在深夜用英语可以说 "in the dead of night"。这个短语源自古英语，其中 "dead" 意为 "非常深" 或 "完全"，"night" 指 "夜晚"。例如：

She snuck out of the house in the dead of night.

The thieves broke into the museum in the dead of night.

He sat alone in his room, thinking, in the dead of night.