FIELD OF THE DISCLOSURE

The present disclosure relates to heat transfer devices, and more specifically to solid-state heat transfer devices.

BACKGROUND OF THE DISCLOSURE

Modern devices such as ultrafast quantum computers and sensors often require the use of extreme cold temperatures. Although techniques are available for achieving low temperatures, such as the use of dilution refrigerators, there continues to be an unmet need for a reliable heat transfer device that is able to achieve temperatures nearing absolute zero.

BRIEF SUMMARY OF THE DISCLOSURE

A solid state heat transfer technique is presented. The technique is based on repeated adiabatic magnetization/demagnetization cycles of a superconductor which acts as the working substance. The gradual cooling down of a substrate (normal metal) in contact with the working substance is demonstrated for different initial temperatures of the substrate. Excess heat is given to a hot large-gap superconductor. The on-chip refrigerator works in a cyclic manner because of an effective thermal switching mechanism: Heat transport between N/N versus N/S junctions is asymmetric because of the appearance of the energy gap. This switch permits selective cooling of the metal. We find that this refrigeration technique can cool down a 0.3 cm3block of Copper by almost two orders of magnitude starting from 200 mK, and down to about 1 mK starting from the base temperature of a dilution fridge (10 mK). The corresponding cooling power at 200 mK and 10 mK for a 1 cm×1 cm interface are 25 nW and 0.06 nW respectively, which scales with the area of the interface.

In an aspect, a heat transfer device is provided. The heat transfer device includes a working region made from a first superconducting material having a superconducting state and a normal state when magnetized. The first superconducting material has a first energy gap while in the superconducting state. The first superconducting material may be, for example, Tantalum, Aluminum, Tin, Mercury, or Indium. A metallic substrate is connected to the working region at a first tunnel junction. The metallic substrate may be made from, for example, Copper, Gold, Silver, or Aluminum doped with Manganese.

A heat sink is connected to the working region at a second tunnel junction. The heat sink is made from a second superconducting material. The second superconducting material has a second energy gap that is larger than the first energy gap. The second superconducting material may be, for example, Niobium, Niobium Nitride, Niobium-Titanium, Niobium Nitride-Titanium, Niobium-Germanium, Magnesium Diboride, or a covalent superconductor.

The first and/or second tunnel junctions may be insulators. The first and/or second tunnel junctions may be made from disordered oxides. For example, in an embodiment, the first and/or second tunnel junctions can be Tantalum Oxide (TaO and/or Ta2O5). In a particular example, the metallic substrate is Copper, the first superconducting material is Tantalum, and the second superconducting material is Niobium.

In some embodiments, the heat transfer device includes a magnetizer configured to adiabatically magnetize the working region so as to drive the first superconducting material to the normal state. The magnetizer may be, for example, a current source configured to selectively apply a supercurrent to the heat sink to induce a magnetic field. Other embodiments of magnetizers can be used as may be apparent in light of the present disclosure.

In some embodiments, the metallic substrate is suspended to reduce phonon-mediated thermal transport between the substrate and the working region. In some embodiments, the working region is suspended to reduce phonon-mediated thermal transport between the working region and the heat sink.

In another aspect, the present disclosure may be embodied as a sensor that includes a heat transfer device as described herein (e.g., the heat transfer device is a component of a sensor). In an example, the present disclosure may be embodied as a single-photon detector having a heat transfer device according to any of the embodiments described herein (e.g., the heat transfer device is a component of a single-photon detector).

In another aspect, the present disclosure may be embodied as a method for cooling a substrate. The method includes: providing a substrate connected to a working region at a first tunnel junction, wherein the working region is made from a first superconducting material having a first energy gap; applying a magnetic field to the working region to drive the first superconducting material to a normal state such that a first working temperature of the working region is less than a temperature of the substrate; reducing the magnetic field to drive the first superconducting material to a superconducting state such that the temperature of the working region is increased to a second working temperature; and providing a heat sink connected to the working region at a second tunnel junction, wherein the heat sink is made from a second superconducting material having a second energy gap larger than the first energy gap, and wherein a temperature of the heat sink is less than the second working temperature of the working region. In some embodiments, applying magnetic field to the working region includes applying a supercurrent to the heat sink.

