“Quantum Computers” – a word that was unheard to most of us even two decades ago has now stimulated the scientific community with a hope to provide breakthroughs in Science, Medicine and Machine Learning etc. From breaking encryption to revolutionizing artificial intelligence, quantum computers claim to outperform the traditional ones in terms of efficiency sometimes at an exponential scale. They are the strongest possible computational device offered to us by nature. Big shot companies like Google, IBM and Microsoft are spending billions and billions of dollars to create a reliable quantum computing facility. In October, 2019, Google claimed to have achieved “Quantum Supremacy” just by using an array of 54 qubits (out of which 53 were functional) to perform a series of operations which they claimed would have taken 10,000 years by the best supercomputer of the world!! Reportedly IBM objected to their claim saying it could take a few days only by a supercomputer. But who cares! Let the titans clash. Anyway, achieving quantum supremacy does not indicate that quantum computers are ready to perform right now. It’s a long way to go, but at least the road map is known to us.
Why Quantum Computers?
The computers that we use in our daily lives (like PCs, Laptops, Tablets, Smart-phones or even HPCs) are made up of chips, and those chips use bits as a fundamental unit to store and manipulate information. Bits are nothing but like tiny switches which can either be “ON” (representing a state) or “OFF” (another state), based on classical logic gate operations which manipulates the property “charge” of an electron and those operation rely on the very fundamental principle of classical physics that says at a given time, a physical system can stay in one and only one state. But universe doesn’t always work like that. Due to rapid progress in miniaturization, now chips are having typical dimensions around few square millimeters or even less and with millions of transistors in it. So, quantum effects are there and chip-makers tend to go to great lengths to suppress these effects. So, if we could rather manage ourselves to work with those effects then further miniaturization is possible providing a paradigm shift in computational performances. Not only is that, quantum computational algorithms are capable of handling ‘uncertainties’ and thus far better candidates to simulate biological and chemical complex systems.
How do they work?
In Quantum computers, qubits ( or ) are used instead of bits which are based on another property of electron named ‘spin’. According to Quantum mechanics, the state of a system can be a linear, coherent superposition of many different states, and thus capable to produce interference. Most magically, even two spatially separated states can be entangled to each other and therefore the operations on them have a non-local effect. Based on those properties qubits can be in many states (unlike “ON” and “OFF” for classical cases). For example, an n qubit system can be in 2n states while allowing entanglement between a n qubit state and m qubit states the number of possibilities enhances to 2m+n rather than 2n + 2m possibilities.
Analogous to the classical logic gate operations (like AND, OR and NOT), in quantum computation, the identity matrix and the Pauli matrices provide the 1 qubit logical operations. For example, the bitflip gate X turns to and vice-versa. The phaseflip gate Z puts a ‘-‘ sign in front of the qubit . Symbolically they are expressed as, and Similarly other operations are performed by sequential unitary operations.
Past, Present and Future…
This mind boggling concept was first coined by stalwarts like Yuri Mamin (1980), Richard Feynman (1981) and Paul Benioff. Later first designing of quantum Turing machine in 1985 by David Deutsch opened the gateway for unimaginable possibilities. Worldwide many groups are working now towards the success of quantum computation.
Till date two technologies are officially reported for creating qubits. One is by trapping ions and another is by using miniature superconducting circuits. IBM uses the later one. Problem is for doing anything with the qubits, coherence must be preserved as they are extremely sensitive to environmental noise.
In the attached figure (source: https://www.ibm.com/quantum-computing) you can see the dilution refrigerator made by IBM with nearly 2000 components for creating a super cold ambience so that the coherence of the qubits are being maintained.
Figure: Dilution refrigerator made by IBM for maintaining coherence for qubits
Till date the highest no of qubits are created by Google as reported in 2019 (an array of 54 qubits).
The future is unknown but we are hopeful for the unending offerings that quantum computers provide. It’s not like that we are going to have a quantum chip in our PC or smart-phone, and there will be no iphone Q, but for research and business purpose the possibilities are huge. From modeling of highly complicated chemical reactions, predicting early diagnosis of Alzheimer’s, to anticipating financial market, quantum algorithms claim to offer an unimaginable success. Cryptography can have an incredible makeover once quantum computation becomes successful. Rumors are there that various intelligence agencies over the world are stockpiling encrypted data with a hope that it can be decoded soon with the success of quantum computers. The only way to get saved from this is also within the realm of Quantum mechanics i.e., Quantum Encryption!! Think of a key that can’t be copied or hacked!! Quantum encrypted keys are exactly that.
It may sound a magical world, but it will happen in near future. Every breakthrough in science has passed through a dilemma and confusion. That’s the essence of Science. To unravel nature, to solve puzzle where the answer is embedded in it.
Such mysteries and possibilities make Physics as challenging and appealing as ever!!
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