In my previous blog in quantum computing series, I described the difference between Classical Bit and Qubit.
This blog post is about how quantum bits are created, retained and read.
Classical Bit Storage
In classical computing, bits are stored in Hard Disk, Memory registers.
Hard Disk saves binary data as region of magnetic fields, if in hard disk magnetic field is present then that region will be considered as ‘1’ and if not then it is considered as ‘0’.
Memory Registers saves binary data in the form of electric charges for example, if it is charged then ‘1’ else ‘0’. The data itself is ON or OFF of +5-volt charge in the circuit.
And nowadays, there are various other storage devices which store the bits using their own way of storing, for example Solid State Drives, Compact Disks, etc.
But for storing and maintaining Qubit is a very tedious and complex process.
SuperConducting Quantum Bit Generation
There are natural Qubits like spin of an electrons or nucleus or phase change of photons.
To get better control and manipulation of Qubits, ‘Non Linear LC Resonator’ oscillator circuit is used to generate Man-made Qubit. Here ‘L’ stands for Inductor and ‘C’ stands for Capacitor. This circuit is called Non-Linear because Linear means continuously increasing or improvement in energy levels and Non-Linear means discrete like step by step increasing, when we apply electromagnetic waves to circuit, it will increase energy levels of electrons, and electron will move to next energy level having equally spaced energy levels as shown below, due to this equally space energy levels we cannot use the nature of quantum particles accurately.
A Josephson Junction is ciruit element used to restrict the quantum dynamic levels to two levels as shown below,
Using Josephson Junction, we can space these energy levels to unequally spaced energy levels or increase the space of energy level, after two energy levels we spaced another energy levels far away from the two, and now using those two energy levels
we can have superposition states and using those two energy levels we can depict various transition states. So using these circuit with Josephson junction is used to create and retain man made Qubit, and this is for a single Qubit generation, and for latest quantum computers we have multiple Qubits generation circuit. Below image is actual quantum processor, there you can see leads coming out of the quantum processor, these leads one can read the quantum state.
LC circuit is cooled down to very minimum temperature so that superconducting property of matter can be used and electrons will be in very minimum excitation state, using LC circuit with Josephson junction having two energy levels (one consider as 0 energy level and other can be consider as 1) we can reduce or restrict the electron to move to next energy state, so this how Josephson junction which is also called as Superconducting Quantum Interference Device (SQUID) works.
Squid is a magnetometer used to measure extremely low magnetic fields. This is the readout mechanism used to read the states of Qubits by read out lines as describe earlier the leads in processor. Leads also used to control the quantum state using the energy which we supply in the circuit.
Quantum Bit Generation
In classical processor, the connections are mostly done from the side of the chip. In some cases, from the downside.
In quantum processors, the leads are from the top. To preserve superconductivity, they are cooled by multi stage coolers based on pumping of cryogenic liquids. You can refer to this blog for how qubit is generated.
Quantum Decoherence
Maintaining quantum particles is a very tedious process, there is always a chance for the electron to absorb the energy from the surrounding and nearby particles then the property of quantum mechanics will be lost.
Decoherence is the process by which quantum particles interact with surroundings and returns back to its classical nature.
Coherence Time: How long a particle stay in quantum state ?
Due to this Quantum Decoherence nature of quantum particles, researchers are adding more and more circuits in the quantum processors, in order to maintain or retain Qubits.
This is how quantum bit is created, retained and read out using LC circuit with Josephson Junction.
In my next blog in Quantum computing series, I will write on Vector and Matrix Quantum States.
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Thank you for reading.