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arXiv:2006.01823 · Science

Parallel single-shot measurement and coherent control of solid-state spins below the diffraction limit

Songtao Chen, Mouktik Raha, Christopher M. Phenicie, Salim Ourari, Jeff D. Thompson

Published Oct 29, 2020• 141 citations
arXivHTMLPDF

Abstract

Addressing the many and the individual The ability to coherently manipulate the quantum state of atomic defects in solid-state systems is a promising route to developing a platform for quantum technologies. A successful platform requires the interaction of many qubits in close proximity, as well as the ability to address each qubit individually, and, to date, such requirements have run counter to each other. Chen et al. devised an optical frequency-domain method with which they were able to simultaneously address many individual rare-earth ion defects (six at this point) with separations all within the diffraction limit of the control light. Because the approach is scalable to tens or hundreds of defects, it provides the prospect of realizing truly large-scale quantum processors. Science , this issue p. 592

DOI
10.1126/science.abc7821

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Addressing the many and the individual The ability to coherently manipulate the quantum state of atomic defects in solid-state systems is a promising route to developing a platform for quantum technologies. A successful platform requires the interaction of many qubits in close proximity, as well as the ability to address each qubit individually, and, to date, such requirements have run counter to each other. Chen et al. devised an optical frequency-domain method with which they were able to simultaneously address many individual rare-earth ion defects (six at this point) with separations all within the diffraction limit of the control light. Because the approach is scalable to tens or hundreds of defects, it provides the prospect of realizing truly large-scale quantum processors. Science , this issue p. 592
Quantum Systems The ability to coherently manipulate the quantum state of atomic defects in solid-state systems is a promising route to developing a platform for quantum technologies. A successful platform requires the interaction of many qubits in close proximity, as well as the ability to address each qubit individually, and, to date, such requirements have run counter to each other. Chen et al. devised an optical frequency-domain method with which they were able to simultaneously address many individual rare-earth ion defects (six at this point) with separations all within the diffraction limit of the control light. Because the approach is scalable to tens or hundreds of defects, it provides the prospect of realizing truly large-scale quantum processors. Science , this issue p. [592][1] [1]: /lookup/doi/10.1126/science.abc7821
The exploitation of quantum mechanics has the potential to solve important challenges and \nintroduce novel technologies enabling, among others, powerful computation (which can solve \ncertain problems exponentially faster than classical computers), perfectly secure communications, \nas well as sensing and imaging with precision and resolutions not achievable by classical means. \nIn order to make use of the unique properties of quantum physics, experimental platforms \nthat provide access to, and allow the control of quantum states, need to be developed. In \nparticular, quantum systems composed of multiple parties are required, where each party is in a \ncoherent superposition of states, and where multiples of such parties are in a coherent \nsuperposition with each other (e.g. being entangled). Additionally, in order to make use of such \nentangled quantum systems, it is required that each individual party can be coherently controlled \nand measured. The usability and available quantum resources of the entangled system is related \nto its size, which is proportional to the number of entangled parties, as well as the dimensionality \nof the superposition each party is in. For this reason, there is a imminent demand to achieve, \ninvestigate, and improve the generation and control of large quantum systems, comprised of as \nmany entangled parties as possible, where each party is in an ideally high-dimensional \nsuperposition. \nMany quantum platforms are currently subject to extensive research, such as trapped ions, \nsuperconducting circuits, defect centers in solid-state crystals, mechanical oscillators, and optical \nquantum states (i.e. photons). While all platforms provide distinct advantages (as well as \nchallenges), optical photon states are of particular interest, because they can interact with other \nquantum systems, and can be transmitted over long distances while preserving their quantum \ncoherence without the need for extensive shielding. A large variety of sources for optical \nquantum states has been demonstrated, however most such implementations suffer from high \ncomplexity, ultimately limiting their scalability. Integrated photonics has recently become a \nleading platform for the compact, cost-efficient, and stable generation and processing of optical \nquantum states. However, to date, integrated quantum sources have only been able to generate \nphoton pairs, which operated on single channels, and single polarization modes. Furthermore, in \nthe few realizations of on-chip entanglement, they were limited to two entangled parties, where \neach party was in a two-dimensional superposition. These limitations of current integrated photon sources arise in large part from the concepts currently exploited to generate and control these \nstates. In particular, path-entangled sources are the most commonly used, but increasing the \nquantum state complexity requires a significant, and very challenging, increase in device \ncomplexity. There is therefore an urgent need to develop new concepts that can achieve the onchip \ngeneration of large and complex photon states without increasing source complexity, while \nstill enabling coherent quantum state control and detection. \nIn this work, we aim to address these limitations by making use of multiple frequency and \ntemporal modes within a single spatial waveguide mode (therefore readily compatible with \nstandard optical fibers) of an on-chip microring resonator. This approach is in contrast to more \ncommonly used techniques relying on path entanglement, which exploits multiple spatial modes \nand generates entanglement by means of complex waveguide structures. Working within a single \nspatial mode, we achieve the first demonstration of pure heralded single photons and entangled \nphoton pairs, which are emitted on multiple frequency modes from a single source. We then \ndemonstrate the first generation of multi-photon entangled quantum states on a photonic chip. \nFinally, by making use of the spectral multi-mode nature of optical frequency combs, we achieve \nthe generation of photon pairs in a coherent superposition of multiple frequency modes, \nrepresenting the first generation of high-dimensional entangled states on a photonic chip. \nOur work represents a significant step forward in the generation of complex quantum \nstates on a photonic chip and in a single spatial mode compatible with standard optical fibers. In \naddition, we demonstrated coherent quantum state control and manipulation for all generated \nstates by means of standard telecommunications components, which could in the future be also \nintegrated on single, monolithic chip. Our results indicate that the exploitation of integrated \noptical frequency comb sources for the generation of optical quantum states can provide a \nscalable and practical platform for quantum technologies.
The ability to control the state of individual atoms is a new challenge for science and technology in the 21st century. Currently, experiments on individual quantum systems such as trapped ions, single molecules, quantum dots, superconducting qubits and photons are crucial for the rapidly growing field of quantum information processing and communication. In general, solid state systems are preferable for scaling and the choice of material plays a crucial role; for example, in classical electronic devices continual performance enhancement and miniaturization is strongly linked to the success of silicon-based technology. For quantum applications, diamond has the potential to become the material of choice, because its large bandgap enables the control of optically active impurities and higher operation temperature. This focus issue collates original research contributions from some of the leading groups in the field as a showcase for the very latest developments in diamond-based quantum technologies.
The ability to coherently control and read out qubits with long coherence times in a scalable system is a crucial requirement for any quantum processor. Nuclear spins in the solid state have shown great promise as long-lived qubits. Control and readout of individual nuclear spin qubit registers has made major progress in the recent years using individual electron spin ancilla addressed either electrically or optically. Here, we present a new platform for quantum information processing, consisting of 183^{183}183W nuclear spin qubits adjacent to an Er3+^{3+}3+ impurity in a CaWO4_44​ crystal, interfaced via a superconducting resonator and detected using a microwave photon counter at 10mK. We study two nuclear spin qubits with T2∗T_2^*T2∗​ of 0.8(2) 0.8(2)~0.8(2) s and 1.2(3) 1.2(3)~1.2(3) s, T2T_2T2​ of 3.4(4) 3.4(4)~3.4(4) s and 4.4(6) 4.4(6)~4.4(6)  s, respectively. We demonstrate single-shot quantum non-demolition readout of each nuclear spin qubit using the Er3+^{3+}3+ spin as an ancilla. We introduce a new scheme for all-microwave single- and two-qubit gates, based on stimulated Raman driving of the coupled electron-nuclear spin system. We realize single- and two-qubit gates on a timescale of a few milliseconds, and prepare a decoherence-protected Bell state with 88% fidelity and T2∗T_2^*T2∗​ of 1.7(2) 1.7(2)~1.7(2) s. Our results are a proof-of-principle demonstrating the potential of solid-state nuclear spin qubits as a promising platform for quantum information processing. With the potential to scale to tens or hundreds of qubits, this platform has prospects for the development of scalable quantum processors with long-lived qubits.
Ultracold atoms in optical lattices have proven to provide an extremely clean and controlled setting to explore quantum many-body phases of matter. Now, imaging of atoms in such lattice structures has reached the level of single-atom sensitive detection combined with the highest resolution down to the level of individual lattice sites. This has opened up fundamentally new opportunities for the characterization and the control of quantum many-body systems. Here we give a brief overview of this field and explore the opportunities offered for future research.
The proximity between the ions results in large interactions and potentially allows fast gates, but they can still be separately addressed since different ions have different optical resonance frequency. The interaction that enables multi-qubit gates can be turned on at will and is based on that the permanent dipole moment changes as a control ion is transferred to the optically excited state which in turn Stark-shifts target qubit out of resonance. Using optical pumping, all ions within a frequency interval can be removed and then a peak of equivalent ions, each belonging to one instance of many parallel quantum computers can be positioned within the non-absorbing region. This qubit has then been efficiently transferred between different qubit states using robust complex hyperbolic secant pulses. Pairs of qubits that interact strongly have also been distilled