VLSI In Quantum Computing
blog written by:1. Asawari Sakharkar(B-39) 2. Tejas Rajuskar (B-30)3. Sanket Bandre (B-42)
Today is the world of High Speed we want to do things quickly … but our conventional computer and not satisfying this need, now this is a time to look into quantum computer which are known to have high speed 100000 than that of traditional computers in this blog we’ll see how is the basic chip, and memory bits requirements are satisfied
Quantum Computing (QC) is a computational paradigm where Quantum Mechanics (QM) is exploited for encoding information and doing calculations just like normal computers.
But then why are the different and how VLSI is helping to grown even more??
Let’s find out ………
Controlling a quantum computer is a lot like solving a Rubik’s Cube blindfolded and classic Rubik’s Cube has 43,252,003,274,489,856,000 different states. The initial state is well known, and there is a limited set of basic elements (qubits) that can be manipulated by a simple set of rules rotations of the vector that represents the quantum state. But observing the system during those manipulations comes with a severe penalty, if you take a look too soon, the computation will fail. That’s because you are allowed to view only the machine’s final state. Looks complicated right? But we are not going to talk in depth on the concept but rather .. on How VLSI helping to build more sophisticate quantum computers.
First let’s have a look on the first ever commercial quantum computer
But these system of 53 qubit has to be maintained at absolute 0K , so they are dipped in Liquid nitrogen for proper functioning because of heat the atoms vibrate and the qubits cannot be controlled, but other components cannot work at that temperature so they have to be maintained at least 3K.
Taking about the material used for making qubits they are made form superconducting metals
Now let’s go and see what remedy we have for lower temperature problem.
Here comes the role of VLSI, using CMOS technology INTEL in collaboration with QuTech have made an Quantum Chip which can sustain computations at 3 K which is only a little bit higher temperature than 0K but still it’s good because not the other electronics and the chip can be put in the same place .
This is called Horse Ridge, a cryogenic control chip that is capable of making quantum computers slimmer, faster, and less reliant on coolants.
Horse Ridge is fabricated using Intel’s 22nm FinFET Low Power (22FFL) technology.
Designed to act as a radio frequency (RF) processor to control the qubits operating in the refrigerator, Horse Ridge is programmed with instructions that correspond to basic qubit operations. It translates those instructions into electromagnetic microwave pulses that can manipulate the state of the qubits.
Named for one of the coldest regions in Oregon, the Horse Ridge control chip was designed to operate at cryogenic temperatures approximately 4 Kelvin. 4 Kelvin is only warmer than absolute zero a temperature so cold that atoms nearly stop moving.
Today, a quantum computer operates at in the millikelvin range just a fraction of a degree above absolute zero.
The chip is capable of handling a wide range of frequencies smaller spin qubits between 14GHz to 20GHz and superconducting qubits at 6GHz to 7GHz.
Now let’s discus more about these chips’, these are termed as Cryogenic Chips or Cyro chips because they are operated at lower temperatures (like 4K to 6K)
Now, MOS transistors are known to operate at 4K and below and thus CMOS could in principle be employed in a fault-tolerant loop. But how to fabricate these circuits on MOS ?
To understand the requirements of these circuits, let us consider the spin qubit
The above figure shows a SEM (Scanning Electron Micrograph) micrograph of the qubit; it is quantum dot (QD), where a single electron is confined, and a quantum point contact (QPC) to sense the spin of the electron by measuring the current flowing from SOURCE to DRAIN; a number of DC bias voltages are applied through contacts ‘M’, ’P’, ’R’, ’Q’, and ’T’, while the QPC is modelled as an RC circuit. The readout interface includes an I-to-V converter, a low-pass filter, and an A/D converter (ADC). An D/A converter may be used to generate the appropriate voltage V.
An extension of the concept to multi-qubit systems , where the circles at the lower level represent three quantum dots coupled through tunnelling barriers. Another dot (sensing quantum dot or SQD) senses the charges in the main dots by measurement of its conductance via direct DC current.
The vertical fat gates at the bottom are used to adjust the number of electrons in each dot, while the thin gates adjust the tunnel barrier couplings( dot = A Fat atom like Bismuth etc. these are injected into silicon crystal)
The implementation of CMOS multiplexers at base temperature (20mK, in this case) and the removal of SQD by means of dispersive readout techniques could accelerate the creation of large-scale classical-quantum interfaces.
This figure shows an generic system for a scalable qubit array where the majority of the components are operating at 4.5 K temperature, this circuitry performs local error correction, readout, and drives execution. Radio-frequency signals may be generated locally.
Compared to other fabrication techniques CMOS transistors are suitable for implementing multiplexing functions and more complex circuitry at even lower temperatures as well.
The FPGA, fabricated in a 28-nm CMOS process, performed well with performance comparable to that at room temperature. Differential and integral nonlinearity (DNL, INL) are plotted at 300K and 15K in figure below, achieving 8-bit resolution at 200MS/s.
References:-
1. https://www.vlsilab.polito.it/quantumcomputing/
3. https://en.wikipedia.org/wiki/Quantum_computing
5. Cryo-CMOS for Quantum Computing (E. Charbon1,2 F. Sebastiano1, A. Vladimirescu1,3,5, H. Homulle1, S. Visser1, L. Song1,4, R.M. Incandela11Delft University of Technology, Delft, The Netherlands, 2EPFL, Lausanne, Switzerland, 3Institut Supérieur d’Electronique de Paris, France, 4Tsinghua University, Beijing, China, 5UC Berkeley, Berkeley, USA.)
6. Electron heating and quasiparticle tunneling in superconducting charge qubits M. D. Shaw,1 J. Bueno,2 P. Delsing,2;3 and P. M. Echternach1;2
