Zero-Area Single-Photon Pulses

Abstract

Broadband single photons are usually considered not to couple efficiently to atomic gases because of the large mismatch in bandwidth. Contrary to this intuitive picture, here we demonstrate that the interaction of ultrashort single photons with a dense resonant atomic sample deeply modifies the temporal shape of their wavepacket mode without degrading their non-classical character, and effectively generates zero-area single-photon pulses. This is a clear signature of strong transient coupling between single broadband (THz-level) light quanta and atoms, with intriguing fundamental implications and possible new applications to the storage of quantum information.Single photons are privileged carriers of quantum information because of their little interaction with the environment and among themselves. However, when it comes to storing and manipulating information, it would be useful for them to interact strongly with some atomic system in order to convert their quantum state into a stationary quantum state of matter [1]. Since atomic systems, either made of cold and ultracold atoms or of hot vapors, have absorption linewidths in the Hz to GHz range, the main road to enhance the atom-photon interaction has always been that of using sufficiently narrowband quantum photonic states, either produced in cavity-enhanced parametric down-conversion sources [2-5], or directly from cold [6][7][8][9] or hot [10, 11] atomic samples. In general, ultrashort single photons with bandwidths much broader than the atomic bandwidth are therefore not considered useful for this task because they are thought to interact only very weakly with the atoms. This is not necessarily true.Resonant interaction between ultrashort classical pulses and atomic media has long been investigated, together with some of its most peculiar effects. Two-photon transitions, for example, are well known to involve the whole bandwidth of an ultrashort pulse and to benefit considerably from the broad shaping of its spectral profile [12,13]. The formation of zero-area pulses is another spectacular consequence of the propagation of weak ultrashort pulses in the dispersive medium around an atomic resonance [14,15]. Considering a laser pulse whose description in frequency space is initially given by E(ω, 0), propagation through a distance l in the resonant medium modifies it to:where α 0 is the optical density of the medium, ω a is the atomic resonance frequency, and T 2 is the upper level lifetime. This approximate expression, which considers two-level atoms and an effective single lorentzian profile for the resonance line of the sample is enough to convey all the main features of the phenomenon. If the atomic transition is sufficiently narrow, the absorbed pulse energy can be almost negligible even in the case of high optical depths, but dispersion may still cause a dramatic re-shaping of the temporal pulse envelope. In accordance to the pulse area theorem [16][17][18], the electric field amplitude of the pulse rapidly develops a series of lobes of alternating signs ...

Engineering temporal-mode-selective frequency conversion in nonlinear optical waveguides: from theory to experiment

“…The temporal mode (TM) bases are discrete and in principle infinite dimensional, and truly orthogonal. These orthogonal modes have overlapping spectra at the same carrier frequency, fully overlap in time, and share the same polarization and transverse spatial mode properties, making them convenient for long-distance communication and interfacing with optical memories [8][9][10][11]. Co-propagating TMs maintain relative coherence across the entire mode space, and experience the same reversible unitary dispersion during propagation in typical media.…”

Monotonic convergent quantum optimal control method with exact equality constraints on the optimized control fields

“…As illustrations, the method will be performed to find optimal control fields with (i) exact zero area, and (ii) exact zero area while keeping pulse fluence constant. The time-integrated zero area field constraint for a freely propagating electromagnetic pulse is an important property for exploring coherent interaction of light with matter [30][31][32][33], and is required as a fundamental condition for satisfying the Maxwell's equations [27]. Only have there been limited attempts to take into account such constraint in the contexts of local control theory (LCT) and QOCT [27,34].…”

Single-photon hologram of a zero-area pulse

“…a femtosecond pulse passing through atomic vapor -a case broadly studied with weak coherent states and demonstrated to produce so-called zero-area or 0π pulses [18,19] with temporal envelopes consisting of alternating ± sign lobes. Recently, such an interaction has been demonstrated for single-photon states and Rb vapor [20], exploring a vastly unharnessed region of light-matter interaction between a THz-bandwidth photon and a GHz-wide (Doppler broadened) atomic transition. While the photon is rarely absorbed, the interaction is highly dispersive leaving the photon in the zero-area temporal shape and imprinting a spectral phase profile.…”