Experimental Implementation of Noncyclic and Nonadiabatic Geometric Quantum Gates in a Superconducting Circuit

  1. Zhuang Ma,
  2. Jianwen Xu,
  3. Tao Chen,
  4. Yu Zhang,
  5. Wen Zheng,
  6. Dong Lan,
  7. Zheng-Yuan Xue,
  8. Xinsheng Tan,
  9. and Yang Yu
Quantum gates based on geometric phases possess intrinsic noise-resilience features and therefore attract much attention. However, the implementations of previous geometric quantum
computation typically require a long pulse time of gates. As a result, their experimental control inevitably suffers from the cumulative disturbances of systematic errors due to excessive time consumption. Here, we experimentally implement a set of noncyclic and nonadiabatic geometric quantum gates in a superconducting circuit, which greatly shortens the gate time. And also, we experimentally verify that our universal single-qubit geometric gates are more robust to both the Rabi frequency error and qubit frequency shift-induced error, compared to the conventional dynamical gates, by using the randomized benchmarking method. Moreover, this scheme can be utilized to construct two-qubit geometric operations, while the generation of the maximally entangled Bell states is demonstrated. Therefore, our results provide a promising routine to achieve fast, high-fidelity, and error-resilient quantum gates in superconducting quantum circuits.

Cancelling microwave crosstalk with fixed-frequency qubits

  1. Wuerkaixi Nuerbolati,
  2. Zhikun Han,
  3. Ji Chu,
  4. Yuxuan Zhou,
  5. Xinsheng Tan,
  6. Yang Yu,
  7. Song Liu,
  8. and Fei Yan
Scalable quantum information processing requires that modular gate operations can be executed in parallel. The presence of crosstalk decreases the individual addressability, causing
erroneous results during simultaneous operations. For superconducting qubits which operate in the microwave regime, electromagnetic isolation is often limited due to design constraints, leading to signal crosstalk that can deteriorate the quality of simultaneous gate operations. Here, we propose and demonstrate a method based on AC Stark effect for calibrating the microwave signal crosstalk. The method is suitable for processors based on fixed-frequency qubits which are known for high coherence and simple control. The optimal compensation parameters can be reliably identified from a well-defined interference pattern. We implement the method on an array of 7 superconducting qubits, and show its effectiveness in removing the majority of crosstalk errors.

Accelerated quantum adiabatic transfer in superconducting qubits

  1. Wen Zheng,
  2. Jianwen Xu,
  3. Zhimin Wang,
  4. Yuqian Dong,
  5. Dong Lan,
  6. Xinsheng Tan,
  7. and Yang Yu
Quantum adiabatic transfer is widely used in quantum computation and quantum simulation. However, the transfer speed is limited by the quantum adiabatic approximation condition, which
hinders its application in quantum systems with a short decoherence time. Here we demonstrate quantum adiabatic state transfers that jump along geodesics in one-qubit and two-qubit superconducting transmons. This approach possesses the advantages of speed, robustness, and high fidelity compared with the usual adiabatic process. Our protocol provides feasible strategies for improving state manipulation and gate operation in superconducting quantum circuits.

Suppression of static ZZ interaction in an all-transmon quantum processor

  1. Peng Zhao,
  2. Dong Lan,
  3. Peng Xu,
  4. Guangming Xue,
  5. Mace Blank,
  6. Xinsheng Tan,
  7. Haifeng Yu,
  8. and Yang Yu
The superconducting transmon qubit is currently a leading qubit modality for quantum computing, but gate performance in quantum processor with transmons is often insufficient to support
running complex algorithms for practical applications. It is thus highly desirable to further improve gate performance. Due to the weak anharmonicity of transmon, a static ZZ interaction between coupled transmons commonly exists, undermining the gate performance, and in long term, it can become performance limiting. Here we theoretically explore a previously unexplored parameter region in an all-transmon system to address this issue. We show that an experimentally feasible parameter region, where the ZZ interaction is heavily suppressed while leaving XY interaction with an adequate strength to implement two-qubit gates, can be found in an all-transmon system. Thus, two-qubit gates, such as cross-resonance gate or iSWAP gate, can be realized without the detrimental effect from static ZZ interaction. To illustrate this, we show that an iSWAP gate with fast gate speed and dramatically lower conditional phase error can be achieved. Scaling up to large-scale transmon quantum processor, especially the cases with fixed coupling, addressing error, idling error, and crosstalk that arises from static ZZ interaction could also be heavily suppressed.

Experimental Observation of Tensor Monopoles with a Superconducting Qudit

  1. Xinsheng Tan,
  2. Dan-Wei Zhang,
  3. Danyu Li,
  4. Xiaopei Yang,
  5. Shuqing Song,
  6. Zhikun Han,
  7. Yuqian Dong,
  8. Dong Lan,
  9. Hui Yan,
  10. Shi-Liang Zhu,
  11. and Yang Yu
Monopoles play a center role in gauge theories and topological matter. Examples of monopoles include the Dirac monopole in 3D and Yang monopole in 5D, which have been extensively studied
and observed in condensed matter or artificial systems. However, tensor monopoles in 4D are less studied, and their observation has not been reported. Here we experimentally construct a tunable spin-1 Hamiltonian to generate a tensor monopole and then measure its unique features with superconducting quantum circuits. The energy structure of a 4D Weyl-like Hamiltonian with three-fold degenerate points acting as tensor monopoles is imaged. Through quantum-metric measurements, we report the first experiment that measures the Dixmier-Douady invariant, the topological charge of the tensor monopole. Moreover, we observe topological phase transitions characterized by the topological Dixmier-Douady invariant, rather than the Chern numbers as used for conventional monopoles in odd-dimensional spaces.

High-fidelity, high-scalability two-qubit gate scheme for superconducting qubits

  1. Yuan Xu,
  2. Ji Chu,
  3. Jiahao Yuan,
  4. Jiawei Qiu,
  5. Yuxuan Zhou,
  6. Libo Zhang,
  7. Xinsheng Tan,
  8. Yang Yu,
  9. Song Liu,
  10. Jian Li,
  11. Fei Yan,
  12. and Dapeng Yu
High-quality two-qubit gate operations are crucial for scalable quantum information processing. Often, the gate fidelity is compromised when the system becomes more integrated. Therefore,
a low-error-rate, easy-to-scale two-qubit gate scheme is highly desirable. Here, we experimentally demonstrate a new two-qubit gate scheme that exploits fixed-frequency qubits and a tunable coupler in a superconducting quantum circuit. The scheme requires less control lines, reduces crosstalk effect, simplifies calibration procedures, yet produces a controlled-Z gate in 30ns with a high fidelity of 99.5%. Error analysis shows that gate errors are mostly coherence-limited. Our demonstration paves the way for large-scale implementation of high-fidelity quantum operations.

Experimental Realization of Universal Time-optimal non-Abelian Geometric Gates

  1. Zhikun Han,
  2. Yuqian Dong,
  3. Baojie Liu,
  4. Xiaopei Yang,
  5. Shuqing Song,
  6. Luqing Qiu,
  7. Danyu Li,
  8. Ji Chu,
  9. Wen Zheng,
  10. Jianwen Xu,
  11. Tianqi Huang,
  12. Zhimin Wang,
  13. Xiangmin Yu,
  14. Xinsheng Tan,
  15. Dong Lan,
  16. Man-Hong Yung,
  17. and Yang Yu
Based on the geometrical nature of quantum phases, non-adiabatic holonomic quantum control (NHQC) has become a standard technique for enhancing robustness in constructing quantum gates.
However, the conventional approach of NHQC is sensitive to control instability, as it requires the driving pulses to cover a fixed pulse area. Furthermore, even for small-angle rotations, all operations need to be completed with the same duration of time. Here we experimentally demonstrate a time-optimal and unconventional approach of NHQC (called TOUNHQC), which can optimize the operation time of any holonomic gate. Compared with the conventional approach, TOUNHQC provides an extra layer of robustness to decoherence and control errors. The experiment involves a scalable architecture of superconducting circuit, where we achieved a fidelity of 99.51% for a single qubit gate using interleaved randomized benchmarking. Moreover, a two-qubit holonomic control-phase gate has been implemented where the gate error can be reduced by as much as 18% compared with NHQC.

High-contrast ZZ interaction using multi-type superconducting qubits

  1. Peng Zhao,
  2. Peng Xu,
  3. Dong Lan,
  4. Xinsheng Tan,
  5. Haifeng Yu,
  6. and Yang Yu
For building a scalable quantum processor with superconducting qubits, the ZZ interaction is of great concert because of relevant for implementing two-qubit gates, and the close contact
between gate infidelity and its residual. Two-qubit gates with fidelity beyond fault-tolerant thresholds have been demonstrated using the ZZ interaction. However, as the performance of quantum processor improves, the residual static-ZZ can also become a performance-limiting factor for quantum gate operations and quantum error correction. Here, we introduce a scalable superconducting architecture for addressing this challenge. We demonstrate that by coupling two superconducting qubits with opposite-sign anharmonicities together, high-contrast ZZ interaction can be realized in this architecture. Thus, we can control ZZ interaction with high on/off ratio for implementing two-qubit CZ gate, or suppress it during the two-qubit gate operations using XY interaction (e.g. iSWAP). Meanwhile, the ZZ crosstalk related to neighboring spectator qubits can also be heavily suppressed in fixed coupled multi-qubit systems. This architecture could provide a promising way towards scalable superconducting quantum processor with high gate fidelity and low qubit crosstalk.

Realization of Superadiabatic Two-qubit Gates Using Parametric Modulation in Superconducting Circuits

  1. Ji Chu,
  2. Danyu Li,
  3. Xiaopei Yang,
  4. Shuqing Song,
  5. Zhikun Han,
  6. Zhen Yang,
  7. Yuqian Dong,
  8. Wen Zheng,
  9. Zhimin Wang,
  10. Xiangmin Yu,
  11. Dong Lan,
  12. Xinsheng Tan,
  13. and Yang Yu
We propose a protocol to realize parametric control of two-qubit coupling, where the amplitude and phase are tuned by a longitudinal field. Based on the tunable Hamiltonian, we demonstrate
the superadiabatic two-qubit quantum gate using superconducting quantum circuits. Our experimental results show that the state of qubits evolves adiabatically during the gate operation even though the processing time is close to the quantum limit. In addition, the quantum state transition is insensitive to the variation of control parameters, and the fidelity of a SWAP gate achieved 98.5%. This robust parametric two-qubit gate can alleviate the tension of frequency crowding for quantum computation with multiple qubits.

Experimental Measurement of the Quantum Metric Tensor and Related Topological Phase Transition with a Superconducting Qubit

  1. Xinsheng Tan,
  2. Dan-Wei Zhang,
  3. Zhen Yang,
  4. Ji Chu,
  5. Yan-Qing Zhu,
  6. Danyu Li,
  7. Xiaopei Yang,
  8. Shuqing Song,
  9. Zhikun Han,
  10. Zhiyuan Li,
  11. Yuqian Dong,
  12. Hai-Feng Yu,
  13. Hui Yan,
  14. Shi-Liang Zhu,
  15. and Yang Yu
Berry curvature is an imaginary component of the quantum geometric tensor (QGT) and is well studied in many branches of modern physics; however, the quantum metric as a real component
of the QGT is less explored. Here, by using tunable superconducting circuits, we experimentally demonstrate two methods to directly measure the quantum metric tensor for characterizing the geometry and topology of underlying quantum states in parameter space. The first method is to probe the transition probability after a sudden quench, and the second one is to detect the excitation rate under weak periodic driving. Furthermore, based on quantum-metric and Berry-curvature measurements, we explore a topological phase transition in a simulated time-reversal-symmetric system, which is characterized by the Euler characteristic number instead of the Chern number. The work opens up a unique approach to explore the topology of quantum states with the QGT.