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IEEE-NPSS Real-Time Conference

Real-time measurement and adjustment of random phase in frequency-nondegenerate entanglement swapping experiment

Ziru Sang, Xiao Qiang Jiang, Feng Li, Han Zhang, Tianming Zhao, Ge Jin

Published Jun 1, 2012• 3 citations
Publisher

Abstract

In this paper, a circuit module developed for the experiment of the frequency-nondegenerate photons entanglement swapping is reported. The module transfers the random time interval into level from +1 to - 1 voltage to drive an electro-optic modulator (EOM). This experiment, aiming to entangle the frequency-nondegerate photons that never interacted, is an advanced strategy for quantum communication. The key point of the experiment is to realize the time interval real-time measurement, computation and feedback control. A precision TDC is built in a field programmable gate array (FPGA) with 40ps per LSB (a RMS resolution about 20ps). A programmable look-up table is used as computing unit and the delay time of the module is less than 110ns.

DOI
10.1109/rtc.2012.6418183

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In this paper, a circuit module developed for the experiment of the frequency-nondegenerate photons entanglement swapping is reported. The module transfers the random time interval into level from +1 to - 1 voltage to drive an electro-optic modulator (EOM). This experiment, aiming to entangle the frequency-nondegerate photons that never interacted, is an advanced strategy for quantum communication. The key point of the experiment is to realize the time interval real-time measurement, computation and feedback control. A precision TDC is built in a field programmable gate array (FPGA) with 40ps per LSB (a RMS resolution about 20ps). A programmable look-up table is used as computing unit and the delay time of the module is less than 110ns.
In this paper, a dedicated feedback circuit module is designed for an experiment of entanglement swapping with frequency-nondegenerate photons. This experiment, aiming to entangle two frequency-nondegerate photons without prior interaction, is an advanced strategy for quantum communication. The key point of the experiment is to actively compensate a random phase shift originating from the frequency difference. The feedback circuit module has functions of measuring the time intervals, converting the time information to control level codes, and outputting control levels to an electro-optic modulator (EOM). A precision TDC is implemented in a field programmable gate array (FPGA) with 40 ps per LSB ( σRMS is less than 30 ps). A programmable look-up table is used as computing unit. The propagation delay time of the whole circuit module is less than 110 ns.
We introduce our recent photonic quantum information processing experiments using the high-speed electro-optic modulator (EOM) based on a lithium niobate waveguides. First, we demonstrated the frequency shifter for single photons by using an optical single sideband (OSSB) modulator, which is based on the nested configuration of four phase modulators (PMs). By properly setting the RF modulation signal and the bias voltage to each PM, we can suppress unwanted sidebands to realize a frequency shifter that can tune the frequency of single photons with accuracy of an RF synthesizer. Using the OSSB modulator, we eliminated the frequency distinguishability between two single photons whose frequencies were different by 25 GHz, and as a result observed a Hong-Ou- Mandel interference with a visibility exceeding 90%. We also proposed and demonstrated a two-qubit controlled logic gate for time-bin qubits using a two-input, two-output optical switch. The switch enables us to individually perform different functions for two temporal bases as a time-dependent beam splitter, so that we can realize controlled-phase (C-Phase) gate for a time-bin qubit. We showed that the states of two separable single photons were entangled as a result of the C-Phase gate operation. We performed the quantum state tomography to obtain density matrices of the output states from the C-Phase gate for some specific input states, and confirmed that the averaged state fidelity to the pure states was 85%. These results indicate that the EOMs will be a useful tool for realizing advanced photonic quantum communication systems.
Quantum key distribution (QKD) is the most matured application of quantum communication. The time synchronization and system timing jitter are essential to a practical QKD experiment, which can directly influence the quantum bit error rate (QBER) and the final key rate. High precision time-to-digital convertor (TDC) can effectively reduce the system timing jitter, resulting in lower QBER and higher key rate. Here, we introduce a TDC based on a field-programmable gate array (FPGA). Its high resolution of 50 ps, low dead time and large dynamic range can well meet the requirement of the QKD experiment. A free space QKD system setup using the FPGA-based TDC has been built up. The timing precision of the synchronous light and the system timing jitter were tested. The results demonstrate that the FPGA-based TDC could be successfully applied in the QKD experiment.
Quantum key distribution (QKD) is the most matured application of quantum communication. The time synchronization and system timing jitter are essential to a practical QKD experiment, which can directly influence the quantum bit error rate (QBER) and the final key rate. High precision time-to-digital converters (TDCs) can effectively reduce the system timing jitter, resulting in lower QBER and higher key rate. Here, we introduce a TDC based on a field programmable gate array (FPGA). Its high resolution (LSB) of 50 ps with precision (RMS) less than 50 ps, low dead time and large dynamic range can well meet the requirement of the QKD experiment. A free space QKD system setup using the FPGA-based TDC has been assembled. The timing precision of the synchronous light and the system timing jitter were determined. The results demonstrate that the FPGA-based TDC could be successfully applied in the QKD experiment.
Control of quantum signals is very robust design technique and very important in quantum signal processing (QSP). It is not easy in experimentation platforms. Field Programmable Gate Array (FPGA) is using to control very various range of devices in quantum fields through PCs. FPGA needs to run modules of components to communicate and interfacing with the PC, through decode perform commands to direct control of digital hardware’s. If programmer has a real-time control of the FPGA via USB, it can be possible to evaluate design parameters changes in real-time, without reprogramming the FPGA. That makes the proposed design platforms easier for researchers. This paper discusses experiment of control quantum signals by FPGA to control coincidence logic for Quantum Entangled Pair (QEP), that able to measure polarization correlations relationships between photons of the QEP. This FPGA helps to determine detection events at different detectors which can be attributed to a single photon pair. Also to determine the correlation time between two different beams frequencies is extremely accurate according to the delay between the beams, which is very short.
In the context of rapid technological advancements, progress in chip manufacturing technology is propelling electronic devices toward miniaturization and high efficiency at an unprecedented pace. The fundamental principles of quantum mechanics are beginning to play a crucial role in modern electronic devices, providing the foundation for new technological methods and research directions. Optical quantum signal processing, as an important branch of quantum technology, utilizes the quantum properties of photons for information processing and transmission, offering advantages such as high bandwidth, low noise, and strong resistance to interference. However, current optical quantum measurement and control instruments face significant challenges in terms of real-time performance and programming complexity, resulting in reduced data processing efficiency and significantly increased development costs. This study implements a real-time processing algorithm for optical quantum signals on a Field-Programmable Gate Array (FPGA). The algorithm possesses advantages of real-time performance, low power consumption, and high integration. It allows for rapid functionality switching and efficient optical quantum signal processing. The design specifically aims to enhance the signal-to-noise ratio, significantly improving measurement accuracy and reliability. Experimental results indicate that this method substantially enhances the measurement precision and signal-to-noise ratio of optical quantum signals. This research provides an efficient and reliable new method for optical quantum signal processing, laying a solid foundation for further studies in quantum communication, quantum computing, and quantum precision measurement.