Quantum Memory Scheme Research Articles

Optical Memory in a Microfabricated Rubidium Vapor Cell.

Scalability presents a central platform challenge for the components of current quantum network implementations that can be addressed by microfabrication techniques. We demonstrate a high-bandwidth optical memory using a warm alkali atom ensemble in a microfabricated vapor cell compatible with wafer-scale fabrication. By applying an external tesla-order magnetic field, we explore a novel ground-state quantum memory scheme in the hyperfine Paschen-Back regime, where individual optical transitions can be addressed in a Doppler-broadened medium. Working on the ^{87}Rb D_{2} line, where deterministic quantum dot single-photon sources are available, we demonstrate bandwidth-matching with hundreds of megahertz broad light pulses keeping such sources in mind. For a storage time of 80ns we measure an end-to-end efficiency of η_{e2e}^{80 ns}=3.12(17)%, corresponding to an internal efficiency of η_{int}^{0 ns}=24(3)%, while achieving a signal-to-noise ratio of SNR=7.9(8) with coherent pulses at the single-photon level.

Memory and Transduction Prospects for Silicon T Center Devices

The T center, a silicon-native spin-photon interface with telecommunication-band optical transitions and long-lived microwave qubits, offers an appealing new platform for both optical quantum memory and microwave-to-optical telecommunication-band transduction. A wide range of quantum memory and transduction schemes could be implemented withT center ensembles with sufficient optical depth, with advantages and disadvantages that depend sensitively on the ensemble properties. In this work we characterize T center spin ensembles to inform device design. We perform the first T ensemble optical depth measurement and calculate the improvement in center density or resonant optical enhancement required for efficient optical quantum memory. We further demonstrate a coherent microwave interface by coherent population trapping and Autler-Townes splitting. We then determine the most promising microwave and optical quantum memory protocol for such ensembles. By estimating the memory efficiency both in free space and in the presence of a cavity, we show that efficient optical memory is possible with reasonable optical density forecasts. Finally, we formulate a transduction proposal and discuss the achievable efficiency and fidelity.Received 13 September 2022Accepted 13 March 2023DOI:https://doi.org/10.1103/PRXQuantum.4.020308Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasCoherent population trappingElectromagnetically induced transparencyQuantum information with hybrid systemsQuantum information with solid state qubitsQuantum interconnectsQuantum memoriesQuantum networksQuantum repeatersQuantum InformationAtomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics

Integrated Multiresonator Quantum Memory

We develop an integrated efficient multiresonator quantum memory scheme based on a system of three interacting resonators coupled through a common resonator to an external waveguide via switchable coupler. It is shown that high-precision parameter matching based on step-by-step optimization makes it possible to efficiently store the signal field and enables on-demand retrieval of the signal at specified time moments. Possible experimental implementations and practical applications of the proposed quantum memory scheme are discussed.

Tomography of Optical Single-Qubit Quantum Memory

Optical quantum memory is one of the basic elements of quantum information systems. However, the possibilities of its application in such systems sometimes can hardly be estimated by existing methods for its characterization. In this work, the tomography of quantum memory has been implemented as a quantum process in a logical basis. It has been shown that the implemented quantum memory scheme for polarization photon qubits with a high accuracy corresponds to the identity transformation and is promising for application in quantum communication and quantum computing.

High-fidelity quantum gates for OAM single qudits on quantum memory

The application of high-dimensional quantum systems (qudits) in quantum computing and communications seems to be a promising avenue due to the possibility of increasing the amount of information encoded in one physical carrier. In this work, we propose a method for implementing single-qudit gates for qudits based on light modes with orbital angular momentum (OAM). Method for logical qudits encoding, which ensures the quasi-cyclicity of operations, is introduced. Based on the protocol for converting the OAM of light in the Raman quantum memory scheme (Vashukevich et al 2020 Phys. Rev. A 101 033830), we show that the considered gates provide an extremely high level of fidelity of single-qudit transformations. We also compare quantum gates’ properties for systems of different dimensions and find the optimal conditions for carrying out transformations in the protocol under consideration.

Multiresonator Quantum Memory with Switcher

A scheme of multiresonator quantum memory based on a system of four interacting resonators connected through a common resonator to an external carrier by means of switchable coupling has been studied. The parameters of the resonators and the frequency spectrum of the system under study have been optimized using algebraic methods. It has been shown that these parameters allow efficient controlled reversible transfer of information into quantum memory with arbitrarily long storage. Possible applications of the developed scheme for quantum processing have been discussed.

A Noise-Robust Pulse for Excitation Transfer in a Multi-Mode Quantum MemorySupported by the National Natural Science Foundation of China (Grant No. 11974336), and the National Key Research and Development Program of China (Grant No. 2017YFA0304100).

Multi-mode quantum memory is a basic element required for long-distance quantum communication, as well as scalable quantum computation. For on-demand readout and long storage times, control pulses are crucial in order to transfer atomic excitations back and forth into spin excitations. Here, we introduce noise-robust composite pulse sequences for high-fidelity excitation transfer in multi-mode quantum memory. These pulses are robust to the deviations in amplitude and the detuning parameters of realistic conditions. We show the efficiency of these composite pulses with a typical rare-earth ion-doped system. This approach could be applied to a variety of quantum memory schemes.

Conversion and storage of modes with orbital angular momentum in a quantum memory scheme

The paper studies the Raman quantum memory protocol as applied to quantum light with orbital angular momentum. The memory protocol is implemented on an ensemble of three-level cold atoms with the $\Lambda$- configuration of energy levels. The possibility of storing quantum statistics of light with an orbital momentum is analysed in the case when the driving field could be treated as a plane wave. The efficiency analysis shows that examined storage/retrieval processes do not cause the efficiency decreasing compared with the spatial multimode memory protocol considered in [Golubeva et al. 2012]]. We also present an effective transformation of the orbital angular momentum of a quantum field on a memory cell using the driving field with orbital angular momentum.

Superefficient cascade multiresonator quantum memory

We propose a cascade scheme of a superefficient broadband quantum memory consisting of four high-Q ring resonators forming a controllable frequency comb, interacting with long-lived spin systems and a common waveguide. Using the transfer function giving extended matching conditions, the optimization of all spectroscopic parameters of the system for quantum memory in the resonator is carried out. It was shown that our quantum memory scheme does not impose large restrictions on the parameters of losses in resonators and allows the achievement of a super high efficiency ∼99.99% in a wide frequency range.

Single-nitrogen-vacancy-center quantum memory for a superconducting flux qubit mediated by a ferromagnet

We propose a quantum memory scheme to transfer and store the quantum state of a superconducting flux qubit (FQ) into the electron spin of a single nitrogen-vacancy (NV) center in diamond via yttrium iron garnet (YIG), a ferromagnet. Unlike an ensemble of NV centers, the YIG moderator can enhance the effective FQ-NV-center coupling strength without introducing additional appreciable decoherence. We derive the effective interaction between the FQ and the NV center by tracing out the degrees of freedom of the collective mode of the YIG spins. We demonstrate the transfer, storage, and retrieval procedures, taking into account the effects of spontaneous decay and pure dephasing. Using realistic experimental parameters for the FQ, NV center and YIG, we find that a combined transfer, storage, and retrieval fidelity higher than 0.9, with a long storage time of 10 ms, can be achieved. This hybrid system not only acts as a promising quantum memory, but also provides an example of enhanced coupling between various systems through collective degrees of freedom.

Characterization of the hyperfine interaction of the excited D05 state of Eu3+:Y2SiO5

We characterize the Europium (Eu$^{3+}$) hyperfine interaction of the excited state ($^5$D$_0$) and determine its effective spin Hamiltonian parameters for the Zeeman and quadrupole tensors. An optical free induction decay method is used to measure all hyperfine splittings under weak external magnetic field (up to 10 mT) for various field orientations. On the basis of the determined Hamiltonian we discuss the possibility to predict optical transition probabilities between hyperfine levels for the $^7$F$_{0} \longleftrightarrow ^5$D$_{0}$ transition. The obtained results provide necessary information to realize an optical quantum memory scheme which utilizes long spin coherence properties of $^{151}$Eu$^{3+}$:Y$_2$SiO$_5$ material under external magnetic fields

Quantum memory on a charge qubit in an optical microresonator

A quantum-memory unit scheme on the base of a semiconductor structure with quantum dots is proposed. The unit includes a microresonator with single and double quantum dots performing frequencyconverter and charge-qubit functions, respectively. The writing process is carried out in several stages and it is controlled by optical fields of the resonator and laser. It is shown that, to achieve high writing probability, it is necessary to use high-Q resonators and to be able to suppress relaxation processes in quantum dots.

Off-resonant Raman quantum memory in impurity crystals: signal-to-noise ratio analysis

The possibility of implementing an off-resonant Raman scheme of optical quantum memory on the basis of an ensemble of three-level atoms is investigated under the condition of equal polarisations of resonant transitions forming the Λ-scheme. The developed model is used to analyse the signal-to-noise ratio at the output of an optical quantum memory device in 143Nd3+ : Y 7LiF4. It is shown that this ratio can significantly exceed unity for single-photon input pulses. The required values of the parameters can be obtained by using an impurity crystal in the form of a whispering-gallery mode ring resonator.

Photon echo of an ultranarrow optical transition of 167Er3+ in 7LiYF4 crystals

The longitudinal and transverse relaxation times for a transition between hyperfine sublevels of the lower electronic states of the 4I15/2 and 4I9/2 multiplets of 167Er3+ ions in 7LiYF4 crystals have been determined for the first time using two-pulse and stimulated photon echo measurements in zero magnetic field at a temperature of 4 K. The decay of the photon echo signal has been shown to be modulated, which is tentatively attributed to the superhyperfine interaction of the 167Er3+ ions with their 19F− nearest neighbours. The contributions of various types of interaction to the ultranarrow linewidth (~24 MHz) of the transition in question are discussed. Our results demonstrate that this optical transition of the 167Er3+ ion in 7LiYF4 crystals is potentially attractive for use in Raman quantum memory schemes.

A high-fidelity memory scheme for quantum data buses**Project supported by the National Natural Science Foundation of China (Grant Nos. 61673389, 61273202, 61134008, and 11404113).

A novel quantum memory scheme is proposed for quantum data buses in scalable quantum computers by using adjustable interaction. Our investigation focuses on a hybrid quantum system including coupled flux qubits and a nitrogen–vacancy center ensemble. In our scheme, the transmission and storage (retrieval) of quantum state are performed in two separated steps, which can be controlled by adjusting the coupling strength between the computing unit and the quantum memory. The scheme can be used not only to reduce the time of quantum state transmission, but also to increase the robustness of the system with respect to detuning caused by magnetic noises. In comparison with the previous memory scheme, about 80% of the transmission time is saved. Moreover, it is exemplified that in our scheme the fidelity could achieve 0.99 even when there exists detuning, while the one in the previous scheme is 0.75.

Sub-megahertz linewidth single photon source

We report 100% duty cycle generation of sub-MHz single photon pairs at the rubidium D1 line using cavity-enhanced spontaneous parametric downconversion. The temporal intensity cross correlation function exhibits a bandwidth of 666±16 kHz for the single photons, an order of magnitude below the natural linewidth of the target transition. A half-wave plate inside our cavity helps to achieve triple resonance between pump, signal, and idler photon, reducing the bandwidth and simplifying the locking scheme. Additionally, stabilisation of the cavity to the pump frequency enables the 100% duty cycle. The quantum nature of the source is confirmed by the idler-triggered second-order autocorrelation function at τ=0 to be gs,s(2)(0)= 0.016±0.002 for a heralding rate of 5 kHz. The generated photons are well-suited for storage in quantum memory schemes with sub-natural linewidths, such as gradient echo memories.

Cooperative single-photon subradiant states in a three-dimensional atomic array

We propose a complete superradiant and subradiant states that can be manipulated and prepared in a three-dimensional atomic array. These subradiant states can be realized by absorbing a single photon and imprinting the spatially-dependent phases on the atomic system. We find that the collective decay rates and associated cooperative Lamb shifts are highly dependent on the phases we manage to imprint, and the subradiant state of long lifetime can be found for various lattice spacings and atom numbers. We also investigate both optically thin and thick atomic arrays, which can serve for systematic studies of super- and sub-radiance. Our proposal offers an alternative scheme for quantum memory of light in a three-dimensional array of two-level atoms, which is applicable and potentially advantageous in quantum information processing.

Electrically Controlled Quantum Memories With a Cavity and Electro-Mechanical System

In this paper, we propose a scheme to realize electrically controlled quantum memories in a cavity and electro-mechanical system. By assisting with a constant weak optical field into the high- $Q$ cavity, the electrical manipulations of the dark-state polariton and the group velocity of light are derived. The storage and retrieval of the photon state can be realized and optimized by sending the optimal voltage waveforms in the electric circuit, respectively. In addition, the storage efficiency and the experimental feasibility are discussed. The cavity-induced quantum memory scheme driven by the electric field here has potential applications in future integration and miniaturization of optical information processing devices.

Modular quantum memories using passive linear optics and coherent feedback

In this paper, we show that quantum memory for qudit states encoded in a single photon pulsed optical field has a conceptually simple modular realization using only passive linear optics and coherent feedback. We exploit the idea that two decaying optical cavities can be coupled in a coherent feedback configuration to create an internal mode of the coupled system which is isolated and decoherence-free for the purpose of qubit storage. The qubit memory can then be switched between writing/read-out mode and storage mode simply by varying the routing of certain freely propagating optical fields in the network. It is then shown that the qubit memories can be interconnected with one another to form a qudit quantum memory. We explain each of the phase of writing, storage, and read-out for this modular quantum memory scheme. The results point a way towards modular architectures for complex compound quantum memories.

Atomic quantum memory for multimode frequency combs

We propose a Raman quantum memory scheme that uses several atomic ensembles to store and retrieve the multimode highly entangled state of an optical quantum frequency comb, such as the one produced by parametric down-conversion of a pump frequency comb. We analyse the efficiency and the fidelity of such a quantum memory. Results show that our proposal may be helpful to multimode information processing using the different frequency bands of an optical frequency comb.