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Technical Physics

Effect of an External Alternating Electric Field on the Efficiency of a Superconducting Single-Photon Detector

К. О. Седых, Е. Сулеймен, М.И. Святодух, A. Podlesnyy, Vadim V. Kovalyuk, Pavel P. An, N. Kaurova, Irina Florya, Kirill Lakhmanskiy, Gregory N Gol'tsman

Published Jun 1, 2024• 0 citations
Publisher

Abstract

Abstract In this paper, model of a surface ion trap for a scalable quantum computer with an RF electrode and a superconducting single-photon detector was studied with an operating temperature of 4 K. The amplitude range of the radio frequency signal varied from 10 to 800 mV at frequencies from 5 to 20 MHz. The effect of the induced external RF field of the trap on the dark and bright count rate of a single-photon detector is studied. The results of this work are important in the design of surface ion traps with planar single-photon detectors.

DOI
10.1134/s1063784224060422

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Abstract In this paper, model of a surface ion trap for a scalable quantum computer with an RF electrode and a superconducting single-photon detector was studied with an operating temperature of 4 K. The amplitude range of the radio frequency signal varied from 10 to 800 mV at frequencies from 5 to 20 MHz. The effect of the induced external RF field of the trap on the dark and bright count rate of a single-photon detector is studied. The results of this work are important in the design of surface ion traps with planar single-photon detectors.
In this paper, model of a surface ion trap for a scalable quantum computer with an RF electrode and a superconducting single-photon detector was studied with an operating temperature of 4K. The amplitude range of the radio frequency signal varied from 10 to 800 mV at frequencies from 5 to 20 MHz. The effect of the induced external RF field of the trap on the dark and bright count rate of a single-photon detector is studied. The results of this work are important in the design of surface ion traps with planar single-photon detectors.
We demonstrate superconducting nanowire single photon detectors with 76 ± 4% system detection efficiency at a wavelength of 315 nm and an operating temperature of 3.2 K, with a background count rate below 1 count per second at saturated detection efficiency. We propose integrating these detectors into planar surface electrode radio-frequency Paul traps for use in trapped ion quantum information processing. We operate detectors integrated into test ion trap structures at 3.8 K both with and without typical radio-frequency trapping electric fields. The trapping fields reduce system detection efficiency by 9%, but do not increase background count rates.
State readout of trapped-ion qubits with trap-integrated detectors can address important challenges for scalable quantum computing, but the strong radio frequency (rf) electric fields used for trapping can impact detector performance. Here, we report on NbTiN superconducting nanowire single-photon detectors (SNSPDs) employing grounded aluminum mirrors as electrical shielding that are integrated into linear surface-electrode rf ion traps. The shielded SNSPDs can be operated at applied rf trapping potentials of up to 54 Vpeak at 70 MHz and temperatures of up to 6 K, with a maximum system detection efficiency of 68%. This performance should be sufficient to enable parallel high-fidelity state readout of a wide range of trapped ion species in a typical cryogenic apparatus.
Trapped-ion qubits are one approach among many for achieving scalable quantum computers. An ion trap has to be operated with several dc and radio frequency (rf) signals to trap and control its qubits. Many ion trap setups are operated at cryogenic temperatures to reduce thermal influences, to reach very high vacuum, and to achieve high fidelity for quantum operations. A resonance circuit, consisting of a coil and the capacitance of the trap electrodes, is used to step-up a low power rf signal to high amplitudes in close proximity to the ion trap. These ac fields are used to confine ions70 μm70 \,{\rm \mu }\mathrm{m}70μmabove a surface ion trap chip. An increased quality factor (Q-factor) of the resonance circuit leads to a higher voltage gain, but the experiment also benefits from a better attenuation of parasitic frequency components in the confining electric field. The Q-factor is inversely proportional to the trap capacitance. Since ion traps are growing in size due to a larger number of qubits, the capacitance is increasing. Therefore, the development of a coil with low losses becomes even more important. In this work, we present the setup of a superconducting coil for a high-Q resonator, measurements of the Q-factor, and its temperature dependency. The coil is made of a niobium-titanium (NbTi) wire wound on a threaded bobbin made of ceramics and equipped with further thermalization structures. The superconducting resonator is a very promising approach to satisfy the needs for future trapped-ion quantum computing setups.
Abstract A superconducting microstrip single-photon detector (SMSPD) generally requires a shunt resistor to avoid latching, caused by its high current-carrying capacity and low kinetic inductance. Here, the effect of the shunt resistor on the behaviors of microbridge SMSPDs was investigated. We analyzed the change in equivalent switching current at different shunt resistances in two ways and determined the operating current range using intrinsic dark count rate (iDCR) curves. We observed that the reduction in shunt resistance can increase the operating current range, which helps to improve the internal detection efficiency (IDE) and reduce the iDCR. However, the reduction in the shunt resistance can reduce the pulse amplitude and increase the pulse decay time, which can degrade the timing jitter and count rate performance of the SMSPD. The trends of the experimental results can be qualitatively reproduced using a circuit model for an SMSPD with a shunt resistor, which provides useful information for the selection of shunt resistors. Furthermore, we report the improved detection performance of a helium-ion-irradiated SMSPD shunted with a small resistance of 5.2 Ω. We observed a weak IDE saturation with a bias current at a wavelength up to 2000 nm and a nonlinear relation between detection current and photon energy.
We report high-fidelity state readout of a trapped ion qubit using a trap-integrated photon detector. We determine the hyperfine qubit state of a single ^{9}Be^{+} ion held in a surface-electrode rf ion trap by counting state-dependent ion fluorescence photons with a superconducting nanowire single-photon detector fabricated into the trap structure. The average readout fidelity is 0.9991(1), with a mean readout duration of 46 μs, and is limited by the polarization impurity of the readout laser beam and by off-resonant optical pumping. Because there are no intervening optical elements between the ion and the detector, we can use the ion fluorescence as a self-calibrated photon source to determine the detector quantum efficiency and its dependence on photon incidence angle and polarization.