Abstract : Rare-earth ions are useful for the implementation of quantum memory. In particular, the energy levels and magnetic/spin properties of select ions may enable storage of quantum states. Also, the optical activity may enable optical read-out techniques and optical transmission of qubit states. In addition, the energy levels of ions can be used for designing superconducting qubits where the ionic configuration tunes the Hamiltonian for quantum computing. In the more near term, ions embedded in superconductor heterostructure can be used to implement cryogenic memory for superconducting digital computing. Our concept involves embedding rare-earth ions in superconductor devices to provide a low dissipation environment and access to the systems Hamiltonian. In this report we show results and success in integrating rare-earth neodymium by ion implantation in thin films of niobium and niobium-based heterostructure devices. We model the ion implantation process and confirm the concentration of the neodymium in niobium by energy dispersive X-ray (EDX) spectroscopy in a scanning electron microscope (SEM). We study the effect of optical illumination and magnetic stimulus on the transport of the devices at room temperature, as it is important to understand the films and devices so they can properly designed and optimized for utility as quantum memory. We find that the magnetic field has a strong effect on the response. We also find that the selectivity in the optical effect when using a broadband halogen lamp in comparison to a light emitting diode (LED) with selectivity in the excitation wavelength, reinforces the role of the magnetic and optically active Nd rare-earth ions on the device response.
It is known that the opening or closing mechanism of a voltage-gated ion channel is triggered by the potential difference across the cell membrane in the nervous system. Based on this picture, we model the ion channel as a nanoscale two-terminal ionic tunneling junction. We apply an external time-varying voltage on the junction to mimic the membrane potential difference in the stimulation of neurons. We derive the non-Markovian quantum Langevin equation from the first principle of quantum mechanics for the ion transport in ion channels, and obtain the ion transport current in terms of quantum tunnelings of ions controlled by the time-varying voltage. We find that the time-varying voltage induces an effective magnetic flux, which causes quantum coherence in ion tunnelings. This effective magnetic flux induces further an oscillatory component to the spectral structure of the ion system, forming a time-dependent quantum memory. Such voltage-induced memory is defined as the active quantum memory, which manifests in the system with a regular oscillatory sideband structure in the ion transport current. The sideband structure demonstrates a multicrossing hysteresis in the current-voltage ( I − V ) curve, responding to the variation of the time-varying voltage (membrane potential difference). We also find that the strength of active quantum memory can be described by the ratio of amplitude and frequency of the time-varying voltage, and can be quantitatively measured through the number of nonzero cross points in the I − V hysteresis and conductance-voltage diagram. Additionally, we explore the temperature dependence of the active quantum memory in such a system. Further, we apply this model to the ion channel system on the biological energy scale. The description of these active quantum memory characteristics provides a quantum mechanical understanding to the underlying mechanism of ion channel dynamics.
Abstract : This technical report presents simulation and experimental hardware development of pulsed modulated microwave/radio frequency electronic control circuitry for control of electron/nuclear spin states of qubits/quantum memory applicable to semiconductor, superconductor, ionic and superconductor-ionic hybrid technologies. As the pulse quality and need for development of single pulses with very high quality will impact directly the coherence time of the qubit/memory, we present as an example the integration of cryogenic superconductor components including filters and amplifiers to improve the pulse quality and validate the approach. Control of qubits/quantum memory using this technology will be subject of future report.
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.
This paper presents a comprehensive theoretical investigation of quantum information storage via the Higgs amplitude mode in superconductors. We propose a novel quantum memory mechanism based on coherent excitation and echo retrieval of the Higgs mode, exploiting the collective nature of the superconducting condensate. Through rigorous theoretical analysis combining time-dependent Ginzburg-Landau theory with quantum master equations, we demonstrate that Higgs mode excitations can store quantum information with coherence times exceeding 100 ns. We derive analytical expressions for storage fidelity as a function of temperature, gap anisotropy, and disorder, achieving theoretical fidelities above 95% for storage times up to 100 ns in clean s-wave superconductors below. Numerical simulations validate our theoretical predictions and reveal optimal parameter regimes for NbN thin films. Our findings establish fundamental bounds on Higgs-based quantum memory and propose experimental protocols compatible with current THz spectroscopy capabilities. This work opens new directions for exploiting collective modes in quantum technologies.
Cryogenic (cryo) memory devices, designed to operate at/below 4 Kelvin (K) temperature, is a prime enabler of practical quantum computing systems, and superconducting (SC) electronic platforms (Figs. 1(a), (b)) [1]. The state-of-the-art quantum algorithms require many arbitrary rotations which demand a large memory to store program instructions [2]. SC qubits (used in most of the existing quantum computing systems) are highly sensitive to noise and hence, to protect the qubit states from thermal disturbances, they are placed at a few milli-Kelvin (mK) temperature. Furthermore, to preserve the integrity of the quantum states, the SC qubits undergo continuous error correction schemes, requiring extensive memory and bandwidth [2]. Superconducting electronics (SCE) (targeted towards space applications, and high-performance computing) outperforms the conventional CMOS counterparts in terms of speed and energy-efficiency (Fig. 1(c)) [3]. Decades of research efforts have given rise to three major categories (and several sub-variants) of cryo-memories based on SC, non-SC, and hybrid technologies (Fig. 2) [2], [4]–[6]. However, the existing variants suffer from one or more of the following challenges - (i) limited scalability, (ii) process complexity, (iii) bulky peripherals, (iv) array-level interference, (v) volatility, and (vi) speed incompatibility. Therefore, a scalable cryo-memory system remains elusive. To address these existing issues, here, we present a novel cryo-memory system utilizing -(i) the polarization-induced Cooper-pair [7] modulation in a ferroelectric
(FE)superconducting quantum interference device (SQUID) (Fig. 3(a)) [8], and (ii) current controlled
SC↔non−SCswitching in a heater cryotron
(hTron)(Fig. 4) [4]. Discrete prototypes of these devices have been demonstrated recently, but their coupled interactions (which we harness in our work) were never explored before.