分析人士预计“Q-Day”将在 2030 年代到来，届时量子计算机可在数天或数周内破解目前需经典超级计算机耗费数世纪才能解决的公钥加密（如 RSA）。其破坏力被比拟为从“盗走一个账户的钱”变成“偷光整个银行”，对机场、电网、通信网络与军事系统具备系统性瘫痪能力。美国智库估计，中国长期实施“先收集、后解密”策略，已囤积数十年通过网络攻击获取的数据，一旦获得具备纠错能力的量子机，可回溯破解敏感档案。量子威胁直接放大情报不对称风险，使北京可能在美、日、台完成量子抗性算法迁移之前获得情报与操控优势。

中国正投入 1 万亿元人民币（约 1,400 亿美元）国家基金布局半导体与量子技术，并已建成全球规模最大的量子通信基础设施，通过量子密钥分发实现“不可破解”链路。若美军或日本自卫队未在潜在冲突前完成量子抗性迁移，而中国率先取得具备密码学意义的量子机，则潜在后果包括劫持无人机与航母通信链路，使其偏航或失控。人口与军事领域的专家强调，美国各机构需遵循 2022 年发布的行政指令，在 2035 年前全面转向后量子算法，部分分析认为真正的量子威胁甚至可能更早出现。

然而专家指出，量子优势在战场上发挥作用仍需满足“战略奇袭”条件：国家必须隐藏突破并在适当时机集中使用。一旦国际社会察觉某方接近量子领先，将触发全球加速迁移，加密体系可在量子攻击生效前更新。因此当前关键在于提前完成量子抗性部署，以避免在 2030 年代面临一次性暴露所有军事、外交和情报通信内容的系统性风险。

Analysts project that “Q-Day” will arrive in the 2030s, when quantum computers will break today’s public-key encryption—such as RSA, which would take classical supercomputers centuries—in a matter of days or weeks. The destructive potential is described as shifting from “stealing one account” to “emptying the entire bank,” with capability to disrupt airports, power grids, telecom systems, and military platforms. US experts note China’s long-running “harvest now, decrypt later” strategy: decades of stolen data could be retrospectively decrypted once China obtains an error-corrected quantum machine, granting massive intelligence asymmetry before the US, Japan, or Taiwan complete migration to quantum-resistant algorithms.

China is committing a 1-trillion-yuan (about $140 billion) government-backed fund to “hard technologies” including quantum computing, and has built the world’s largest quantum communications network, relying on quantum key distribution for theoretically unbreakable links. If US or Japanese forces have not transitioned to quantum-resistant systems by a potential conflict while China fields a cryptographically relevant quantum computer, Beijing could hack drones, misdirect carriers, or penetrate battlefield communications. US policy requires all federal agencies to migrate to post-quantum algorithms by 2035, and some analysts believe a capable quantum system could emerge even sooner.

Experts caution that weaponizing quantum supremacy requires “strategic surprise”: the leading state would need to keep its capability secret and deploy it precisely once. Any indication that a nation is nearing quantum dominance would trigger global crash-program migrations to post-quantum cryptography. Thus, the decisive variable is not quantum hardware alone but whether nations execute the transition now, avoiding scenarios in which a single quantum breakthrough exposes all sensitive military, diplomatic, and intelligence communications.