Weak Optical Pulse Research Articles

Efficient cavity-assisted storage of photonic qubits in a solid-state quantum memory.

We report on the high-efficiency storage and retrieval of weak coherent optical pulses and photonic qubits in a cavity-enhanced solid-state quantum memory. By using an atomic frequency comb (AFC) memory in a Pr3+:Y2SiO5 crystal embedded in an impedance-matched cavity, we stored weak coherent pulses at the single photon level with up to 62% efficiency for a pre-determined storage time of 2 µs. We also confirmed that the impedance-matched cavity enhances the efficiency for longer storage times up to 70 µs. Harnessing the temporal multimodality of the AFC scheme, we stored weak coherent time-bin qubits with a record (51 ± 2%) efficiency and a fidelity over (94.8 ± 1.4)%, limited by imperfections in the qubits creation and measurement.

Optical transmitter for time-bin encoding quantum key distribution

We introduce an electro-optical arrangement that can produce time-bin encoded symbols with the decoy state method over a standard optical fiber in the C-band telecom window. The device consists of a specifically designed pulse pattern generator for pulse production and a field-programmable gate array that controls timing and synchronization. The electrical pulse output drives a sequence of intensity modulators acting on a continuous laser that deliver bursts of weak optical pulse pairs of discrete intensity values. Such a transmitter allows for the generation of all the quantum states needed to implement a discrete variable quantum key distribution (QKD) protocol over a single-mode fiber channel. Symbols are structured in bursts; the minimum relative delay between pulses is 1.25 ns, and the maximum symbol rate within a burst is 200 MHz. We tested the transmitter on simulated optical channels of 7 dB and 14 dB loss, obtaining maximum extractable secure key rates of 3.0 kb/s and 0.57 kb/s, respectively. Time-bin-state parameters such as the symbol rate, pulse separation, and intensity ratio between the signal and decoy states can be easily accessed and changed, allowing the transmitter to adapt to different experimental conditions and contributing to the standardization of QKD implementations.

Stationary optomagnonic entanglement and magnon-to-optics quantum state transfer via opto-magnomechanics

We show how to prepare a steady-state entangled state between magnons and optical photons in an opto-magnomechanical configuration, where a mechanical vibration mode couples to a magnon mode in a ferrimagnet by the dispersive magnetostrictive interaction, and to an optical cavity by the radiation pressure. We find that, by appropriately driving the magnon mode and the cavity to simultaneously activate the magnomechanical Stokes and the optomechanical anti-Stokes scattering, a stationary optomagnonic entangled state can be created. We further show that, by activating the magnomechanical state–swap interaction and subsequently sending a weak red-detuned optical pulse to drive the cavity, the magnonic state can be read out in the cavity output field of the pulse via the mechanical transduction. The demonstrated entanglement and state-readout protocols in such a novel opto-magnomechanical configuration allow us to optically control, prepare, and read out quantum states of collective spin excitations in solids, and provide promising opportunities for the study of quantum magnonics, macroscopic quantum states, and magnonic quantum information processing.

Experimental realization of revival of silenced echo memory protocol in optical cavity

We demonstrated a photon echo quantum memory for weak input optical pulses on the ROSE protocol in a Tm3+:Y3Al5O12 crystal placed in impedance-matched optical cavity. The quantum efficiency of 21% for a storage of time of 36 µs was achieved for single light pulses.

High-fidelity spin measurement on the nitrogen-vacancy center

Nitrogen-vacancy (NV) centers in diamond are versatile candidates for many quantum information processing tasks, ranging from quantum imaging and sensing through to quantum communication and fault-tolerant quantum computers. Critical to almost every potential application is an efficient mechanism for the high fidelity readout of the state of the electronic and nuclear spins. Typically such readout has been achieved through an optically resonant fluorescence measurement, but the presence of decay through a meta-stable state will limit its efficiency to the order of 99%. While this is good enough for many applications, it is insufficient for large scale quantum networks and fault-tolerant computational tasks. Here we explore an alternative approach based on dipole induced transparency (state-dependent reflection) in an NV center cavity QED system, using the most recent knowledge of the NV center’s parameters to determine its feasibility, including the decay channels through the meta-stable subspace and photon ionization. We find that single-shot measurements above fault-tolerant thresholds should be available in the strong coupling regime for a wide range of cavity-center cooperativities, using a majority voting approach utilizing single photon detection. Furthermore, extremely high fidelity measurements are possible using weak optical pulses.

Microwave-assisted arbitrary optical-pulse generation in a thermal vapor

The propagation of a weak optical pulse through an atomic system in closed $\Lambda$ configuration is investigated in which the hyper fine levels are coupled by a microwave pulse. Under three photon resonance condition, it is observed that the probe pulse shape gets cloned by the shape of the microwave pulse along propagation through the medium. The temporal position of the probe pulse is dragged to that of the microwave pulse. A simple expression for the linear susceptibility of the medium for the corresponding transition is derived in the Fourier domain. From the numerical analysis of dynamics using this expression, it is concluded that the novel effect arises from the ground state coherence of the hyper fine transitions induced by the microwave pulse.

Autonomous open-source hardware apparatus for quantum key distribution

We describe an autonomous, fully functional implementation of the BB84 quantum key distribution protocol using open source hardware microcontrollers for the synchronization, communication, key sifting and real-time key generation diagnostics. The quantum bits are prepared in the polarization of weak optical pulses generated with light emitting diodes, and detected using a sole single-photon counter and a temporally multiplexed scheme. The system generates a shared cryptographic key at a rate of 365 bps, with a raw quantum bit error rate of 2.7%. A detailed description of the peripheral electronics for control, driving and communication between stages is released as supplementary material. The device can be built using simple and reliable hardware and it is presented as an alternative for a practical realization of sophisticated, yet accessible quantum key distribution systems.Received: 11 Novembre 2015, Accepted: 7 January 2016; Edited by: O. Martínez; DOI: http://dx.doi.org/10.4279/PIP.080002Cite as: I H López Grande, C T Schmiegelow, M A Larotonda, Papers in Physics 8, 080002 (2016)This paper, by I H López Grande, C T Schmiegelow, M A Larotonda, is licensed under the Creative Commons Attribution License 3.0.

Coherent Spin Control at the Quantum Level in an Ensemble-Based Optical Memory.

Long-lived quantum memories are essential components of a long-standing goal of remote distribution of entanglement in quantum networks. These can be realized by storing the quantum states of light as single-spin excitations in atomic ensembles. However, spin states are often subjected to different dephasing processes that limit the storage time, which in principle could be overcome using spin-echo techniques. Theoretical studies suggest this to be challenging due to unavoidable spontaneous emission noise in ensemble-based quantum memories. Here, we demonstrate spin-echo manipulation of a mean spin excitation of 1 in a large solid-state ensemble, generated through storage of a weak optical pulse. After a storage time of about 1ms we optically read-out the spin excitation with a high signal-to-noise ratio. Our results pave the way for long-duration optical quantum storage using spin-echo techniques for any ensemble-based memory.

An integrated processor for photonic quantum states using a broadband light–matter interface

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 we describe how a broadband waveguide quantum memory based on the atomic frequency comb (AFC) protocol can be used as a programmable processor for essentially arbitrary spectral and temporal manipulations of individual quantum optical pulses. Using weak coherent optical pulses at the few photon level, we experimentally demonstrate sequencing, time-to-frequency multiplexing and demultiplexing, splitting, interfering, temporal and spectral filtering, compressing and stretching as well as selective delaying. Our integrated light–matter interface offers high-rate, robust and easily configurable manipulation of quantum optical pulses and brings fully practical optical quantum devices one step closer to reality. Furthermore, as the AFC protocol is suitable for storage of intense light pulses, our processor may also find applications in classical communications.

Does transmission of a weak optical pulse in a dense absorption medium require quantization of the optical field?

We present an analysis of the transmission of a weak optical pulse, with energy 1ℏω0, through a dense absorbing medium with absorption frequency ω0. We analyze the system by treating the optical pulse classically and the absorbing medium quantum mechanically. We find that the probabilistic back reaction of the quantum absorber on the classical pulse impresses statistical behavior on the pulse that does not arise from quantization of the optical field. All properties of the optical transmission and atomic absorption are self-consistent without contradiction. Issues relating to conservation of energy are resolved by considering the impact of superposition states on conservation laws in individual interactions. As a result, we conclude that transmission of a weak optical pulse with energy 1ℏω0 through a dense atomic absorber does not require quantization of the field.

Nonvolatile bistable all-optical switch from mechanical buckling

We propose a nonvolatile all-optical bistable optomechanical switch comprising two parallel buckling waveguides. The bistability comes from mechanical buckling so the operation of the switch does not require maintenance power. The switching and reading of the states are all optical; they involve relatively strong and relatively weak optical pulses, respectively, similar to conventional bistable optical switches.

Absorption of a pulse by an optically dense medium: An argument for field quantization

The theory of the absorption of a weak optical pulse by an optically dense medium is shown to lead to unphysical results unless the radiation field is quantized. In contrast to the photoelectric effect, the atom-field dynamics for pulsed field absorption can be obtained using elementary quantum mechanics without imposing any assumptions on the nature of the detection process. As such, pulsed field absorption offers distinct advantages over the photoelectric effect as a proving ground for field quantization. If the classical field pulse is replaced by a quantized, multimode field state, many classical field results are recovered without the inconsistencies that arise in the classical field calculation.

On effects of the parametric interaction of extremely short and quasi-monochromatic pulses

The effect of delay and transformation of the frequency of a weak optical pulse upon its nonlinear interaction with an intense extremely short pulse is studied. Reflection from solitons and breathers is considered, and the corresponding conditions for detuning the group velocities and parameters of a medium are formulated.

Storage and Recall of Weak Coherent Optical Pulses with an Efficiency of 25%

We demonstrate experimentally an efficient coherent rephasing scheme for the storage and recall of weak coherent light pulses in an inhomogeneously broadened optical transition in a Pr(3+):YSO crystal at 2.1 K. Precise optical pumping using a frequency stable (≈1 kHz linewidth) laser is employed to create a highly controllable atomic frequency comb structure. We report single photon level storage and retrieval efficiencies of 25%, based on coherent photon-echo-type reemission in the forward direction. The high efficiency is mainly a product of our highly controllable and precise ensemble-shaping technique. The coherence property of the quantum memory is proved through interference between a super-Gaussian pulse and the emitted echo.

Generation of High-Repetition-Rate Pulse Trains through the Continuous-Wave Perturbed by a Weak Gaussian Pulse in an Optical Fiber

A new means of generating all-optically high-repetition-rate pulse trains is proposed and numerically demonstrated in an optical fiber. Our numerical simulations show that, due to the modulation instability effect, the initial continuous-wave with a weak optical pulse instead of conventional weak sinusoidal modulation imposed on it can gradually evolve into high-repetition-rate pulse trains. However, the generated pulse trains take on different features from the conventional case in terms of their widths, intensities, intervals, numbers, and pedestals.

Dynamics of coupled ultraslow optical solitons in a coherent four-state double- ${\sf \Lambda}$ system

We present a systematical investigation, both analytical and numerical, on the dynamics of two nearly lossless and distortion-free weak nonlinear optical pulses in a cold, lifetime-broadened four-state double-Λ system via electromagnetically induced transparency. Starting from the equations of motion of atomic response and probe fields, we give a detail derivation of two coupled nonlinear Schrodinger equations that control the nonlinear evolution of two probe field envelopes by means of a standard method of multiple-scales. We show that stable optical solitons with very slow propagating velocity can be generated under very low input light intensity when working in the transparency window of probe absorption spectrum induced by two continuous-wave control fields. We demonstrate that coupled optical soliton pairs are possible in the system through cross-phase modulational instability and mutual trapping effect of solitons. We provide various coupled optical soliton pair solutions explicitly and analyze their stability numerically.

Realization of a Multiqubit Conditional Phase Gate by Virtue of a Weak Coherent Light Field

We propose a scalable scheme to generate a multiqubit conditional phase gate by using a basic building block, i.e., a weak coherent optical pulse |α〉 reflected successively from a cavity with trapped atoms. In the scheme, we use a coherent state of light instead of a single photon source, homodyne measurement on a coherent light field instead of single photon detection, which reduces the complexity of the practical experiment. The outcomes of these measurements indicate either completion of the gate or the presence of the original qubits such that the operation can be repeated until it is successful.

Homodyne detection of weak coherent optical pulse: Applications to quantum cryptography

AbstractWe propose a quantum key distribution system using balanced homodyne detection, in which strong reference pulses are time‐multiplexed with weak signal pulses by means of fiber interferometer. We use a dual‐threshold decision scheme for postdetection to improve the system performance in terms of BER, with a trade‐off in effective key generation rate. We conduct experimental measurements at 64 km SMF fiber at 1550 nm wavelength, and we prove that the system security can also be enhanced with properly selected threshold parameters. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 1934–1939, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24471

Generation of atomic Greenberger–Horne–Zeilinger states and cluster states through cavity-assisted interaction

This paper proposes a scalable scheme to generate n-atom GHZ states and cluster states by using the basic building block, i.e., a weak coherent optical pulse |α〉 being reflected successively from a single-atom cavity. In the schemes, coherent state of light is used instead of single photon source, homodyne measurement on coherent light is done instead of single photon detection, and no need for individually addressing keeps the schemes easy to implement from the experimental point of view. The successful probabilities of our protocols approach unity in the ideal case.

Subluminal to superluminal propagation of an optical pulse in an f-deformed Bose–Einstein condensate

In this paper, we investigate the propagation of a weak optical probe pulse in an f-deformed Bose–Einstein condensate of a gas with the Λ-type three-level atoms in the electromagnetically induced transparency regime. We use an f-deformed generalization of an effective two-level quantum model of the three-level Λ configuration in which Gardiner's phonon operators for Bose–Einstein condensates are deformed by an operator-valued function, , of the particle-number operator . By making use of the quantum approach of the angular momentum theory, we obtain the eigenvalues and eigenfunctions of the system up to a first-order approximation. We consider the collisions between the atoms as a special kind of f-deformation. The collision rate κ is regarded as the deformation parameter and light propagation in the deformed Bose–Einstein condensate is analysed. In particular, we show that the absorptive and dispersive properties of the deformed condensate can be controlled effectively by changing the deformation parameter κ and the total number of atoms. We find that by increasing the value of κ the group velocity of the probe pulse changes, through deformed condensate, from subluminal to superluminal.