generated separate to be indistinguishable. Here, we report...

Multipartite entanglement plays a critical role in various applications of quantum internet. In these applications, the is usually shared by distant parties. Experimentally, distributed should be estimated only local measurements. Furthermore, for network experiments, it desirable to employ measurement techniques that are straightforward implement. this paper, we propose method measure arbitrary multipartite single-photon path entangled states By considering practically reasonable...

We report the generation of polarization-entangled photons by cavity-enhanced spontaneous parametric down-conversion. The bandwidth entangled is reduced to that optical parometric oscillator and conversion rate enhanced cavity. time interval between conjugate two photon prolongated so it can be directly measured a common detector. correlation function entangled-photons pair shows time-oscillatory characteristic. To demonstrate entanglement, we experimentally obtain two-photon quantum...

Recently a long distance and high key rate quantum distribution (QKD) has become possible by the idea of decoy state method. We show that longer QKD is utilizing heralded single photon source (utilizing spontaneous parametric down-conversion) as instead weak coherent pulse (WCP) proposed in original Moreover, improved presently available number resolving detector trigger it shown to approach WCP.

Bogoliubov's theory states that self-interaction effects in Bose-Einstein condensates produce a characteristic linear dispersion at low momenta. One of the curious features is new quasiparticles system are combinations creation and destruction operators bosons. In exciton-polariton condensates, this gives possibility directly observing negative branch Bogoliubov photoluminescence (PL) emission. Here we theoretically examine PL spectra taking into account reservoir effects. At sufficiently...

The ability to transmit quantum states over long distances is a fundamental requirement of the internet and reliant upon repeaters. Quantum repeaters involve entangled photon sources that emit deliver photonic at high rates memories can temporarily store states. Improvement entanglement distribution rate essential for repeaters, multiplexing expected be breakthrough. However, limited studies exist on multiplexed their coupling with memory. Here, we demonstrate storing frequency-multiplexed...

Exciton-polaritons are a coherent electron-hole-photon (e-h-p) system where condensation has been observed in semiconductor microcavities. In contrast to equilibrium Bose-Einstein (BEC) for long lifetime systems, polariton condensates have dynamical nonequilibrium feature owing the similar physical structure that they lasers. One of distinguishing features condensate laser is presence strong coupling between matter and photon fields. Irrespective its or nature, exciton-polariton maintain...

Quantum computing and quantum communication, have been greatly developed in recent years expected to contribute internet technologies, including cloud unconditionally secure communication. However, long-distance communication is challenging mainly because of optical fiber losses; repeaters are indispensable for fiber-based transmission unknown states cannot be amplified with certainty. In this study, we demonstrate a versatile entanglement source the telecom band internet, which has narrow...

Observations of polariton condensation in semiconductor microcavities suggest that polaritons can be exploited as a novel type laser with low input-power requirements. The low-excitation regime is approximately equivalent to thermal equilibrium, and higher excitation results more dominant nonequilibrium features. Although standard photon lasing has been experimentally observed the high regime, e-h pair binding still remain even high-excitation theoretically. Therefore, photoluminescence...

We demonstrate an ultrabright narrow-band two-photon source at the 1.5 -\mu m telecom wavelength for long-distance quantum communication. By utilizing a bow-tie cavity, we obtain cavity enhancement factor of $4.06\times 10^4$. Our measurement second-order correlation function $G^{(2)} ({\tau})$ reveals that linewidth $2.4$ MHz has been hitherto unachieved in band. This is useful obtaining high absorption probability close to unity by memories set inside repeater nodes. Furthermore, best our...

We analyze the generation of entanglement in a multipartite optical network. generalize twin-field strategy to case and show that our protocol has advantageous rate-loss scalings distributing $W$ states Dicke over star networks. provide precise theoretical formulas quantitative performance analyses. Also, analysis same using Gaussian as resources, which is typical setup many experimental tests, provided. numerically study feasibility realistic conditions with imperfect detectors. observe...

Frequency offset locking between two Nd:YAG lasers is performed using frequency with an electrical delay line. The relative instability of the measured to be 3.5×10−12 for averaging time 1 s, which approximately 77 times smaller than that free-running case. compared phase lasers. Furthermore, a compact solid-state laser locked optical comb 8.2×10−11 improved by 20 times, respect offset-locking scheme line useful various applications including research on quantum optics, interferometric...

Abstract In a standard semiconductor laser, electrons and holes recombine via stimulated emission to emit coherent light, in process that is far from thermal equilibrium. Exciton-polariton condensates–sharing the same basic device structure as consisting of quantum wells coupled microcavity–have been investigated primarily at densities below Mott density for signatures Bose-Einstein condensation. At high approaching density, exciton-polariton condensates are generally thought revert with...

We examine the photoluminescence of highly excited exciton-polariton condensates in semiconductor microcavities. Under strong pumping, have been observed to undergo a lasing transition where coupling between excitons and photons is lost. discuss an alternative high-density scenario, maintained. find that smoothly transitions lower polariton energy cavity photon energy. An intuitive understanding change spectral characteristics given, as well differences case.

Quantum repeaters are pivotal in the physical layer of quantum internet. For its development, capable efficient entanglement distribution necessary. repeater schemes based on single-photon interference promising due to their potential efficiency. However, involving first-order with photon sources at distant nodes require stringent phase stability components, which poses challenges for long-distance implementation. In this paper, we present a scheme that leverages reduced difficulty...

Abstract We propose a scheme to phase lock quantum-memory control laser, frequency-conversion pump and two-photon source over three octaves in frequency operate quantum memory. The absolute frequencies of the laser sources are determined based on Doppler-free iodine hyperfine transition. achieved relative instability uncertainty were ≤1 × 10 –12 3 –11 , respectively, which below requirement for operating Pr:YSO This simplifies instrumentation repeater, increases reliability communication systems.

Quantum repeaters are pivotal in the physical layer of quantum internet, and capable efficient entanglement distribution necessary for its development. repeater schemes based on single-photon interference promising because their potential efficiency. However, involving first-order with photon sources at distant nodes require stringent phase stability components, which pose challenges long-distance implementation. In this paper, we present a scheme that leverages reduces difficulty achieving...

An oscillatory correlation function has been observed by the coincidence counting of multimode two-photon pairs produced with a degenerate optical parametric oscillator far below threshold. The coherent superposition provides oscillation in intensity function. experimental data are well fitted to theoretical curve.

Long-distance quantum communication requires entanglement between distant memories. For this purpose, photon transmission is necessary to connect the Here, for first time, we develop a two-step frequency conversion process (from visible wavelength telecommunication and back) involving use of independent two-frequency media where target memories are nitrogen-vacancy centers in diamonds (with an emission/absorption 637.2 nm), experimentally characterize performance acting on light from...

Quantum repeaters are required for long-distance quantum communication. For efficient coupling of entangled photon sources with narrow-linewidth memories we performed the frequency stabilization two lasers at 1514 and 1010 nm. The nm pump laser source exhibited a stability 3.6 \times 10^{-12} (\tau = 1 s). wavelength conversion system 3.4 stabilities both were approximately orders magnitude smaller than width 4 MHz Pr:YSO memory. Such frequency-stabilized can realize remote memory an in repeaters.

Quantum repeaters are indispensable tools for long-distance quantum communication. However, frequency matching between entangled photon sources and remote memories (QMs) is difficult, which an obstacle to the implementation of repeaters. In this paper, we demonstrate a method achieve coupling Pr:YSO as fixed-time QM with single telecommunication-wavelength through stabilization using optical comb over all applied laser wavelengths. The demonstrated can lead repeater scheme enabling...