Electro-optic quantum coherent interfaces map the amplitude and phase of a quantum signal directly to the phase or intensity of a probe beam. At terahertz frequencies, a fundamental challenge is not only to sense such weak signals (due to a weak coupling with a probe in the near-infrared) but also to resolve them in the time domain. Cavity confinement of both light fields can increase the interaction and achieve strong coupling. Using this approach, current realizations are limited to low microwave frequencies. Alternatively, in bulk crystals, electro-optic sampling was shown to reach quantum-level sensitivity of terahertz waves. Yet, the coupling strength was extremely weak. Here, we propose an on-chip architecture that concomitantly provides subcycle temporal resolution and an extreme sensitivity to sense terahertz intracavity fields below 20 V/m. We use guided femtosecond pulses in the near-infrared and a confinement of the terahertz wave to a volume of ${V_{\rm THz}} \sim {10^{- 9}}{({\lambda _{\rm THz}}/2)^3}$ in combination with ultraperformant organic molecules (${r_{33}} = 170\,\,{\rm pm}/{\rm V}$) and accomplish a record-high single-photon electro-optic coupling rate of ${g_{\!{\rm eo}}} = 2\pi \times 0.043\,\,{\rm GHz}$, 10,000 times higher than in recent reports of sensing vacuum field fluctuations in bulk media. Via homodyne detection implemented directly on chip, the interaction results into an intensity modulation of the femtosecond pulses. The single-photon cooperativity is ${C_0} = 1.6 \times {10^{- 8}}$, and the multiphoton cooperativity is $C = 0.002$ at room temperature. We show ${\gt}{70}\;{\rm dB}$ dynamic range in intensity at 500 ms integration under irradiation with a weak coherent terahertz field. Similar devices could be employed in future measurements of quantum states in the terahertz at the standard quantum limit, or for entanglement of subsystems on subcycle temporal scales, such as terahertz and near-infrared quantum bits.

中文翻译：

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电光接口，用于在微波和太赫兹频率下进行超灵敏腔内电场测量

电光量子相干接口将量子信号的幅度和相位直接映射到探测光束的相位或强度。在太赫兹频率下，根本的挑战不仅是感测这种微弱的信号（由于与近红外探头的耦合较弱），而且还要在时域内解决它们。两个光场的腔约束可以增加相互作用并实现强耦合。使用这种方法，当前的实现仅限于低微波频率。另外，在块状晶体中，电光采样显示达到太赫兹波的量子级灵敏度。然而，耦合强度极弱。这里，我们提出了一种片上架构，可同时提供子周期时间分辨率和极高的灵敏度，以感测低于20 V / m的太赫兹腔内场。我们在近红外中使用引导的飞秒脉冲，并将太赫兹波限制在$ {V _ {\ rm THz}} \ sim {10 ^ {-9}} {（{\ lambda _ {\ rm THz}} / 2）^ 3} $与超高性能有机分子（$ {r_ {33 }} = 170 \，\，{\ rm pm} / {\ rm V} $），并达到创纪录的单光子电光耦合率$ {g _ {\！{\ rm eo}}} =比最近检测到大容量介质中真空场波动的报告高出10,000倍，是2 pi×0.043，\，{\ rm GHz} $。通过直接在芯片上实现的零差检测，相互作用导致飞秒脉冲的强度调制。在室温下，单光子协同度为$ {C_0} = 1.6 \乘以{10 ^ {-8}} $，而多光子协同度为$ C = 0.002 $。我们显示$ {\ gt} {70} \; {\ rm dB} $弱相干太赫兹场辐射下500 ms积分强度的动态范围。类似的设备可用于将来在标准量子极限下对太赫兹中的量子态进行测量，或用于子系统在子周期时间尺度上的纠缠，例如太赫兹和近红外量子位。