Abstract Developing the field of neuromorphic quantum computing necessitates designing scalable quantum memory devices. Here, we propose a superconducting quantum memory device in the microwave regime, termed a microwave quantum memcapacitor. It comprises two linked resonators, the primary one is coupled to a Superconducting Quantum Interference Device, which allows for the modulation of the resonator properties through external magnetic flux. The auxiliary resonator, operated through weak measurements, provides feedback to the primary resonator, ensuring stable memory behavior. This device operates with a classical input in one cavity while reading the response in the other, serving as a fundamental building block toward arrays of microwave quantum memcapacitors. We observe that a bipartite setup can retain its memory behavior and gains entanglement and quantum correlations. Our findings pave the way for the experimental implementation of memcapacitive superconducting quantum devices and memory device arrays for neuromorphic quantum computing.
Abstract Developing the field of neuromorphic quantum computing necessitates designing scalable quantum memory devices. Here, we propose a superconducting quantum memory device in the microwave regime, termed a microwave quantum memcapacitor. It comprises two linked resonators, the primary one is coupled to a Superconducting Quantum Interference Device, which allows for the modulation of the resonator properties through external magnetic flux. The auxiliary resonator, operated through weak measurements, provides feedback to the primary resonator, ensuring stable memory behavior. This device operates with a classical input in one cavity while reading the response in the other, serving as a fundamental building block toward arrays of microwave quantum memcapacitors. We observe that a bipartite setup can retain its memory behavior and gains entanglement and quantum correlations. Our findings pave the way for the experimental implementation of memcapacitive superconducting quantum devices and memory device arrays for neuromorphic quantum computing.
Microwave quantum memory represents a critical component for quantum radars and resource-efficient approaches to quantum error correction. Superconducting microwave resonators provide highly efficient storage, long coherence times, on-demand reading, and even memory pulse engineering, but it is still challenging to overcome design and materials induced loss channels for on-chip realization. In this Letter, we present a novel architecture of integrated superconducting quantum memory with a dynamically controlled RF-SQUID coupling element in pulse regime, thus ensuring high efficiency storage and cycling storage time. It demonstrates a memory cycle time of 1.51 μs and 57.5(4)% storage fidelity with preservation of the stored pulse shape during the retrieval at single-photon level excitations. We establish that while the proposed active coupler realization introduces no measurable fidelity degradation, the primary limitation arises from impedance matching and materials imperfections. Still the device was used only for storing finite-duration near-single-photon classical microwave pulses, we assert that it operates as a linear device when the photon population in the common resonator remains low so it should be compatible with quantum state storage. The proposed architecture highlights a disruptive potential for on-chip qubit and memory integration for scalable quantum error correction, while identifying specific avenues for near-unity storage fidelity.
Superconducting circuit quantum electrodynamics is the main architecture for implementation of quantum processors. This work presents a proposal to miniaturize quantum memory devices by combining the quantum memory qubits encoded directly in the first two Fock states ${|0\ensuremath{\rangle},|1\ensuremath{\rangle}}$ and the bus channel in the same specially designed multimode cavity. One key feature of the resonant modes used for quantum memory is that the microwave current is localized, which facilitates the storage and retrieval of information in superconducting qubits while preventing crosstalk from other resonant modes. Frequency design and distinct coupling strengths in this kind of device are analyzed with electromagnetic simulations and numerical calculations. The quantum memory properties, e.g., storage speed, fidelity, and stability, are examined in four cases: (1) memory operation of single-qubit state, (2) disturbing effects, (3) coupling operation, and (4) entangled states storage. Decoherence time of the quantum processor can be extended to more than one order of magnitude longer than that without the memory. By integrating transmons with optimally designed coplanar waveguide multimode quantum memories, the present study could provide an optimistic perspective for the development of large-scale superconducting quantum processors.
Abstract As quantum computing progresses toward large-scale implementation, there is a growing demand for cryo-compatible artificial intelligence hardware and computing paradigms that accelerate the quantum control and error correction. Here, we present a superconducting memory device composed of a flux-quanta storage loop and a superconducting quantum interference device (SQUID), functioning as an artificial synapse and a binary stochastic neuron, respectively. Information is encoded in the stochastic behavior of the pulse stream passing through the neuron and is extracted by counting the number of SQUID switching events. In this scheme, sampling precision is flexibly tunable by adjusting the total number of input pulses. This architecture enables both neuromorphic and probabilistic computing, achieving 100% accuracy in nine-pixel image classification and integer factorization tasks by tuning the sampling precision. Furthermore, we found that the fabrication non-uniformities of up to 7.1% can be effectively compensated by an increased coupling strength. These results highlight the potential of superconducting memory devices as scalable and robust building blocks for implementing versatile AI computing paradigms under cryogenic conditions.
Technology based on memristors, resistors with memory whose resistance depends on the history of the crossing charges, has lately enhanced the classical paradigm of computation with neuromorphic architectures. However, in contrast to the known quantized models of passive circuit elements, such as inductors, capacitors or resistors, the design and realization of a quantum memristor is still missing. Here, we introduce the concept of a quantum memristor as a quantum dissipative device, whose decoherence mechanism is controlled by a continuous-measurement feedback scheme, which accounts for the memory. Indeed, we provide numerical simulations showing that memory effects actually persist in the quantum regime. Our quantization method, specifically designed for superconducting circuits, may be extended to other quantum platforms, allowing for memristor-type constructions in different quantum technologies. The proposed quantum memristor is then a building block for neuromorphic quantum computation and quantum simulations of non-Markovian systems.
We study the entanglement and memristive properties of three coupled quantum memristors. We consider quantum memristors based on conductance-asymmetric superconducting quantum interference device architectures that are coupled via inductors. The three quantum memristors are arranged in two different geometries: linear and triangular coupling configurations. We obtain a variety of correlation measures, including bipartite entanglement and tripartite negativity. For identical quantum memristors, we find that entanglement and memristivity follow the same behavior for the triangular case and the opposite one in the linear case. Finally, we study the multipartite correlations with the tripartite negativity and entanglement monogamy relations, showing that our system has genuine tripartite entanglement. Our results show that quantum correlations in multipartite memristive systems have a nontrivial role and can be used to design quantum memristor arrays for quantum neural networks and neuromorphic quantum computing architectures.
This thesis work deals with a range of superconducting devices operated near the fundamental performance limits set by quantum mechanics along with the nature of quantum vacuum itself when perturbed by such devices. These devices are operated in a dilution refrigerator cooled down to sub-Kelvin temperatures. Low temperature is absolutely essential for quantum behavior of these devices and the minimal inherent noise contribution. Biased, selectively damped superconducting tunnel junction, (also known as the Josephson junction) displaying negative differential resistance, was employed to construct a device capable of amplifying weak microwave signal reflections from it. This device can be operated near the intrinsic precision limits set by the Heisenberg's uncertainty principle. Arrays of Superconducting Quantum Interference Devices (SQUIDs), operated below the critical current, can be used for metamaterial resonators whose resonant frequency can be quickly modulated by magnetic flux. These devices are operated as parametric amplifiers and they are capable of amplifying weak microwave signals near the quantum limit of noise. But more importantly, they are capable of perturbing the vacuum itself, which creates correlated photon pairs seeded by vacuum fluctuations. This effect is known as the dynamical Casimir effect (DCE) and is demonstrated in this thesis work by using power and correlation measurements at microwave frequencies. Furthermore, investigations on the DCE have been extended using a double modulation scheme yielding vacuum-induced coherence and tripartite correlations. Nanocarbon devices have also been studied in this thesis, in particular a wideband low noise nanotube electrometer constructed from a nanotube with proximity induced superconductivity. This device has certain unique benefits when operated in a microwave environment which are discussed in the thesis. Another nanocarbon device, a double quantum dot constructed from graphene and superconducting leads has been used to demonstrate Cooper-pair splitting. This device operates as a tunable source of entangled electrons.