Description
Speaker:
Prof Kihwan Kim
Tsinghua University
Abstract:
Quantum coherence fundamentally limits quantum computer and memory performance. While trapped atomic ions theoretically support million-year coherence based on spontaneous emission, experimental demonstrations have fallen orders of magnitude short. This gap raises whether we face fundamental physical limitations or addressable technical challenges.
We combine clock-state qubits with decoherence-free subspace (DFS) encoding to achieve coherence times exceeding ten hours—an order-of-magnitude improvement. Using 171Yb+ ion pairs sympathetically cooled by 138Ba+, we demonstrate this without magnetic shielding or enhanced microwave stabilization. DFS encoding cancels common-mode magnetic fluctuations across micrometer separations while clock states provide environmental insensitivity.
Our exponential fits yield a coherence time of 37,750 ± 10,890 seconds. These results experimentally verify that trapped-ion qubits are limited by technical factors rather than fundamental decoherence, establishing a pathway toward ultimate quantum memories for scalable information processing. I will also discuss our related work on scaling up qubit numbers using two-dimensional ion crystals.