Solid-state Quantum Research Articles

Mechanoluminescence and aggregation-enhanced emission (AEE) of an In-MOF based on a 9,9'-diphenyl-9H-fluorene tetraacid linker.

A water-stable In-MOF, constructed based on a conformationally-flexible tetraacid linker, i.e., 2,7-bis(3,5-dicarboxyphenyl)-9,9'-diphenyl-9H-fluorene, i.e., H4DPF, is shown to exhibit a significantly enhanced solid-state fluorescence quantum yield (φf) of 23% in comparison with that of the linker (φfca. 4%) as a consequence of rigidification of the latter by metalation. Application of external stimulus in the form of grinding of the In-MOF leads to a drastic enhancement by 29%, φf from 23 to 52%. Solid-state absorption and emission spectra show that the absorption in the region of 368-550 nm gets diminished with a concomitant change in the emission maximum with a blue shift upon grinding. Fluorescence enhancement with grinding is correlated with a gradual reduction in the size of the particles, as established by SEM analysis. MOF particle aggregation has been invoked to account for the observed fluorescence enhancement in addition to a subtle conformational change in the structure of the linker upon grinding. Intriguingly, the ground MOF particles exhibit aggregation behaviour in the DMF-water solvent system with the emission further increasing up to 75% for the increase in the water fraction (fw) from 0 to 60%; hydrophobic aggregation of particles evidently leads to a change in the conformation of the linker and particle aggregation-enhanced emission (AEE). De-aggregation of particles ensues for fw = 70-90%, as reflected by a gradual decrease in the emission intensity. It is shown that the suspension of ground In-MOF particles in water permits sensing of metal ions, in particular Al3+ ions, by fluorescence quenching with detection at a sub-ppb level. The observed results comprise first demonstration of both mechanoluminescence and AEE of MOF particles.

Carbon Nanodots With Nearly Unity Fluorescent Efficiency Realized via Localized Excitons

Carbon nanodots (CDs) have emerged as an alternative option for traditional nanocrystals due to their excellent optical properties and low toxicity. Nevertheless, high emission efficiency has been a long-lasting pursuit for CDs. Herein, CDs with near-unity emission efficiency have been prepared via atomic condensation of doped pyrrolic nitrogen, which can highly localize the excited states thus lead to the formation of bound excitons and the symmetry break of the π–electron conjugation. The short radiative lifetimes (< 8 ns) and diffusion lengths (< 50 nm) of the CDs imply excitons can be efficiently localized by radiative recombination centers for a defect-insensitive emission of CDs. By incorporating the CDs into polystyrene, flexible light-converting films with high solid state quantum efficiency of 84% and good resistance to water, heating, and UV light have been obtained. With the CD-polymer films as light conversion layer, CD based white light-emitting diodes (WLEDs) with a luminous efficiency of 140 lm W–1 and flat panel illumination system with lighting sizes of more than 100 cm2 have been achieved, matching state-of-the-art nanocrystal-based LEDs. These results pave the way towards carbon-based luminescent materials for solid state lighting technology.

Single Ion Implantation of Bismuth

Ion Implantation In article number 2000237 by Nathan Cassidy, Roger Webb, David Cox, and co-workers, preliminary results are presented from the first commercially produced implanter specifically designed for rapid and precise positioning of single ions into device structures for solid state quantum technology applications. Specifically the implantation of single bismuth ions into Si, Ge, Cu, and Au are reported, and the counting detection efficiency for single ion implants and the factors that affect such detection efficiencies are determined.

Rigidochromism by imide functionalisation of an aminomaleimide fluorophore.

Fluorescent dyes that exhibit high solid state quantum yields and sensitivity to the mechanical properties of their local environment are useful for a wide variety of applications, but are limited in chemical diversity. We report a trityl-functionalised maleimide that displays rigidochromic behaviour, becoming highly fluorescent when immobilised in a solid matrix, while displaying negligible fluorescence in solution. Furthermore, the dye's quantum yield is shown to be sensitive to the nature of the surrounding matrix. Computational studies reveal that this behaviour arises from the precise tuning of inter- and intramolecular noncovalent interactions. This work expands the diversity of molecules exhibiting solid state environment sensitivity, and provides important fundamental insights into their design.

Research progress of silicon and germanium quantum computing materials

Semiconductor quantum dot is one of the promising ways to realize solid-state quantum computing. The key is to obtain high-quality semiconductor quantum computing materials. Silicon and germanium can be isotopically purified to achieve nuclear spin-free isotopes, meeting the requirement for long decoherence time. They are also compatible with the current CMOS technology, thus making them ideal material platforms for large scale integration. This review first summarizes the important progress of semiconductor quantum-dot quantum computing in recent years, then focuses on the material progress including the silicon-based Si/SiGe heterostructures, Ge/SiGe heterostructures, and Ge/Si one-dimensional wires, finally presents the outlook about the development of silicon and Ge quantum computing materials.

Atomic frequency comb optical memory in EuCl&lt;sub&gt;3&lt;/sub&gt;·6H&lt;sub&gt;2&lt;/sub&gt;O crystal

Quantum memory is a crucial component for the large-scale quantum networks. Rare-earth-ion doped crystals have been a promising candidate for the practical quantum memory because of its very long coherence time. However, doped ions cause unwanted lattice distortion, and consequently reduce the optical depth and the storage efficiency. The stoichiometric rare-earth crystals have low lattice distortion and high rare earth ion density, and thus are expected to enable high-efficiency storage. EuCl&lt;sub&gt;3&lt;/sub&gt;·6H&lt;sub&gt;2&lt;/sub&gt;O is a promising material for quantum memory applications because its optical inhomogeneous broadening can be smaller than its hyperfine splitting and the theoretically predicted spin coherence time is up to 1000 seconds. Despite the numerous efforts in solid-state quantum memory based on rare-earth ion doped crystals, optical memory and quantum memory have not been implemented with stoichiometric rare-earth crystals yet. Here, we report the atom frequency comb optical storage using a EuCl&lt;sub&gt;3&lt;/sub&gt;·6H&lt;sub&gt;2&lt;/sub&gt;O crystal. A coherence time of 55.7 μs is obtained by photon echo measurements on &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$^7{\rm{F}}_0 \rightarrow {}^5{\rm{D}}_0$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210648_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210648_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; transition. The two-level atomic frequency comb storage is demonstrated with a storage efficiency of 1.71% at a storage time of 1 μs, showing the potential capability of optical quantum storage of this material. Based on the analysis of the line shift of &lt;inline-formula&gt;&lt;tex-math id="M3"&gt;\begin{document}$^7{\rm{F}}_0 \rightarrow {}^5{\rm{D}}_0$\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210648_M3.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="16-20210648_M3.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; depending on the sample temperature, we highlight the challenge of achieving high-efficiency optical pumping in this material, which imposes a limit on the achievable efficiency.

Digital quantum simulation of Floquet topological phases with a solid-state quantum simulator

Harnessing the dynamics of complex quantum systems is an area of much interest and a quantum simulator has emerged as a promising platform to probe exotic topological phases. Since the flexibility offered by various controllable quantum systems has helped gain insight into the quantum simulation of such complicated problems, an analog quantum simulator has recently shown its feasibility to tackle the problems of exploring topological phases. However, digital quantum simulation and the detection of topological phases still remain elusive. Here, we develop and experimentally realize the digital quantum simulation of topological phases with a solid-state quantum simulator at room temperature. Distinct from previous works dealing with static topological phases, the topological phases emulated here are Floquet topological phases. Furthermore, we also illustrate the procedure of digitally simulating a quantum quench and observing the nonequilibrium dynamics of Floquet topological phases. Using a quantum quench, the 0- and π -energy topological invariants are unambiguously detected through measuring time-averaged spin polarizations. We believe our experiment opens up a new avenue to digitally simulate and detect Floquet topological phases with fast-developed programmable quantum simulators.

Teleportation Systems Toward a Quantum Internet

Quantum teleportation is essential for many quantum information technologies including long-distance quantum networks. Using fiber-coupled devices, including state-of-the-art low-noise superconducting nanowire single photon detectors and off-the-shelf optics, we achieve quantum teleportation of time-bin qubits at the telecommunication wavelength of 1536.5 nm. We measure teleportation fidelities of >=90% that are consistent with an analytical model of our system, which includes realistic imperfections. To demonstrate the compatibility of our setup with deployed quantum networks, we teleport qubits over 22 km of single-mode fiber while transmitting qubits over an additional 22 km of fiber. Our systems, which are compatible with emerging solid-state quantum devices, provide a realistic foundation for a high-fidelity quantum internet with practical devices.

Testing the quantization of electromagnetic field in a quarter-wavelength transmission line resonator by traveling-wave scattering measurements

A half-wavelength cavity, wherein the electromagnetic field is quantized as standing-wave photons, is a typical artificial quantum system that has widely been used to implement quantum information processing. In this paper, we propose an approach to confirm the quantization of the electromagnetic field in another type of cavity, namely, a quarter-wavelength transmission line resonator (TLR), by using traveling-photon scattering measurements. Furthermore, we show that the number of photons in a TLR can be destructively detected by using the usual IQ-mixed technique. We hope that quarter-wavelength TLRs may also serve as quantum devices to implement on-chip solid-state quantum information processing.

Parabolic Diamond Scanning Probes for Single-Spin Magnetic Field Imaging

Enhancing the measurement signal from solid state quantum sensors such as the nitrogen-vacancy (NV) center in diamond is an important problem for sensing and imaging of condensed matter systems. Here we engineer diamond scanning probes with a truncated parabolic profile that optimizes the photonic signal from single embedded NV centers, forming a high-sensitivity probe for nanoscale magnetic field imaging. We develop a scalable fabrication procedure based on dry etching with a flowable oxide mask to reliably produce a controlled tip curvature. The resulting parabolic tip shape yields a median saturation count rate of 2.1 $\pm$ 0.2 MHz, the highest reported for single NVs in scanning probes to date. Furthermore, the structures operate across the full NV photoluminescence spectrum, emitting into a numerical aperture of 0.46 and the end-facet of the truncated tip, located near the focus of the parabola, allows for small NV-sample spacings and nanoscale imaging. We demonstrate the excellent properties of these diamond scanning probes by imaging ferromagnetic stripes with a spatial resolution better than 50 nm. Our results mark a 5-fold improvement in measurement signal over the state-of-the art in scanning-probe based NV sensors.

Manipulation of Spin Polarization Using NV Ensemble in Diamond for Precision Displacement Detection With an Adjustable Sensitivity

Magnetic sensing based on nitrogen-vacancy (NV) centers in diamond have been considered by scientists to be a promising candidate for highly sensitive, integrated solid-state quantum sensors. In this paper, a displacement detection system is presented relying on the quantum magnetic effect of NV ensemble under a microwave (MW), which consists of a fluorescence microscope system and a bundle of movable current-carrying coils. The fluorescence microscope system is responsible for efficient fluorescence excitation and collection to identify the energy level splitting of electron spin. Moreover, the current-carrying coils are responsible for creating a gradient magnetic field with high linearity. Measurement by experiment, the theory sensitivity limit of the proposed device can up to 2.713 nm/Hz1/2, and the noise sensitivity is $51.93~\mu \text{m}$ /Hz1/2 when the coils carry the current 0.1 A. The response of fluorescence intensity (PL) to displacement can be up to 0.493%/mm for $\vert + 1\rangle $ sublevel with a measurement range of 12.57 mm and 0.419%/mm for $\vert - 1\rangle $ sublevel with a measurement range of 13 mm. Through experimental verification, the sensitivity and response can increase proportionally with the current, while the measurement range is inversely reduced. In view of this, the proposed displacement detection system can be used in displacement detection applications of different precision.

High-Fidelity and Robust Geometric Quantum Gates that Outperform Dynamical Ones

Geometric phase is a promising element to induce high-fidelity and robust quantum operations due to its built-in noise-resilience feature. Unfortunately, its practical applications are usually circumscribed by requiring complex interactions among multiple levels/qubits and the longer gate-time than the corresponding dynamical ones. Here, we propose a general framework of geometric quantum computation with the integration of the time-optimal control technique, where the shortest smooth geometric path is found to realize accelerated geometric quantum gates, and thus greatly decreases the gate errors induced by both the decoherence effect and operational imperfections. Meanwhile, we faithfully implement our idea on a scalable platform of a two-dimensional superconducting transmon-qubit lattice, with simple and experimental accessible interactions. In addition, numerical simulations show that our implemented geometric gates possess higher fidelities and stronger robustness, which outperform the best performance of the corresponding dynamical ones. Therefore, our scheme provides a promising alternative way towards scalable fault-tolerant solid-state quantum computation.

Suppression of decoherence tied to electron-phonon coupling in telecom-compatible quantum dots: low-threshold reappearance regime for quantum state inversion.

We demonstrate suppression of dephasing tied to deformation potential coupling of confined electrons to longitudinal acoustic (LA) phonons in optical control experiments on large semiconductor quantum dots (QDs) with emission compatible with the low-dispersion telecommunications band at 1.3 µm. By exploiting the sensitivity of the electron-phonon spectral density to the size and shape of the QD, we demonstrate a fourfold reduction in the threshold pulse area required to enter the decoupled regime for exciton inversion using adiabatic rapid passage (ARP). Our calculations of the quantum state dynamics indicate that the symmetry of the QD wave function provides an additional means to engineer the electron-phonon interaction. Our findings will support the development of solid-state quantum emitters in future distributed quantum networks using semiconductor QDs.

Recent Progress on Ultrathin Metalenses for Flat Optics.

SummaryAs technology advances, electrical devices such as smartphones have become more and more compact, leading to a demand for the continuous miniaturization of optical components. Metalenses, ultrathin flat optical elements composed of metasurfaces consisting of arrays of subwavelength optical antennas, provide a method of meeting those requirements. Moreover, metalenses have many other distinctive advantages including aberration correction, active tunability, and semi-transparency, compared to their conventional refractive and diffractive counterparts. Therefore, over the last decade, great effort has been focused on developing metalenses to investigate and broaden the capabilities of metalenses for integration into future applications. Here, we discuss recent progress on metalenses including their basic design principles and notable characteristics such as aberration correction, tunability, and multifunctionality.

Engineered spin-orbit interactions in LaAlO3/SrTiO3-based 1D serpentine electron waveguides.

The quest to understand, design, and synthesize new forms of quantum matter guides much of contemporary research in condensed matter physics. One-dimensional (1D) electronic systems form the basis for some of the most interesting and exotic phases of quantum matter. Here, we describe a family of quasi-1D nanostructures, based on LaAlO3/SrTiO3 electron waveguides, in which a sinusoidal transverse spatial modulation is imposed. These devices display unique dispersive features in the subband spectra, namely, a sizeable shift (∼7 T) in the spin-dependent subband minima, and fractional conductance plateaus. The first property can be understood as an engineered spin-orbit interaction associated with the periodic acceleration of electrons as they undulate through the nanowire (ballistically), while the second property signifies the presence of enhanced electron-electron scattering in this system. The ability to engineer these interactions in quantum wires contributes to the tool set of a 1D solid-state quantum simulation platform.

Single-electron emission from degenerate quantum levels

Single-electron sources on-demand are requisite for a promising fully electronic platform for solid-state quantum information processing. Most of the experimentally realized sources use the fact that only one electron can be taken from a singly occupied quantum level. Here I take the next step and discuss emission from orbitally degenerate quantum levels that arise, for example, in quantum dots with a nontrivial ring topology. I show that degeneracy provides additional flexibility for single- and two-electron emission. Indeed, the small Aharonov-Bohm flux, which slightly lifts the degeneracy, is a powerful tool for changing the relative width of the emitted wave packets over a wide range. In a ring with one lead, even electrons emitted from completely degenerate levels can be separated in time if the driving potential changes at the appropriate rate. In a ring with two leads, electrons can be emitted to different leads if one of the leads has a bound state with Fermi energy at its end.

Studies on the Coherence Time of the Electron Weakly Coupled with Phonons in Asymmetrical Semi-exponential Quantum Well by Employing Linear Combination Operation Method

We investigate theoretically the properties of the coherence time of a symmetric semi-exponential quantum well qubit using the linear combination operator method for the first time. We derive the influences of quantum well barrier height and the range of an asymmetrical semi-exponential confinement potential (ASECP) on the vibration frequency, first excited-state (FES) energy, excitation energy and coherence time using unitary transformations and Fermi’s Golden Rule. We find that the vibration frequency, FES energy and excitation energy are increasing functions of the barrier height, but are decreasing ones of the ASECP range; the coherence time, however, has totally opposite properties. Our results may be useful for the design and implementation of solid-state quantum computation.

3D Tb(III) and Eu(III) coordination polymers with mixed dicarboxylate ligands: Synthesis, structure and luminescence properties

Coordination polymers [Ln(bta)0.5(ox)0.5(H2O)2]·2H2O (Ln = Tb (1), Eu (2), H2ox = oxalic acid; H4bta = 1,2,4,5-benzenetetracarboxylic acid) were hydrothermally synthesized, and characterized by elemental analysis, IR, TG, XRD as well as single-crystal X-ray diffraction. Coordination polymers 1–2 display three-dimensional (3D) network structures, which can be simplified into a 3D network with topology symbol of {412·63}, and the topology type is pcu. The luminescence properties of 1 and 2 show characteristic emission of Tb(III) and Eu(III) ions, respectively. The solid-state quantum yield Фtotal is 19.96 ± 2.00% and 6.84 ± 0.68% while the fluorescence decay lifetime is τ = 560.2990 μs and τ = 233.8299 μs for 1 and 2, respectively.

Magnetically controllable transmission spectrum of a 1D photonic crystal with a graphene defect layer in infrared region

Magneto-optical properties of a one-dimensional (1D) photonic crystal with a graphene defect layer is investigated. It is shown that the steady-state behavior of the medium completely depends on the intensities of magnetic and coherent coupling fields. By proper chose of the controllable parameters, it is found that the absorption spectrum of 1D photonic crystal can be adjusted easily. In addition, by controlling the magnetic field and Rabi-frequencies of applied lights, the transmitted and reflected light pulses at the infrared region can be tuned. The effect of magnetic and coupling fields on the transmission and reflection properties of the laser pulse at $$\lambda_{0} = 9\;\upmu\hbox{m}$$ of the medium is also studied. It is found that optical bistability in reflection and output fields can be controlled by applying the magnetic and coupling fields. The proposed model may provide some new possibilities for technological applications in optoelectronics, solid-state quantum information science and systems, due to vast applications in signal processing.

Planarized spatially-regular arrays of spectrally uniform single quantum dots as on-chip single photon sources for quantum optical circuits

A long standing obstacle to realizing highly sought on-chip monolithic solid state quantum optical circuits has been the lack of a starting platform comprising scalable spatially ordered and spectrally uniform on-demand single photon sources (SPSs) buried under a planar surface. In this paper, we report on the first realization of planarized SPS arrays based on a unique class of shape-controlled single quantum dots (SQDs) synthesized on mesa top (dubbed MTSQDs) using substrate-encoded size-reducing epitaxy (SESRE) on spatially regular arrays of patterned nanomesas with edge orientation chosen to drive symmetric adatom migration from the nanomesa sidewalls to the top, thereby enabling spatially selective growth. Specifically, on GaAs(001) square nanomesas with edges along ⟨100⟩, we synthesized binary GaAs/InAs/GaAs MTSQDs emitting around 1120 nm with 1.8 nm standard deviation and single photon emission purity &amp;gt;99.5%. SESRE based MTSQDs are shown for the first time to lend themselves to planarization of the surface morphology when grown on pedestal shape mesas. We demonstrate that the planarizing overgrowth process over arrays of InGaAs SQDs largely maintains the SQDs’ high single photon emission purity (&amp;gt;98%) and spectral uniformity (∼5 nm). Such planarized SQD arrays offer the long-sought platform for on-chip integration with light manipulating structures to realize quantum optical circuits.