Diagnostic apparatus

1 . A diagnostic apparatus comprising:

a first array of superconducting quantum interference devices (SQUIDs), wherein each SQUID of the first array is configured to be coupled respectively to a test circuit of a second array of test circuits such that an electronic noise present in the test circuit induces a first current that flows through each SQUID of the first array; and

a current source configured to provide a second current for each SQUID of the first array such that the second current flows through each SQUID of the first array, wherein each SQUID of the first array is configured to generate an output in a form of:

a first voltage in response to a sum of the first current and the second current being less than a threshold current, and

a second voltage in response to the sum of the first current and the second current being greater than the threshold current, and

wherein a magnitude of the second current that flows through each SQUID is increased at a controlled rate with respect to time while generating the first current to cause the output to transition from the first voltage to the second voltage.

2 . The diagnostic apparatus of claim 1 , wherein the test circuit is configured to operate in an environment cooled by liquid nitrogen.

3 . The diagnostic apparatus of claim 1 , wherein the test circuit is configured to operate in an environment cooled by liquid helium.

4 . The diagnostic apparatus of claim 1 , wherein each SQUID of the first array is configured to be inductively coupled to the test circuit.

5 . The diagnostic apparatus of claim 1 , wherein each SQUID of the first array comprises a first terminal and a second terminal and each SQUID of the second array is configured to generate an output between the first terminal and the second terminal.

6 . The diagnostic apparatus of claim 1 , wherein the first voltage is substantially equal to zero.

7 . The diagnostic apparatus of claim 1 , wherein the first voltage is less than the second voltage.

8 . The diagnostic apparatus of claim 1 , wherein the test circuit comprises a complementary metal-oxide semiconductor (CMOS) circuit.

9 . A diagnostic system comprising:

a first array of test circuits;

a second array of superconducting quantum interference devices (SQUIDs), wherein each SQUID of the second array is coupled to a test circuit of the first array such that an electronic noise present in the test circuit induces a first current that flows through each SQUID of the second array; and

a current source configured to provide a second current for each SQUID of the second array such that the second current flows through each SQUID of the second array, wherein each SQUID of the second array is configured to generate an output in a form of:

a first voltage in response to a sum of the first current and the second current being less than a threshold current,

wherein a magnitude of the second current that flows through the SQUID is increased at a linear rate while generating the first current, and

a second voltage in response to the sum of the first current and the second current being greater than the threshold current.

10 . A method of operating a diagnostic apparatus, the method comprising:

generating, by the diagnostic apparatus and for each superconducting quantum interference device (SQUID) of a first array of SQUIDs and a corresponding test circuit of a second array of test circuits, a first current within the SQUID in response to detecting an electronic noise within the corresponding test circuit;

increasing, by the diagnostic apparatus and for each SQUID of the first array, a magnitude of a second current that flows through the SQUID while generating the first current; and

determining, by the diagnostic apparatus and for each SQUID of the first array, the magnitude of the second current at which an output of the SQUID transitions from a first voltage to a second voltage,

wherein determining the magnitude of the second current comprises:

using a magnitude of the first current and a time elapsed between a time of the first current to the transition to infer the magnitude of the second current when the SQUID transitions from the first voltage to the second voltage,

wherein the first voltage is output in response to a sum of the first current and the second current being less than a threshold current, and

wherein the second voltage is output in response to the sum of the first current and the second current being greater than the threshold current.

11 . The method of claim 10 , further comprising:

moving the diagnostic apparatus after performing the generating, the increasing, and the determining, and thereafter:

generating, for each SQUID of the first array and a corresponding test circuit of a third array of test circuits, a third current within the SQUID in response to detecting an electronic noise within the corresponding test circuit of the third array;

increasing, for each SQUID of the first array, a magnitude of a fourth current that flows through the SQUID while generating the third current; and

determining, for each SQUID of the first array, the magnitude of the fourth current at which an output of the SQUID transitions from the first voltage to the second voltage.

12 . The method of claim 10 , wherein the method comprises performing the generating, the increasing, and the determining, at least two times.

13 . The method of claim 12 , further comprising identifying, for each test circuit of the second array, the magnitude of the second current that corresponds to a Gaussian distribution.

14 . The method of claim 13 , further comprising identifying, for each test circuit of the second array, the magnitude of the second current that does not correspond to the Gaussian distribution.

15 . The method of claim 10 , wherein increasing the magnitude of the second current comprises increasing the magnitude at a first rate, the method further comprising performing the generating, the increasing, and the determining steps a second time, wherein the second time performing the increasing, comprises increasing the magnitude at a second rate that is greater than the first rate.

16 . The method of claim 10 , wherein the method is performed while the corresponding test circuit of the second array is operating in an environment cooled by liquid nitrogen.

17 . The method of claim 10 , wherein the method is performed while the corresponding test circuit of the second array is operating in an environment cooled by liquid helium.

18 . The method of claim 10 , wherein generating the first current comprises generating the first current via inductive coupling between the SQUID and the corresponding test circuit of the second array.

19 . The method of claim 10 , wherein the first voltage is substantially equal to zero.

20 . The method of claim 10 , wherein the first voltage is less than the second voltage.