Quantum state tomography plays a fundamental role in characterizing and evaluating the quality of quantum states produced by quantum devices. It serves as a crucial element in the advancement of quantum hardware and software, regardless of the underlying physical implementation and potential applications1,2,3. However, reconstructing the full quantum state becomes prohibitively expensive for large-scale quantum systems that exhibit potential quantum advantages4,5, as the number of measurements required increases exponentially with system size.
Recent protocols try to solve this challenge through two main steps: efficient parameterization of quantum states and utilization of carefully designed measurement schemes and classical data postprocessing algorithms. For one-dimensional (1D) systems with area law entanglement, the matrix product state (MPS)6,7,8,9,10,11,12 provides a compressed representation. It requires only a polynomial number of parameters that can be determined from local or global measurement results. Two iterative algorithms using local measurements, singular value thresholding (SVT)13 and maximum likelihood (ML)14, have been demonstrated in trapped-ion quantum simulators with up to 14 qubits15. However, SVT is limited to pure states and thus impractical for noisy intermediate-scale quantum (NISQ) systems. Meanwhile, although ML can handle mixed states represented as matrix product operators (MPOs)16,17, it suffers from inefficient classical data postprocessing.
The authors explore the digital-analog quantum computing paradigm, which combines fast single-qubit gates with the natural dynamics of quantum devices. They find the digital-analog paradigm more robust against certain experimental imperfections than the standard fully-digital one and successfully apply error mitigation techniques to this approach.
China’s efforts to scale up the manufacture of superconducting quantum computers have gathered momentum with the launch of the country’s independently developed third-generation Origin Wukong, said industry experts on Monday.
The latest quantum computer, which is powered by Wukong, a 72-qubit indigenous superconducting quantum chip, has become the most advanced programmable and deliverable superconducting quantum computer currently available in China.
The chip was developed by Origin Quantum, a Hefei, Anhui province-based quantum chip startup. The company has already delivered its first and second generations of superconducting quantum computers to the Chinese market.
Researchers from Tohoku University and the Massachusetts Institute of Technology (MIT) have unveiled a new AI tool for high-quality optical spectra with the same accuracy as quantum simulations, but working a million times faster, potentially accelerating the development of photovoltaic and quantum materials.
Scientists are finding ways to use quantum effects to create groundbreaking thermal devices that can help cool electronic systems. The quantum thermal transistor is one of the most exciting innovations in this field. While the current works surrounding this device are still theoretical, recent advancements in the fabrication of qubits using quantum dots and superconducting circuits have created a growing sense of optimism.
