Tiger in a Cage: Detecting Single Photons at low GHz Frequencies without Refrigerators, Vacuum Chambers or Magnets

被困在“笼”分子中的可光学极化的“自旋”分子将被合成并生长为分子晶体。一种这样的系统是吩嗪，作为自旋活性的“客体”分子，被作为“主体”分子的环蕃ExCage包封。据证实，这种分子工程系统可以提供N@C60所表现出的长自旋弛豫时间，同时更容易以高化学产率合成（和结晶出）。这一猜想将进行实验测试，通过瞬态EPR测量的弛豫时间被量化。进一步推测，这些系统能够通过客体分子的高空间浓度产生非常高的自旋极化密度，远远超过通过“稀释”系统如并五苯掺杂的对三联苯可以实现的自旋极化密度，其不能在不损害结晶度的情况下掺杂（在本体中）超过0.1%。作为“备份”，还将生长和评估自旋活性电荷转移晶体，例如吩嗪：四氰基苯（“TCNB”）。最有前途的分子系统，以适当形状的晶体的形式，然后将层压对压电芯片能够产生，传播和检测声延迟线结构中的表面声波（SAW）。芯片的衬底材料将是锂的选择的“切割”，SAW的产生和检测由光刻沉积在每个芯片表面上的相对的一对金属叉指换能器（IDT）提供。据推测，自旋极化晶体和SAW之间的耦合（当它在两个IDT之间传播时）将放大或衰减（=冷却）SAW，这取决于晶体是发射性还是吸收性自旋极化。免疫形式的电子噪声，限制了基于微波的放大器的性能，它进一步推测，与发射自旋极化晶体，该结构将作为雪崩光电倍增器，能够检测非常小的数量在室温下的微波光子。或者，使用吸收极化晶体，器件应该能够接近所讨论的自旋耦合SAW模式的量子基态（零光子）。器件将使用能够表示耦合的压电机械-微波SAW模式的先进有限元模拟软件进行精确模拟。将探索自旋极化晶体和SAW模式的各种组合[例如Rayleigh与Bleustein-Gulyaev]，以最大化自旋-声子耦合，同时避免SAW模式的过度“泄漏”（因此损耗）。脉冲和CW操作将被探讨。

Optically polarizable "spin" molecules trapped within "cage" molecules will be synthesized and grown as molecular crystals. One such system is phenazine, as the spin-active "guest" molecule, enveloped by a cyclophane ExCage as the "host" molecule. It is conjectured that such molecularly engineered systems can provide the long spin relaxation times exhibited by N@C60 whilst being far easier to synthesize (and crystallize out) at high chemical yields. This conjecture will be tested experimentally, the relaxation times being quantified through transient-EPR measurements. It is further speculated that these systems are capable of generating very high spin polarization densities by dint of the guest molecule's high spatial concentration, far exceeding what can be achieved by "dilute" systems such as pentacene-doped para-terphenyl, which cannot be doped (in the bulk) above 0.1 % without compromising crystallinity. As a "back-up", spin-active charge-transfer crystals, such as phenazine:tetracyanobenzene ("TCNB") will also be grown and assessed. The most promising molecular systems, in the form of suitably shaped crystals, will then be laminated against piezoelectric chips capable of generating, propagating and detecting surface-acoustic waves (SAWs) in acoustic delay line structures. The chips' substrate material will be a selected "cut" of lithium niobate, the generation and detection of SAWs being provided by an opposing pair of metal interdigital transducers (IDTs) lithographically deposited onto each chip's surface. It is speculated that the coupling between the spin-polarized crystal and the SAW (as it propagates between the two IDTs) will either amplify or attenuate (=cool) the SAW depending on whether the crystal is emissively or absorptively spin-polarised. Immune from the forms of electronic noise that limit the performance of semiconductor-based amplifiers, it is further speculated that, with an emissively spin-polarized crystal, the structure will function as an avalanche photo-multiplier capable of detecting very small numbers of microwave photons at room temperature. Alternatively, with an absorptively polarized crystal, the device should be capable of approaching the quantum ground state (zero photons) of the spin-coupled SAW mode in question.Devices will be accurately simulated using advanced finite-element simulation software capable of representing coupled piezomechanical-microwave SAW modes. Various combinations of spin-polarizable crystal and SAW mode [e.g. Rayleigh versus Bleustein-Gulyaev] will be explored towards maximizing the spin-phonon coupling whilst avoiding excessive "leakiness" (thus loss) from the SAW mode. Both pulsed and CW operation will be explored.