Direct observation of broadband nonclassical states in a room-temperature light–matter interface

Abstract

Nonclassical state is an essential resource for quantumenhanced communication, computing and metrology to outperform their classical counterpart. The nonclassical states that can operate at high bandwidth and room temperature while being compatible with quantum memory are highly desirable to enable the scalability of quantum technologies. Here, we present a direct observation of broadband nonclasscal states in a room-temperature lightmatter interface, where the atoms can also be controlled to store and interfere with photons. With a single coupling pulse and far off-resonance configuration, we are able to induce a multi-field interference between light and atoms to create the desired nonclassical states by spectrally selecting the two correlated photons out of seven possible emissions. We explicitly confirm the nonclassicality by observing a cross correlation up to 17 and a violation of Cauchy-Schwarz inequality with 568 standard deviations. Our results demonstrate the potential of a state-built-in, broadband and room-temperature light-matter interface for scalable quantum information networks.

Multipartite Entanglement of Billions of Motional Atoms Heralded by Single Photon

“…To herald multipartite entanglement W state, we adopt the SRS regime as proposed in the Duan-Lukin-Cirac-Zoller (DLCZ) protocol originally aiming at realizing applicable quantum repeaters [24]. However, we have to conceive a far off-resonance scheme to avoid the huge fluorescence noise in room-temperature atomic ensemble [25,26,27], which does not exist in cold ensembles and diamonds [28,29]. The energy levels of the Λ-type configuration are shown in Figure 1a.…”

“…There are several elements that will influence the entanglement depth, such as the beam waist, the detuning, and the energy of addressing light. For the far off-resonance DLCZ protocol, we have chosen a "sweet point" for the detuning, which has been experimentally demonstrated to have the lowest unconditional noise [25,26]. As for the beam waist, it is not appropriate to utilize too large beam waist to provide enough addressing energy.…”

Photon-matter quantum correlations in spontaneous Raman scattering

“…This timing information serves to distinguish photon-CE pairs and decrease the state purity of the photon, and normally has a significantly stronger effect on the photon purity than chromatic dispersion. Here we note that whereas for Raman-active atomic vapors the effect of excitation linewidth and chromatic dispersion may be negligible, for the same media collection in the backwards direction [19,38] can strongly affect the correlations between broadband photon and excitation.…”

“…Keeping terms of O |q s | 2 /k(ω s ) 2 consistent with the paraxial approximation, the JA is given by photons collected by a lens and coupled to a singlemode fiber, assuming that the projection of the spatial mode supported by the fiber onto free space by the lens can be well approximated by a Gaussian, this configuration projects the scattered Stokes photons onto a state with creation operator † s (ω s ) given in Eq. (19). Letting |u f (ω s ) = † s (ω s )|vac , the projection of the emitted state onto this concentric collection mode, given by normalizing the state dω s |u f (ω s ) u f (ω s )|Ψ par , results in a state with the joint amplitudes given by Eqs.…”

“…Understanding these correlations and the properties of the joint photonexcitation state, especially in the low gain regime as studied here, is key to controlling Raman emission and enabling new applications for quantum communication, computation, and sensing. We anticipate this work to inform Raman scattering at the quantum level in solidstate systems [16,17] as well as atomic vapors [18,19], and thence on the implementation of quantum protocols such as the Duan-Lukin-Cirac-Zoller protocol [11] and Raman-based quantum memories [16,[20][21][22][23][24][25][26][27][28].…”