{"product_id":"squidra-dc-squid","title":"Squidra – The dc SQUID \/ Period Φ0 Physics Sticker","description":"\u003cp\u003eSquidra, a superconducting sorcerer, cradles a glowing ring of current that can feel a fraction of a single flux quantum.\u003c\/p\u003e\u003ch3\u003eThe Physics\u003c\/h3\u003e\u003cp\u003eA dc SQUID is a superconducting loop broken by two Josephson junctions. The current waves through the two junctions interfere, so the voltage across the device swings periodically as the magnetic flux through the loop changes. One full period is one flux quantum. R. C. Jaklevic, J. Lambe, A. H. Silver and J. E. Mercereau first showed this interference (“Quantum Interference Effects in Josephson Tunneling”, Phys. Rev. Lett. 12, 159, 1964).\u003c\/p\u003e\u003cp\u003e\u003cstrong\u003eΦ\u003csub\u003e0\u003c\/sub\u003e = h\/2e ≈ 2.067833848 × 10⁻¹⁵ Wb\u003c\/strong\u003e\u003c\/p\u003e\u003cul\u003e\n\u003cli\u003eΦ\u003csub\u003e0\u003c\/sub\u003e: magnetic flux quantum (weber, Wb)\u003c\/li\u003e\n\u003cli\u003eh: Planck constant\u003c\/li\u003e\n\u003cli\u003e2e: charge of a Cooper pair\u003c\/li\u003e\n\u003c\/ul\u003e\u003cp\u003eSince the 2019 SI redefinition, h and e have exact values, so Φ\u003csub\u003e0\u003c\/sub\u003e is exact too. Measuring a small fraction of a period makes SQUIDs the most sensitive magnetometers known, used to read signals from the brain.\u003c\/p\u003e\u003cp\u003e\u003cem\u003eHonest caveat:\u003c\/em\u003e The voltage is periodic in Φ\u003csub\u003e0\u003c\/sub\u003e, but its exact shape depends on the junctions and bias current. The 2e is there because the charge carriers are electron pairs.\u003c\/p\u003e\u003ch3\u003eOn the sticker\u003c\/h3\u003e\u003cp\u003eSquidra holds a glowing cyan ring between his hands; the two junctions are not clearly drawn. Printed text: \u003cstrong\u003eSQUIDRA\u003c\/strong\u003e with the line \u003cstrong\u003ePERIOD Φ0\u003c\/strong\u003e. Pixel-art kiss-cut vinyl sticker, white, in 2″, 3″, 4″ and 6″ sizes.\u003c\/p\u003e","brand":"Printify","offers":[{"title":"2\" × 2\" \/ White","offer_id":50964017905767,"sku":"24880154231273632013","price":4.99,"currency_code":"USD","in_stock":true},{"title":"3\" × 3\" \/ White","offer_id":50964017938535,"sku":"11444310917400718387","price":6.99,"currency_code":"USD","in_stock":true},{"title":"4\" × 4\" \/ White","offer_id":50964017971303,"sku":"24093340995766768127","price":8.99,"currency_code":"USD","in_stock":true},{"title":"6\" × 6\" \/ White","offer_id":50964018004071,"sku":"14145531526995776372","price":11.99,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0596\/8746\/9159\/files\/18427719818092941722_1200.jpg?v=1793658068","url":"https:\/\/pixelatedphysics.com\/zh-hans\/products\/squidra-dc-squid","provider":"Pixelated Physics","version":"1.0","type":"link"}