Optical quantum memory--the ability to store photonic quantum states and retrieve them on demand--is an essential resource for emerging quantum technologies and photonic quantum information protocols. Simultaneously achieving high efficiency and high-speed, broadband operation is an important task necessary for enabling these applications. In this work, we investigate the optimization of a large class of optical quantum memory protocols based on resonant interaction with ensembles of $Λ$-type level systems with the restriction that the temporal envelope of all optical fields must be Gaussian, which reduces experimental complexity. We show that for overlapping signal and control fields there exists a unique and broadband pulse duration that optimizes the memory efficiency, and that this optimized efficiency can be close to the protocol-independent bound. We further optimize over the control field temporal delay and pulse duration, demonstrating saturation of this efficiency bound over a broad range of pulse durations while clarifying the underlying physics of the quantum memory interaction.
Quantum memories, devices that can store and retrieve photonic quantum states on demand, are essential components for scalable quantum technologies. It is desirable to push the memory towards the broadband regime in order to increase the data rate. Here, we present a theoretical and experimental study on the broadband optical memory based on electromagnetically-induced-transparency (EIT) protocol. We first provide a theoretical analysis on the issues and requirements to achieve a broadband EIT memory. We then present our experimental efforts on EIT memory in cold atoms towards the broadband or…
Broadband implementations of time-optimal geodesic pulse elements are introduced for the efficient creation of effective trilinear coupling terms for spin systems consisting of three weakly coupled spins 1/2. Based on these pulse elements, the time-optimal implementation of indirect SWAP operations is demonstrated experimentally. The duration of indirect SWAP gates based on broadband geodesic sequence is reduced by 42.3% compared to conventional approaches.
A general approach is introduced for the efficient simultaneous optimization of pulses that compensate each other' s imperfections within the same scan. This is applied to broadband Ramsey-type experiments, resulting in pulses with significantly shorter duration compared to individually optimized broadband pulses. The advantage of the cooperative pulse approach is demonstrated experimentally for the case of two-dimensional nuclear Overhauser enhancement spectroscopy. In addition to the general approach, a symmetry-adapted analysis of the optimization of Ramsey sequences is presented. Furthermo…
To the best of our knowledge, we demonstrate for the first time the generation of photon number squeezing by spectral filtering for ultra-broadband light generated by microstructure fibers at 800 nm. A maximum squeezing of 4.6 dB is observed, corresponding to 10.3 dB after correcting for detection losses. We numerically analyzed the quantum dynamics of ultrashort laser pulse propagation through optical fibers by solving a nonlinear quantum Schrodinger equation that included Raman scattering, especially for the quantum correlation of photon number fluctuation among frequency modes in broadband …
Swept-frequency pulses have found applications in a wide range of areas including spectroscopic techniques where efficient control of spins is required. For many of these applications, a good understanding of the evolution of spin systems during these pulses plays a vital role, not only in describing the mechanism of techniques, but also in enabling new methodologies. In magnetic resonance spectroscopy, broadband inversion, refocusing, and excitation using these pulses are among the most used applications in NMR, ESR, MRI, and $in$ $vivo$ MRS. In the present survey, a general expression for ch…
We demonstrate broadband laser cooling of atomic ions in an rf trap using ultrafast pulses from a modelocked laser. The temperature of a single ion is measured by observing the size of a time-averaged image of the ion in the known harmonic trap potential. While the lowest observed temperature was only about 1 K, this method efficiently cools very hot atoms and can sufficiently localize trapped atoms to produce near diffraction-limited atomic images.
It is showed on the basis of the multiple-quantum operator algebra space formalism that ultra-broadband heteronuclear Hartmann-Hahn polarization transfer could be achieved by the amplitude- and frequency-modulation quasi-adiabatic excitation (90 degree) pulses, while it is usually difficult for the adiabatic inversion pulses to achieve effectively broadband Hartmann-Hahn transfer in a heteronuclear coupled two-spin system. The adiabatic and quasi-adiabatic pulses have an important property that within their activation bandwidth flip angle of the pulses is independent of the pulse duration and …
We report the experimental demonstration of coherent control with high power, broadband squeezed vacuum. Although incoherent and exhibiting the statistics of a thermal noise, broadband squeezed vacuum is shown to induce certain two-photon interactions as a coherent ultrashort pulse with the same spectral bandwidth. Utilizing pulse-shaping techniques we coherently control the sum-frequency generation of broadband squeezed vacuum over a range of two orders of magnitude. Coherent control of two-photon interactions with broadband squeezed vacuum can potentially obtain spectral resolutions and exti…
We experimentally demonstrate two-photon absorption (TPA) with broadband down-converted light (squeezed vacuum). Although incoherent and exhibiting the statistics of a thermal noise, broadband down-converted light can induce TPA with the same sharp temporal behavior as femtosecond pulses, while exhibiting the high spectral resolution of the narrowband pump laser. Using pulse-shaping methods, we coherently control TPA in Rubidium, demonstrating spectral and temporal resolutions that are 3-5 orders of magnitude below the actual bandwidth and temporal duration of the light itself. Such properties…
We analyze the storage and retrieval of intense-broadband pulses with the added effects of Doppler broadening and detuning in a $Λ$ configuration. We compute analytical solutions via the inverse scattering technique and show how the signal field is transferred to a spin-wave in the atomic medium and later retrieved by the interaction of a control pulse. Due to the intensity of the pulses, the pulse area (as defined for self-induced transparency) plays a key role in the interaction, as it determines the location of the spin wave within the medium. Additionally, we compare our results to non-ide…
Superradiance, characterized by the collective, coherent emission of light from an excited ensemble of emitters, generates photonic signals on timescales faster than the natural lifetime of an individual atom. The rapid exchange of coherence between atomic emitters and photonic fields in the superradiant regime enables a fast, broadband quantum memory. We demonstrate this superradiance memory mechanism in an ensemble of cold rubidium atoms and verify that this protocol is suitable for pulses on timescales shorter than the atoms' natural lifetime. Our simulations show that the superradiance mem…
We propose a new technique for comparing two Raman active samples. The method employs optical interference of the signals generated via coherent anti-Stokes Raman scattering (CARS) of broadband laser pulses with noisy spectra. It does not require spectrally resolved detection, and no prior knowledge about either the Raman spectrum of the samples, or the spectrum of the incident light is needed. We study the proposed method theoretically, and demonstrate it in a proof-of-principle experiment on Toluene and ortho-Xylene samples.
We introduce the concept of a quantum pulse gate (QPG), a method for accessing the intrinsic broadband spectral mode structure of ultrafast quantum states of light. This mode structure can now be harnessed for applications in quantum information processing. We propose an implementation in a PPLN waveguide, based on spectrally engineered sum frequency generation (SFG). It allows us to pick well-defined spectral broadband modes from an ultrafast multi-mode state for interconversion to a broadband mode at another frequency. By pulse-shaping the bright SFG pump beam, different orthogonal broadband…
Expressions for the two-dimensional Stimulated x-ray Raman Spectroscopy (2D-SXRS) signal obtained using attosecond x-ray pulses are derived. The 1D- and 2D-SXRS signals are calculated for trans-N-methyl acetamide (NMA) with broad bandwidth (FWHM ~14.2eV, 181 as) pulses tuned to the oxygen and nitrogen K-edges. Crosspeaks in 2D signals reveal electronic Franck-Condon overlaps between valence orbitals and relaxed orbitals in the presence of the core hole.
We investigated the optimal spectral design of periodic structure of narrow lines (AFC-structure) within the inhomogeneously broadened atomic transition which are created for the implementation of broadband AFC photon echo quantum memory.The influence of the spectral design on the suppression of negative dispersion effects in the AFC-echo retrieval was studied for different spectroscopic parameters of atomic media. The maps of the assigned spectral quantum efficiency have been constructed for the created AFC-structures characterized by different spectral design, finesse and optical depth. Base…
We seek to design experimentally feasible broadband, temporally multiplexed optical quantum memory with near-term applications to telecom bands. Specifically, we devise dispersion compensation for an impedance-matched narrow-band quantum memory by exploiting Raman processes over two three-level atomic subensembles, one for memory and the other for dispersion compensation. Dispersion compensation provides impedance matching over more than a full cavity linewidth. Combined with one second spin-coherence lifetime the memory could be capable of power efficiency exceeding 90% leading to 106 modes f…
We present a solution to the problem of broadband decoupling of a coupled homonuclear two-spin system. We describe a pulse sequence that creates an effective field perpendicular to the coupling interaction with a magnitude propotional to the chemical shift of the spins over a broad range of chemical shifts. When the chemical shift difference as imprinted on the perpendicular field is greater than the coupling between the spins, we get effective decoupling. The pulse sequence may be useful in various NMR applications.
We analyze a quantum optical memory based on the off-resonant Raman interaction of a single broadband photon, copropagating with a classical control pulse, with an atomic ensemble. The conditions under which the memory can perform optimally are found, by means of a `universal' mode decomposition. This enables the memory efficiency to be specified in terms of a single parameter, and the control field pulse shape to be determined via a simple nonlinear scaling. We apply the same decomposition to determine the optimal configurations for read-out.
Pulsed excitation of broad spectra requires very high field strengths if monochromatic pulses are used. If the corresponding high power is not available or not desirable, the pulses can be replaced by suitable low-power pulses that distribute the power over a wider bandwidth. As a simple case, we use microwave pulses with a linear frequency chirp. We use these pulses to excite spectra of single NV-centers in a Ramsey experiment. Compared to the conventional Ramsey experiment, our approach increases the bandwidth by at least an order of magnitude. Compared to the conventional ODMR experiment, t…
The absorption of a single photon that excites a quantum system from a low to a high energy level is an elementary process of light-matter interaction, and a route towards realizing pure single-photon absorption has both fundamental and practical implications in quantum technology. Due to nonlinear optical effects, however, the probability of pure single-photon absorption is usually very low, which is particularly pertinent in the case of strong ultrafast laser pulses with broad bandwidth. Here we demonstrate theoretically a counterintuitive coherent single-photon absorption scheme by eliminat…
We show that the duration of broadband universal control pulses can be halved by choosing control targets with a quadratic function of phase dispersion. This class of control pulses perform a broadband universal rotation around an axis, in the Bloch sphere representation of two-level systems, given by this phase dispersion function. We present an effective optimal control method to avoid the problem of convergence to local extrema traps.
The generation of large multiphoton quantum states - for applications in computing, metrology, and simulation - requires a network of high-efficiency quantum memories capable of storing broadband pulses. Integrating these memories into a fibre offers a number of advantages towards realising this goal: strong light-matter coupling at low powers, simplified alignment, and compatibility with existing photonic architectures. Here, we introduce a large-core kagome-structured hollow-core fibre as a suitable platform for an integrated fibre-based quantum memory with a warm atomic vapour. We demonstra…
A quantum state light-storage, using a virtual magnetic field through the ac Stark effect is proposed to combine the high overall storage efficiency and large bandwidth employing room temperature atomic vapor. In this approach, which was called the ac Stark Gradient Echo Memory (ASGEM), it has been shown the possibility to employ about a nanosecond ac Stark pulse far detuned (about 127 THz) from D1 line of rubidium and create an atomic media with the possibility to store a photon with about a GHz bandwidth with storage and retrieval efficiency of more than 90%. A contour plot of efficiency as …
It is shown that inhomogeneous broadening of the spectral line of active impurities may sustain simultaneously parity (P) and time (T) symmetries of a medium, in a finite range of field frequencies, what is forbidden by the causality principle in media without broadening. If a spectral width of a propagating pulse is less than the inhomogeneous broadening, the medium for such a pulse becomes quasi-PT symmetric. The effect of the broadband quasi-PT symmetry in a finite frequency domain, is illustrated on examples of unidirectional diffraction of pulses in Bragg and Laue geometries, propagating …
Faithful storage and coherent manipulation of quantum optical pulses are key for long distance quantum communications and quantum computing. Combining these functions in a light-matter interface that can be integrated on-chip with other photonic quantum technologies, e.g. sources of entangled photons, is an important step towards these applications. To date there have only been a few demonstrations of coherent pulse manipulation utilizing optical storage devices compatible with quantum states, and that only in atomic gas media (making integration difficult) and with limited capabilities. Here …
Quantum systems with sublevel structures prevent full population inversion from one manifold of sublevels to the other using strong ultrafast resonant pulses. In this work we explain the mechanism by which this population transfer is blocked. We then develop a novel concept of geometric control, assuming full or partial coherent manipulation within the manifolds and show that by preparing specific coherent superpositions in the initial manifold, full population inversion or full population blockade, {\it i.e} laser-induced transparency, can be achieved. In particular, by parallel population tr…
Using a home-built Ku band ESR spectrometer equipped with an arbitrary waveform generator and a stripline resonator, we implement two types of pulses that would benefit quantum computers: BB1 composite pulse and a microwave frequency comb. Broadband type 1 (BB1) composite pulse is commonly used to combat systematic errors but previous experiments were carried out only on extremely narrow linewidth samples. Using a sample with a linewidth of 9.35 MHz, we demonstrate that BB1 composite pulse is still effective against pulse length errors at a Rabi frequency of 38.46 MHz. The fast control is real…
Quantum memory capable of stopping flying photons and storing their quantum coherence is essential for scalable quantum technologies. A room-temperature broadband quantum memory will enable the implementation of large-scale quantum systems for real-life applications. Due to either intrinsic high noises or short lifetime, it is still challenging to find a room-temperature broadband quantum memory beyond conceptual demonstration. Here, we present a far-off-resonance Duan-Lukin-Cirac-Zoller (FORD) protocol and demonstrate the broadband quantum memory in room-temperature atoms. We observe a low un…
Broadband quantum memories hold great promise as multiplexing elements in future photonic quantum information protocols. Alkali vapour Raman memories combine high-bandwidth storage, on-demand read-out, and operation at room temperature without collisional fluorescence noise. However, previous implementations have required large control pulse energies and suffered from four-wave mixing noise. Here we present a Raman memory where the storage interaction is enhanced by a low-finesse birefringent cavity tuned into simultaneous resonance with the signal and control fields, dramatically reducing the…
We study an initially inverted three-level atom in the lambda configuration embedded in a waveguide, interacting with a propagating single-photon pulse. Depending on the temporal shape of the pulse, the system behaves either as an optimal universal cloning machine, or as a highly efficient deterministic source of maximally entangled photon pairs. This quantum transistor operates over a wide range of frequencies, and can be implemented with today's solid-state technologies.
The paper describes the design of broadband excitation pulses in high resolution NMR by method of double sweep. We first show the design of a pulse sequence that produces broadband excitation to the equator of Bloch sphere with phase linearly dispersed as frequency. We show how this linear dispersion can then be refocused by nesting free evolution between two adiabatic inversions (sweeps). We then show how this construction can be generalized to exciting arbitrary large bandwidths without increasing the peak rf-amplitude and by incorporating more adiabatic sweeps. Finally, we show how the basi…
Driving on an analogy with the technique of composite pulses in quantum physics, we propose highly efficient broadband polarization converters composed of sequences of ordinary retarders rotated at specific angles with respect to their fast-polarization axes.
This article gives an overview on recent theoretical progress in controlling the charge and spin dynamics in low-dimensional electronic systems by means of ultrashort and ultrabroadband electromagnetic pulses. A particular focus is put on sub-cycle and single-cycle pulses and their utilization for coherent control. The discussion is mostly limited to cases where the pulse duration is shorter than the characteristic time scales associated with the involved spectral features of the excitations. We work out that the pulse action amounts in essence to a quantum map between the quantum states of th…
Microwave quantum memory promises advanced capabilities for noisy intermediate-scale superconducting quantum computers. Existing approaches to microwave quantum memory lack complete combination of high efficiency, long storage time, noiselessness and multi-qubit capacity. Here we report an efficient microwave broadband multimode quantum memory. The memory stores two spectral modes of single photon level microwave radiation in on-chip system of eight coplanar superconducting resonators. Single mode storage shows a power efficiency of up to $60\pm 3\%$ at single photon energy and more than $73\p…
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 …
It is proposed that the ground-state manifold of the neutral nitrogen-vacancy center in diamond could be used as a quantum two-level system in a solid-state-based implementation of a broadband, noise-free quantum optical memory. The proposal is based on the same-spin $Λ$-type three-level system created between the two E orbital ground states and the A$_1$ orbital excited state of the center, and the cross-linear polarization selection rules obtained with the application of transverse electric field or uniaxial stress. Possible decay and decoherence mechanisms of this system are discussed, and …
In this paper we experimentally demonstrated a broadband microwave scheme suitable for the multiresonator quan- tum memory-interface. The microwave scheme consists of the system of composed mini-resonators strongly inter- acting with a common broadband resonator coupled with the external microwave waveguide. We have implemented the controllable tuning of the mini-resonator frequencies and coupling of the common resonator with the external waveguide for the implementation of the impedance matched quantum storage. The storage of microwave pulses with an efficiency of 16.3% has been shown experim…
We study ultra-broadband slow light in a warm Rubidium vapor cell. By working between the D1 and D2 transitions, we find a several-nm window centered at 788.4 nm in which the group index is highly uniform and the absorption is small (<1%). We demonstrate that we can control the group delay by varying the temperature of the cell, and observe a tunable fractional delay of 18 for pulses as short as 250 fs (6.9 nm bandwidth) with a fractional broadening of only 0.65 and a power leakage of 55%. We find that a simple theoretical model is in excellent agreement with the experimental results. Using th…
In this paper, we propose a scheme of a long-lived broadband superefficient multiresonator quantum memory in which a common resonator is connected with an external waveguide and with a system of high-quality miniresonators containing long-lived resonant electron spin ensembles. The scheme with 4 miniresonators has been analyzed in details and it was shown that it is possible to store an input broadband signal field to the electron spin ensembles with quantum efficiency 99.99%. The considered multiresonator system opens the way to elaboration of efficient multiqubit quantum memory devices for s…
