Ultra high resolution Josephson sampling technique

Claim 2

A sampling system for measuring unknown signals, comprising: a superconducting monitor gate having at least two distinguishable states to which said unknown signal is applied as a control signal along with a sampling pulse and an adjustable bias signal, switching means for switching the state of said monitor gate, said switching means including a source of said unknown signal, a source of said sampling pulse, and a source of said adjustable bias signal, noise elimination means for unambiguously defining the switching threshold of said monitor gate, said noise elimination means including means for time averaging the voltage state of said monitor gate and being connected in a feedback loop between said source of bias signals and said monitor gate, said means for time averaging including means for applying an error signal to said source of bias signals in order to adjust the amplitude of said bias signal to that exact amplitude which switches the state of said monitor gate, a monitor gate current source for providing current through said monitor gate of a predetermined value, timing means for providing a timing reference and an accurate sampling delay time, said timing means including means for initiating the sampling of said unknown signal by said monitor gate and means for establishing a sampling delay time, said timing means including said source of sample pulses and a delay means for establishing a delay in the application of said sample pulses with respect to the application of said unknown signals, a trigger pulse source for providing trigger pulses to said source of unknown signals and to said source of sampling pulses to initiate the application of said unknown signal to said monitor gate and the application of said sampling pulse to said monitor gate, means for recording the state of said monitor gate at the instance of each said sampling pulse application, said recording means including means relating the magnitude of said bias signal to the magnitude of said unknown signal at each sampling instant.

Claim 3

The system of claim 1, further including a first adjustable delay line connected between said trigger pulse source and said source of sampling pulses, and a second delay line connected between said trigger pulse source and said source of unknown signals.

Claim 4

The system of claim 1, where said noise elimination means includes a phase sensitive amplifier and a comparator whose output is the error signal that is applied to the source of said bias signal.

Claim 5

The system of claim 1, where said monitor gate is comprised of a device exhibiting a Josephson current therethrough, said monitor gate being switchable between distinguishable voltage states by the presence of control signals comprising said unknown signal, said sampling pulse, and said bias signal.

Claim 6

The system of claim 4, where said monitor gate is comprised of an interferometer.

Claim 7

The system of claim 4, where said control signals are directly coupled to said device exhibiting a Josephson current therethrough.

Claim 8

The system of claim 4, where said source of unknown signals, said source of sampling pulses, and said monitor gate are located in a cryogenic environment.

Claim 9

The system of claim 4, where at least one of said unknown signals, said sample pulses, and said bias signals is applied as a control current in a conductor located adjacent to said monitor gate.

Claim 10

The system of claim 1, where said unknown signal is an optical beam directed onto a superconducting electrode of said monitor gate, said optical beam being of short duration which modifies the switching threshold of said monitor gate.

Claim 11

The system of claim 1, where said unknown signal is an electromagnetic signal and said bias signal is an electrical current.

Claim 12

The system of claim 1, where said monitor gate is comprised of a single junction exhibiting a Josephson tunnelling current.

Claim 13

A Josephson sampling system for measuring unknown signals, comprising: a superconducting monitor gate comprising a device exhibiting a Josephson tunnelling current, said monitor gate being switchable between two distinguishable states depending upon the incidence of control signals applied thereto and having at least first and second superconducting electrodes separated by a tunnel barrier, a gate current source for providing a gate current to one of the electrodes of said Josephson device, switch means for switching the state of said Josephson device including means for applying said unknown signal to said Josephson device, pulse means for applying sampling pulses to said Josephson device, and bias means for applying a bias current to said Josephson device, said sampling pulse and said bias current being directly coupled to one of the electrodes of said Josephson device while said gate current source is applied to the other electrode of said Josephson device, timing means for triggering the application of said unknown signal and said sampling pulse and for establishing a time interval between application of said sampling pulses, said timing means including a trigger pulse source for applying trigger pulses to said pulse means and to said means for applying said unknown signals, and further including delay means for delaying the application of said sample pulses with respect to said unknown signal in order to sample said unknown signal at preselected intervals of time, noise elimination means for eliminating the effects of noise and random events on the switching of said Josephson device in order to unambiguously define the switching threshold of said Josephson device in response to the combination of the control signals supplied by said unknown signal, said sampling pulses, and said bias current, said noise elimination means including means for developing an error signal representative of the deviation of the voltage read across one of the electrodes of said Josephson device with a reference voltage, and means for applying said error signal to said bias means to adjust the magnitude of said bias current to be that which, when combined with the magnitude of said sampling pulse and the magnitude of said unknown signal, will meet the threshold required for switching said Josephson device to one of its voltage states, said gate current through said Josephson device being held constant during any interval of time in which said sampling pulse is applied as a control input to said Josephson device, means including said trigger pulse source, said pulse means, and said delay means for providing repetitive sampling pulses to said Josephson device at the same instant of time relative to the unknown signal in order to time average said error signal over many cycles of sampling in order to eliminate effects on said Josephson device other than the switching effects produced by the simultaneous presence of said unknown signal, said sampling pulse, and said bias current.

Claim 14

A Josephson sampling system for measuring unknown signals, comprising: a superconducting monitor gate comprising a device exhibiting a Josephson tunnelling current, said monitor gate being switchable between two distinguishable states depending upon the incidence of control signals applied thereto and having at least first and second superconducting electrodes separated by a tunnel barrier, a gate current source for providing a gate current to one of the electrodes of said Josephson device, switch means for switching the state of said Josephson device including means for applying said unknown signal to said Josephson device, pulse means for applying sampling pulses to said Josephson device, and bias means for applying a bias current to said Josephson device, said sampling pulse and said bias current being directly coupled to one of the electrodes of said Josephson device while said gate current source is applied to the other electrode of said Josephson device, timing means for triggering the application of said unknown signal and said sampling pulse and for establishing a time interval between application of said sampling pulses, said timing means including a trigger pulse source for applying trigger pulses to said pulse means and to said means for applying said unknown signals, and further including delay means for delaying the application of said sample pulses with respect to said unknown signal in order to sample said unknown signal at preselected intervals of time, noise elimination means for eliminating the effects of noise and random events on the switching of said Josephson device in order to unambiguously define the switching threshold of said Josephson device in response to the combination of the control signals supplied by said unknown signal, said sampling pulses, and said bias current, said noise elimination means including means for developing an error signal representative of the deviation of the voltage read across one of the electrodes of said Josephson device with a reference voltage, and means for applying said error signal to said bias means to adjust the magnitude of said bias current to be that which, when combined with the magnitude of said sampling pulse and the magnitude of said unknown signal, will meet the threshold required for switching said Josephson device to one of its voltage states, said gate current through said Josephson device being held constant during any interval of time in which said sampling pulse is applied as a control input to said Josephson device, means including said trigger pulse source, said pulse means, and said delay means for providing repetitive sampling pulses to said Josephson device at the same instant of time relative to the unknown signal in order to time average said error signal over many cycles of sampling in order to eliminate effects on said Josephson device other than the switching effects produced by the simultaneous presence of said unknown signal, said sampling pulse, and said bias current.

Claim 15

The system of claim 12, where said Josephson device is comprised of a single tunnel junction including first and second superconducting electrodes and a tunnel barrier located therebetween.

Claim 16

The system of claim 12, wherein said noise elimination means includes a phase sensitive detector for comparing the voltage across one said Josephson device with a reference signal of the same phase, and a comparator means for developing an error signal representative of the difference between said voltage across said Josephson device and said reference voltage, and for applying said error signal to said bias means in order to vary said bias current.

Claim 17

The system of claim 12, including a recording means for representing said unknown signal in direct proportion to said bias current.

Claim 18

The system of claim 12, wherein said unknown signal is any electromagnetic signal of short duration which modifies the critical Josephson current by either an equilibrium mechanism or by the mechanism of pair breaking.

Claim 19

The system of claim 12, in which said unknown signal is an electromagnetic wave incident upon a superconducting electrode of said monitor gate.

Claim 20

The system of claim 12, where said unknown signal is a phonon beam of short duration, which modifies the Josephson switching threshold by the mechanism of pair breaking.

Claim 21

The system of claim 12, where said unknown signal is a particle beam of short duration, which modifies the Josephson switching threshold by the mechanism of pair breaking.

Claim 22

The system of claim 12, wherein said gate current through said Josephson device has a constant magnitude at any sampling time, and the algebraic sum of the amplitudes of said bias current, said sample pulse, and said unknown signal is equal to the amplitude of the switching threshold of said Josephson device for said constant amplitude of gate current therethrough.