SNF Issue No. 48, April 2020

In this Issue:

  • INTERNATIONAL SYMPOSIUM ON APPLIED SUPERCONDUCTIVITY (ISS 2019): Selected Plenary and Invited Presentations


Qubit Calibration by Remote Control

Figure 1aSeptember 9, 2020 (HP142).  Scientists at IBM have demonstrated a more general randomized benchmarking system by including an additional two-qubit primitive: the controlled-S phase (CS) gate. In their paper, “Experimental implementation of non-Clifford interleaved randomized benchmarking with a controlled-S gate,” [1] Shelly Garion of the IBM Research Haifa, Israel and Naoki Kanazawa of IBM Research Tokyo, Japan present a demonstration of a low-error non-Clifford CS gate. The CS is similar to a CZ in that it is a two-qubit gate that conditionally performs a phase rotation on a target qubit based on the state of a control qubit; however, the phase imparted is π/2 in the CS, whereas in the CZ it is π. Figure 1a shows the microwave pulse sequence used to perform the CS where the two-qubit interaction is accomplished via two cross-resonance (CR) pulses [2]. This non-Clifford two-qubit entangling gate is universal when combined with the Clifford group [3]. They incorporated the CS gate into their circuit construction and performed non-Clifford CNOT-Dihedral interleaved randomized benchmarking to measure the gate error at 5.9(7) × 10-3 for the CS with a gate time of 263 ns. Figure 1b shows that the CS gate error rates measured with both interleaved RB and quantum process tomography (QPT) approach the coherence limit.

This is an impressive result, made more so by the fact that it was accomplished by scientists who were not even on the same continent as the qubit itself. The experiment was performed through a remote Python interface on one of the quantum processors available through the IBM Quantum Experience platform. Customized control pulses were constructed using the open-source Qiskit Pulse framework by Kanazawa-san, and the calibration and refinement of the CS gate were accomplished without significant intervention during the experiment from lab personnel at IBM’s T.J. Watson Research Center in Yorktown Heights, NY, USA where IBM’s quantum computing systems are maintained.

Contributed by Tony Przybysz

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Measuring Fundamental Nuclear Data Using Metallic Magnetic Calorimeters: The European “Metrommc” Project

Metallic Magnetic Calorimeter image

June 17, 2020 (HP141). Metallic magnetic calorimeters (MMCs) are low-energy radiation detectors, operated usually below 100 mK, and consisting of an energy absorber in thermal contact with a metallic paramagnetic temperature sensor. The sensor is in a region where a weak magnetic field is applied, so that a temperature increase due to radiation absorption produces a change in the sensor magnetization detectable by a superconducting quantum interference device (SQUID) as a change of magnetic flux. These detectors have shown in recent years to possess the unique combination of high-resolution, low energy threshold, and high degree of linearity, all of which are needed for precise measurement of low-energy nuclear and atomic radiation. Several projects worldwide are currently ongoing to exploit MMCs in a variety of fields including nuclear, particle physics and astrophysics, medical, nuclear safeguard, and nuclear forensics.

Submitted by The MetroMMC collaboration

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