*: co-first author †: corresponding author

Recent works

Probing the Error-Mitigation Threshold with Matrix Product States

J. Zhao, ZYW†, M. J. Gullans†, arXiv:2609.10929

We study when quantum error mitigation (QEM) remains reliable despite imperfect knowledge of noise. By mapping the problem to a statistical-physics model and developing an MPS-based method for large-scale simulations, we uncover a sharp threshold: QEM remains stable when the noise-model mismatch is small, but breaks down when it becomes too large. Our approach makes it possible to reveal this “phase-transition” behavior in large 2D quantum architectures.

Fock-state preparation based on amplitude amplification in cavity QED

S. Austin, ZYW, K. Srinivasan, A. V. Gorshkov, arXiv:2607.14239

We bring Grover-style amplitude amplification to coherent control in cavity QED, enabling more efficient preparation of traveling single photons and nonclassical cavity states. Our protocols provide quadratic improvements in preparation length, can reduce intrinsic cavity-loss errors, and extend to Fock and NOON states.

Measurement-enhanced entanglement in a monitored superconducting chain

R. Guo, J. Chen†, ZYW†, arXiv:2604.04375 [Letter]

R. Guo, ZYW, arXiv:2607.07835 [Companion Article]

Monitored quantum dynamics has attracted broad interest for revealing fascinating phenomena such as measurement-induced phase transitions (MIPT). A common view in these settings is that local measurements suppress entanglement. We show that in a monitored s-wave superconducting chain, however, the opposite can occur: local measurements can enhance entanglement growth during the dynamics!

The key mechanism is the competition between superconducting pairing and measurement. Pairing suppresses entanglement growth, while measurements suppress pairing—so increasing the measurement rate can counterintuitively enhance entanglement growth. 

Using exact numerics and analytical nonlinear sigma-model (NLSM) calculations, we also show that at small but finite measurement rates, the steady-state entanglement exhibits an unusual super-logarithmic scaling, S(L)=O(log^2 L).

Weighted Nested Commutators for Scalable Counterdiabatic State Preparation

J. Tang, X. Chen†, ZYW†, arXiv:2603.25625

Counter-diabatic driving relies on the adiabatic gauge potential (AGP), but the exact AGP is usually hard to compute and implement. We introduce a new variational ansatz, the weighted nested-commutator (WNC) ansatz, which assigns independent parameters to local terms and greatly improves expressiveness over the standard NC approach. With an efficient local optimization method, WNC enables faster large-scale quantum state preparation, including 1D many-body systems with up to 1000 qubits and the 2D AKLT state on a hexagonal lattice, underscoring the promise of CD driving for scalable quantum state preparation.

Noise-induced contraction of MPO truncation errors in noisy random circuits and Lindbladian dynamics

ZYW†, J. Rajakumar, J. Nelson, D. Malz, M. J. Gullans, A. V. Gorshkov, arXiv:2603.20400

Matrix product operators (MPOs) are widely used to simulate mixed-state quantum systems, yet MPO-based algorithms have long lacked controllable upper bounds on the trace-norm (L_1) error, limiting their applicability. We study MPO simulation errors for noisy 1D random quantum circuits and Lindblad dynamics, and find that the simulation error contracts exponentially under noisy evolution. This leads to an empirical error bound that is exponentially tighter than existing bounds, which in turn suggests that MPO methods may efficiently (i) sample from the evolved states of one-dimensional random quantum circuits with non-unital noise, and (ii) sample from the steady states of one-dimensional Lindbladian dynamics.

Measurement-induced entanglement in noisy 2D random Clifford circuits

ZYW†, J. Nelson, J. Rajakumar, E. Cruz, A. V. Gorshkov, M. J. Gullans, D. Malz, PRX Quantum (2026)

We show that even tiny, constant noise can eliminate long-range, volume-law measurement-induced entanglement in 2D quantum Clifford circuits. This result implies that a tensor-network–based method (designed for generic circuits) can potentially efficiently sample from noisy 2D random Clifford circuits—in polynomial time—(i) throughout the entire sub-logarithmic-depth regime for any fixed noise rate, and (ii) at constant depths for noise rates scaling as p ≈ 1/ log N.

The results give new insight into how noise constrains quantum entanglement and the complexity of 2D noisy random circuits.

Kondo impurity in an attractive Fermi-Hubbard bath: Equilibrium and dynamics

ZYW*, T. Shi*†, J. I. Cirac, E. Demler. Kondo impurity in an attractive Fermi-Hubbard bath: Equilibrium and dynamics. arXiv:2501.05562

Fig. (a) Kondo impurity in an attractive Hubbard bath. (b) First-order phase transition between the singlet and the doublet ground states. (c) Charge transport dynamics under bias voltage V. (d) Transport dynamical `phase diagram' with rich behaviors.

Renormalization-group-based preparation of matrix product states on up to 80 qubits

M. Scheer, A. Baiardi, E. Baumer, ZYW, D. Malz, arXiv:2510.24681

We experimentally realized the RG algorithm [Malz*, Styliaris*, ZYW* (alphabetical order), Cirac. PRL (2024)] on a superconducting quantum processor — preparing symmetry-protected topologically (SPT) ordered states with up to 80 qubits (largest to date). This demonstrates how the RG algorithm enables large-scale preparation of entangled quantum states on near-term devices.

Earlier works

Preparation of tensor network states

1. ZYW*, D. Malz*, J.I. Cirac. Sequential generation of projected entangled-pair states. PRL (2022)

2. ZYW, D. Malz, J.I. Cirac. Efficient Adiabatic Preparation of Tensor Network States. PR Research (2023) (Letter)

3. D. Malz*, G. Styliaris*, ZYW* (alphabetical order), J.I. Cirac. Preparation of matrix product states with log-depth quantum circuits. PRL (2024)

4. ZYW†, D. Malz†. State preparation with parallel-sequential circuits. Quantum (2026)

Tensor network states (TNS), such as the matrix product states (MPS) and projected entangled pair states (PEPS), are paradigmatic states to describe the ground states of gapped Hamiltonians, and they include important states such as the cluster, W, GHZ, AKLT states. There is thus increasing interest in finding ways of preparing them in quantum computers or quantum simulators, either for quantum information applications like computing, metrology, communication, and networking, or as variational states for the study of many-body quantum systems. It is well-known that the MPS of the system size N can be prepared with circuit depth T=O(N). However, two pressing questions have not been fully resolved: Which subclass of high-dimensional PEPS can be efficiently prepared, and what is the optimal scaling for preparing different kinds of TNS?

Our works [1-4] are significant steps toward the efficient preparation of TNS. In [1,2], we develop schemes to efficiently prepare high-dimensional PEPS. In [1], we introduce Plaquette-PEPS, which is a subclass of PEPS that encodes important states such as the graph states and topologically ordered states. We provide an efficient scheme to prepare them with the circuit depth that scales with the linear dimension of the system, which is optimal for preparing states with topological order. In [2], we discover an adiabatic path that allows preparing short-range correlated TNS with evolution time T~ polylog N, which serves as the first deterministic method to create the high-dimensional AKLT states. In [3], we prove that one needs at least a logarithmically growing circuit depth to prepare short-range correlated MPS faithfully and develop an algorithm to prepare these MPS with such optimal scaling. By further utilizing measurements, we can prepare almost arbitrary MPS with circuit depth T=O(log log N), which is exponentially faster than known methods to prepare them. In [4], we introduce parallel-sequential (PS) circuits, a family of quantum circuit layouts that unify and generalize the brickwall and sequential circuits, which allows the efficient preparation of many-body ground states. 

Fig. (a) Sequential preparation of (long-range correlated) PEPS. (b) Adiabatic preparation of short-range correlated PEPS (such as AKLT states). (c) Preparation of MPS with log-depth circuits. (d) Parallel-sequential (PS) circuits. 

Physical platforms to create large-scale photonic entanglement

1. ZYW, D. Malz, A.G.-Tudela, J.I. Cirac. Generation of photonic matrix product states with Rydberg atomic arrays. PR Research (2021)

2. ZYW†, J.I. Cirac, D. Malz†. Generation of photonic tensor network states with circuit QED. PRA (2022)

A key element in photonic quantum information processing is to prepare large-scale photonic entanglement. We design an efficient light-matter interface using sub-wavelength Rydberg atomic arrays to prepare optical photonic MPS in free space [1] and use a circuit QED system to prepare microwave photonic MPS and PEPS [2]. Both of our schemes can prepare a large number of entangled photons, and relevant experiments have demonstrated the effectiveness of these schemes. 

Fig. Generation and distribution of multi-photon entanglement with (a) Rydberg atomic arrays and (b) microwave cavity QED system.

Measuring quantum coherence using the interference fringes

Y.T. Wang, J.S. Tang, ZYW, S. Yu, Z.J. Ke, X.Y. Xu, C.F. Li, G.C. Guo, "Directly measuring the degree of quantum coherence using interference fringes." PRL(2017)

We develop a method to measure quantum coherence directly using its most essential behavior—the interference fringes. The ancilla states are mixed into the target state with various ratios, and the minimal ratio that makes the interference fringes of the “mixed state” vanish is taken as the quantity of coherence. We also use the witness observable to witness coherence, and the optimal witness constitutes another direct method to measure coherence. For comparison, we perform tomography and calculate the L1 norm of coherence, which coincides with the results of the other two methods in our situation and shows the effectiveness of our method.

Fig. Experimental setup.