Research On Room Temperature Electronics Readout System For Superconducting Quantum Computing

As two of the most significant applications of the quantum information science,distinguishing quantum information science from the traditional information technol-ogy,quantum computing and quantum communication not only have proven the valid-ity of the quantum mechanics,but also give an expansion of vision to the traditional information technology.As the interdisciplinary studies,they have extraordinary ad-vantages over the classic methods in some specific application scenarios.Taking the“artificial qubit”-Josephson junction as the core components,the superconducting quantum computing system has made great achievement in the quan-tum computing competition stage in recent years,for its characteristics of low noise,high integration,excellent coherence and other comparative advantages.And it wins the attention and continuous investment from magnates such as Google,IBM,Intel and etc.China',s first on-line quantum computer is also developed basing on supercon-ducting quantum computing system.However,most of the reported demonstrations of quantum algorithms fall in the category of open-loop static quantum circuits,which are characterized by applying a series of manipulation gate sequences on the quantum bits,followed by the measurement as the end step.But it's not enough for the scaled quantum computer.For reasons,the phenomenon of energy relexation and dephasing make the decoherence of the quibit,and the qubits in ground state will also be thermally excited to the excited state randomly.This natural decoherence and thermal excitation process will bring the born-with bit error rate to the quantum computing.Only by implement-ing the key algorithms like quantum error correction and active reset,and advancing the emergence of fault-tolerant quantum computing,the realization of scaled quantum computer turns possible.All of mentioned above raise a requirement for closed-loop feedback in real time,making it possible to adjust the gate sequence conditioned on the projective measurement.For the aspect of quantum computing,what mainly described in this thesis are as follows:for the requirement of building scaled superconducting quantum computers,the room temperature electronic readout system suitable for quantum computing system is originally designed and implemented.The system is capable to acquisit the IF(Inter-mediate Frequency)readout pulse with a high sample rate of 1 Gsps,and accomplish a series of pipeline posting-process for up to 8 qubit with a delay of 184 nanosecond,including parallel demodulation,quantum state analysis and the quantum state transmis-sion.Compared with most of domestic groups relying on the commercial high-speed acquisiton cards for relevant experiments,the application of the system not only greatly improves the integration of superconducting quantum computing experimental equip-ment,improving the number of qubit that can be read at one time during the experiment,but also replaces the original offline processing of the quantum state by hardware real-time processing,which shortens the experimental time and increases the efficiency of the experiment.Through continuous working within multiple quantum computers for over two years,it has been fully proven that the electronic readout system is robust enough to support the long-term stable operation of static quantum circuits.For the demand in building a scaled quantum computer,cooperating with the self-developed arbitrary wave generator,a closed loop of dynamic quantum feedback can be performed by the electronics readout system within 600 nanoseconds.This loop includes a series of operation:sampling for 100 nanoseconds,demodulation,state de-termination,state broadcas and generating the control gate conditioned on the measure-ment.With the dynamic quantum feedback loop,a series of complex quantum algo-rithm is demonstrated including active reset.To our knowledge,it is the unique similar electronic system with the capability of quantum feedback in China so far.It has been already applied to China' s first on line quantum computer.The electronic feedback technology accumulated in quantum computing can also be applied to the field of quantum communication.Since the free-space interferom-eter is sensitive to environmental noise,how to ensure the phase stability of the op-tical information in the interferometer and maximize the interference visibility in the experiment is a problem that every experimenter needs to face.Aiming at the newly proposed quantum communication scheme in 2014,the round-robin differential phase shift quantum key distribution(RRDPS-QKD)protocal,this paper innovatively de?signs dynamic phase stabilization technique suitable for a set of 128 selectable delay path Mach-Zehnder interferometer used in the first time implementation of an original RRDPS-QKD.The innovations of this paper work are as follows:1.Originally developed a room temperature electronic readout system suitable for superconducting quantum computing.The real-time demodulation algorithm of qubit was realized in pipeline on the hardware,replacing the commercial high-speed acqui-sition cards used in the original experiment,which need off-line post processing by software.The readout system not only greatly improved the integration of supercon-ducting quantum computing experimental equipment,improving the number of qubit that can be read at one time during the experiment,but also shortened the experimen-tal time and increased the efficiency of the experiment.It took the lead in filling the blank in this field in China.By using this electronics system,we demonstrated the ex-periment of "genuine 12-Qubit entanglement on a superconducting quantum processor"and "strong correlated quantum walks with a 12-qubit superconducting processor" fisrt time in the world.2.For further dynamic quantum feedback circuit,the quantum state determination algorithm and low-latency ultra-high-speed serial communication protocol was origi-nally designed and realized.Cooperating with the self-developed arbitrary wave gen-erator,a closed loop of dynamic quantum feedback conditioned on the measurement of the qubit could be performed by the electronics readout system within 600 nanoseconds.And the important algorithm-active reset was successfully demonstrated.The readout system is the unique similar electronic system with the capability of quantum feedback in China so far.It has been already applied to China's first on-line quantum computer.3.Innovatively designed closed-loop feedback based phase stabilization technique suitable for a set of 128 selectable delay path Mach-Zehnder interferometer,ensuring the first time implementation of an original RRDPS-QKD protocol.