Yo.Z. conceived the idea and supervised the experiment. S.L. supervised the device fabrication an... more Yo.Z. conceived the idea and supervised the experiment. S.L. supervised the device fabrication and supported the infrastructure setup. J.N. and Yo.Z. wirebonded the cables, performed the measurement and analyzed the data. L.Z. fabricated the devices and designed the sample holder. Y.L. and J.Q. assisted the measurement. Yo.Z. built the custom microwave electronics. Yo.Z. and A.N.C wrote the manuscript. All authors contributed to discussions and production of the manuscript.
Yo.Z. conceived the idea and supervised the experiment. S.L. supervised the device fabrication an... more Yo.Z. conceived the idea and supervised the experiment. S.L. supervised the device fabrication and supported the infrastructure setup. J.N. and Yo.Z. wirebonded the cables, performed the measurement and analyzed the data. L.Z. fabricated the devices and designed the sample holder. Y.L. and J.Q. assisted the measurement. Yo.Z. built the custom microwave electronics. Yo.Z. and A.N.C wrote the manuscript. All authors contributed to discussions and production of the manuscript.
Implementing quantum algorithms on realistic devices requires translating high-level global opera... more Implementing quantum algorithms on realistic devices requires translating high-level global operations into sequences of hardware-native logic gates, a process known as quantum compiling. Physical limitations, such as constraints in connectivity and gate alphabets, often result in unacceptable implementation costs. To enable successful near-term applications, it is crucial to optimize compilation by exploiting the capabilities of existing hardware. Here we implement a resource-efficient construction for a quantum version of AND logic that can reduce the compilation overhead, enabling the execution of key quantum circuits. On a high-scalability superconducting quantum processor, we demonstrate low-depth synthesis of high-fidelity generalized Toffoli gates with up to 8 qubits and Grover’s search algorithm in a search space of up to 64 entries. Our experimental demonstration illustrates a scalable and widely applicable approach to implementing quantum algorithms, bringing more meaningf...
Unwanted ZZ interaction is a quantum-mechanical crosstalk phenomenon which correlates qubit dynam... more Unwanted ZZ interaction is a quantum-mechanical crosstalk phenomenon which correlates qubit dynamics and is ubiquitous in superconducting qubit system. It adversely affects the quality of quantum operations and can be detrimental in scalable quantum information processing. Here we propose and experimentally demonstrate a practically extensible approach for complete cancellation of residual ZZ interaction between fixed-frequency transmon qubits, which are known for long coherence and simple control. We apply to the intermediate coupler that connects the qubits a weak microwave drive at a properly chosen frequency in order to noninvasively induce ac Stark shift for ZZ cancellation. We verify the cancellation performance by measuring vanishing twoqubit entangling phases and ZZ correlations. In addition, we implement randomized benchmarking experiment to extract the idling gate fidelity which shows good agreement with the coherence limit, demonstrating the effectiveness of ZZ cancellation. Our method allows independent addressability of each qubit-qubit connection, and is applicable to both non-tunable and tunable coupler, promising better compatibility with future large-scale quantum processors. Consider a general model described in Fig. 1(a), where two qubits Q 1 and Q 2 couple to an intermediate coupler C with a coupling strength of g 1c and g 2c , respectively, as well as to each other with a coupling strength g 12. The static Hamilto
Superconducting quantum circuits theory and application
Author(s): Deng, Xiuhao | Advisor(s): Chiao, Raymond | Abstract: Superconducting quantum circuit ... more Author(s): Deng, Xiuhao | Advisor(s): Chiao, Raymond | Abstract: Superconducting quantum circuit models are widely used to understand superconducting devices. This thesis consists of four studies wherein the superconducting quantum circuit is used to illustrate challenges related to quantum information encoding and processing, quantum simulation, quantum signal detection and amplification.The existence of scalar Aharanov-Bohm phase has been a controversial topic for decades. Scalar AB phase, defined as time integral of electric potential, gives rises to an extra phase factor in wavefunction. We proposed a superconducting quantum Faraday cage to detect temporal interference effect as a consequence of scalar AB phase. Using the superconducting quantum circuit model, the physical system is solved and resulting AB effect is predicted. Further discussion in this chapter shows that treating the experimental apparatus quantum mechanically, spatial scalar AB effect, proposed by Aharanov-Boh...
The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in manybody p... more The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in manybody physics, and it exhibits a Mott insulator (MI)-superfluid (SF) transition at integer filling. Here a quantum simulator of the BHM using a superconducting circuit is proposed. Specifically, a superconducting transmission line resonator supporting microwave photons is coupled to a charge qubit to form one site of the BHM, and adjacent sites are connected by a tunable coupler. To obtain a mapping from the superconducting circuit to the BHM, we focus on the dispersive regime where the excitations remain photon-like. Standard perturbation theory is implemented to locate the parameter range where the MI-SF transition may be simulated. This simulator allows singlesite manipulations and we illustrate this feature by considering two scenarios where a single-site manipulation can drive a MI-SF transition. The transition can be analyzed by mean-field analyses, and the exact diagonalization was implemented to provide accurate results. The variance of the photon density and the fidelity metric clearly show signatures of the transition. Experimental realizations and other possible applications of this simulator are also discussed.
Merced-The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in man... more Merced-The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in many body physics. Here a quantum simulator of the BHM using a superconducting circuit is proposed. Specifically, a superconducting transmission line resonator supporting microwave photons is coupled to a charge qubit to form one site of the BHM, and adjacent sites are connected by a tunable coupler. To obtain a mapping from the superconducting circuit to the BHM, we focus on the dispersive regime where the excitations remain photon-like. Standard perturbation theory is implemented to locate the parameter range where the BHM can be simulated. This simulator allows single-site manipulations and we illustrate this feature by considering two scenarios where a single-site manipulation can drive a Mott insulator-superfluid transition. The critical point of the transition can be located by mean-field analyses and the exact diagonalization method was implemented to provide accurate results. The variance of the density and the fidelity metric clearly show signatures of this transition. Experimental realizations and other possible applications of this simulator are also discussed.
We study a superconducting circuit that can act as a toolbox to generate various Bogoliubov-linea... more We study a superconducting circuit that can act as a toolbox to generate various Bogoliubov-linear and nonlinear quantum operations on the microwave photon modes of superconducting resonators within one single circuit. The quantum operations are generated by exploring dispersive four-wave mixing (FWM) processes involving the resonator modes. Different FWM geometries can be realized by adjusting the circuit parameters and by applying appropriate microwave drivings. We illustrate this scheme using a circuit made of two superconducting qubits that couple with each other. Each qubit couples with one superconducting resonator. We also discuss main sources of quantum errors in this system and study the fidelity of the quantum operations by numerical simulation. Our scheme provides a practical approach to realize quantum information protocols on superconducting resonators.
Via explicit examples we show that the pre-existing entanglement can really enhance ͑not only beh... more Via explicit examples we show that the pre-existing entanglement can really enhance ͑not only behave as an assistance for͒ the efficiency of the quantum error-correcting codes ͑QECCs͒ in a single block of encoding or decoding as well as help in beating the quantum Hamming bound. A systematic approach to constructing entanglement-assisted ͑or enhanced͒ quantum error-correcting codes ͑EAQECCs͒ via graph states is also presented, and an infinite family of entanglement-enhanced codes has been constructed. Furthermore we generalize the EAQECCs to the case of not-so-perfectly protected qubit and introduce the quantity infidelity as a figure of merit and show that the EAQECCs also outperform the ordinary QECCs.
We provide a systematic way of constructing entanglement-assisted quantum error-correcting codes ... more We provide a systematic way of constructing entanglement-assisted quantum error-correcting codes via graph states in the scenario of preexisting perfectly protected qubits. It turns out that the preexisting entanglement can help beat the quantum Hamming bound and can enhance (not only behave as an assistance) the performance of the quantum error correction. Furthermore we generalize the error models to the case of not-so-perfectly-protected qubits and introduce the quantity infidelity as a figure of merit and show that our code outperforms also the ordinary quantum error-correcting codes.
Yo.Z. conceived the idea and supervised the experiment. S.L. supervised the device fabrication an... more Yo.Z. conceived the idea and supervised the experiment. S.L. supervised the device fabrication and supported the infrastructure setup. J.N. and Yo.Z. wirebonded the cables, performed the measurement and analyzed the data. L.Z. fabricated the devices and designed the sample holder. Y.L. and J.Q. assisted the measurement. Yo.Z. built the custom microwave electronics. Yo.Z. and A.N.C wrote the manuscript. All authors contributed to discussions and production of the manuscript.
Yo.Z. conceived the idea and supervised the experiment. S.L. supervised the device fabrication an... more Yo.Z. conceived the idea and supervised the experiment. S.L. supervised the device fabrication and supported the infrastructure setup. J.N. and Yo.Z. wirebonded the cables, performed the measurement and analyzed the data. L.Z. fabricated the devices and designed the sample holder. Y.L. and J.Q. assisted the measurement. Yo.Z. built the custom microwave electronics. Yo.Z. and A.N.C wrote the manuscript. All authors contributed to discussions and production of the manuscript.
Implementing quantum algorithms on realistic devices requires translating high-level global opera... more Implementing quantum algorithms on realistic devices requires translating high-level global operations into sequences of hardware-native logic gates, a process known as quantum compiling. Physical limitations, such as constraints in connectivity and gate alphabets, often result in unacceptable implementation costs. To enable successful near-term applications, it is crucial to optimize compilation by exploiting the capabilities of existing hardware. Here we implement a resource-efficient construction for a quantum version of AND logic that can reduce the compilation overhead, enabling the execution of key quantum circuits. On a high-scalability superconducting quantum processor, we demonstrate low-depth synthesis of high-fidelity generalized Toffoli gates with up to 8 qubits and Grover’s search algorithm in a search space of up to 64 entries. Our experimental demonstration illustrates a scalable and widely applicable approach to implementing quantum algorithms, bringing more meaningf...
Unwanted ZZ interaction is a quantum-mechanical crosstalk phenomenon which correlates qubit dynam... more Unwanted ZZ interaction is a quantum-mechanical crosstalk phenomenon which correlates qubit dynamics and is ubiquitous in superconducting qubit system. It adversely affects the quality of quantum operations and can be detrimental in scalable quantum information processing. Here we propose and experimentally demonstrate a practically extensible approach for complete cancellation of residual ZZ interaction between fixed-frequency transmon qubits, which are known for long coherence and simple control. We apply to the intermediate coupler that connects the qubits a weak microwave drive at a properly chosen frequency in order to noninvasively induce ac Stark shift for ZZ cancellation. We verify the cancellation performance by measuring vanishing twoqubit entangling phases and ZZ correlations. In addition, we implement randomized benchmarking experiment to extract the idling gate fidelity which shows good agreement with the coherence limit, demonstrating the effectiveness of ZZ cancellation. Our method allows independent addressability of each qubit-qubit connection, and is applicable to both non-tunable and tunable coupler, promising better compatibility with future large-scale quantum processors. Consider a general model described in Fig. 1(a), where two qubits Q 1 and Q 2 couple to an intermediate coupler C with a coupling strength of g 1c and g 2c , respectively, as well as to each other with a coupling strength g 12. The static Hamilto
Superconducting quantum circuits theory and application
Author(s): Deng, Xiuhao | Advisor(s): Chiao, Raymond | Abstract: Superconducting quantum circuit ... more Author(s): Deng, Xiuhao | Advisor(s): Chiao, Raymond | Abstract: Superconducting quantum circuit models are widely used to understand superconducting devices. This thesis consists of four studies wherein the superconducting quantum circuit is used to illustrate challenges related to quantum information encoding and processing, quantum simulation, quantum signal detection and amplification.The existence of scalar Aharanov-Bohm phase has been a controversial topic for decades. Scalar AB phase, defined as time integral of electric potential, gives rises to an extra phase factor in wavefunction. We proposed a superconducting quantum Faraday cage to detect temporal interference effect as a consequence of scalar AB phase. Using the superconducting quantum circuit model, the physical system is solved and resulting AB effect is predicted. Further discussion in this chapter shows that treating the experimental apparatus quantum mechanically, spatial scalar AB effect, proposed by Aharanov-Boh...
The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in manybody p... more The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in manybody physics, and it exhibits a Mott insulator (MI)-superfluid (SF) transition at integer filling. Here a quantum simulator of the BHM using a superconducting circuit is proposed. Specifically, a superconducting transmission line resonator supporting microwave photons is coupled to a charge qubit to form one site of the BHM, and adjacent sites are connected by a tunable coupler. To obtain a mapping from the superconducting circuit to the BHM, we focus on the dispersive regime where the excitations remain photon-like. Standard perturbation theory is implemented to locate the parameter range where the MI-SF transition may be simulated. This simulator allows singlesite manipulations and we illustrate this feature by considering two scenarios where a single-site manipulation can drive a MI-SF transition. The transition can be analyzed by mean-field analyses, and the exact diagonalization was implemented to provide accurate results. The variance of the photon density and the fidelity metric clearly show signatures of the transition. Experimental realizations and other possible applications of this simulator are also discussed.
Merced-The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in man... more Merced-The Bose Hubbard model (BHM) of interacting bosons in a lattice has been a paradigm in many body physics. Here a quantum simulator of the BHM using a superconducting circuit is proposed. Specifically, a superconducting transmission line resonator supporting microwave photons is coupled to a charge qubit to form one site of the BHM, and adjacent sites are connected by a tunable coupler. To obtain a mapping from the superconducting circuit to the BHM, we focus on the dispersive regime where the excitations remain photon-like. Standard perturbation theory is implemented to locate the parameter range where the BHM can be simulated. This simulator allows single-site manipulations and we illustrate this feature by considering two scenarios where a single-site manipulation can drive a Mott insulator-superfluid transition. The critical point of the transition can be located by mean-field analyses and the exact diagonalization method was implemented to provide accurate results. The variance of the density and the fidelity metric clearly show signatures of this transition. Experimental realizations and other possible applications of this simulator are also discussed.
We study a superconducting circuit that can act as a toolbox to generate various Bogoliubov-linea... more We study a superconducting circuit that can act as a toolbox to generate various Bogoliubov-linear and nonlinear quantum operations on the microwave photon modes of superconducting resonators within one single circuit. The quantum operations are generated by exploring dispersive four-wave mixing (FWM) processes involving the resonator modes. Different FWM geometries can be realized by adjusting the circuit parameters and by applying appropriate microwave drivings. We illustrate this scheme using a circuit made of two superconducting qubits that couple with each other. Each qubit couples with one superconducting resonator. We also discuss main sources of quantum errors in this system and study the fidelity of the quantum operations by numerical simulation. Our scheme provides a practical approach to realize quantum information protocols on superconducting resonators.
Via explicit examples we show that the pre-existing entanglement can really enhance ͑not only beh... more Via explicit examples we show that the pre-existing entanglement can really enhance ͑not only behave as an assistance for͒ the efficiency of the quantum error-correcting codes ͑QECCs͒ in a single block of encoding or decoding as well as help in beating the quantum Hamming bound. A systematic approach to constructing entanglement-assisted ͑or enhanced͒ quantum error-correcting codes ͑EAQECCs͒ via graph states is also presented, and an infinite family of entanglement-enhanced codes has been constructed. Furthermore we generalize the EAQECCs to the case of not-so-perfectly protected qubit and introduce the quantity infidelity as a figure of merit and show that the EAQECCs also outperform the ordinary QECCs.
We provide a systematic way of constructing entanglement-assisted quantum error-correcting codes ... more We provide a systematic way of constructing entanglement-assisted quantum error-correcting codes via graph states in the scenario of preexisting perfectly protected qubits. It turns out that the preexisting entanglement can help beat the quantum Hamming bound and can enhance (not only behave as an assistance) the performance of the quantum error correction. Furthermore we generalize the error models to the case of not-so-perfectly-protected qubits and introduce the quantity infidelity as a figure of merit and show that our code outperforms also the ordinary quantum error-correcting codes.
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Papers by Xiuhao Deng