The Quantum Leap

Quantum Gap

During the presentation and class discussion with John Donovan of AT&T the topic of quantum computing and quantum networking was briefly addressed. It occurred to me that Jeff Welsler of IBM had also talked about quantum computing, and efforts to offer that capability to consumers via the cloud. As evidence by its prevalence in recent presentations quantum computing is an exciting and evolving technology with far reaching implications. Repeated allusions to the topic prompted me to ask the question, what is quantum computing and why should I care ? Unfortunately the answers are much more complicated than the question. On his site, Nielsen explains the “quantum gap” that complicates the answers [1].

In my professional life I often view problems in binary terms, ones and zeros. This is how modern computers see the world, but it introduces stark differences between modern computers and quantum computers. As Nielsen explains, when we look to understand and conceptualize things we search for concrete, conventional explanation of a kind that can be simulated with conventional computing. Unfortunately for us (but fortunately for the usefulness of quantum computing) “quantum computers cannot be explained in simple concrete terms; if they could be, quantum computers could be directly simulated on conventional computers, and quantum computing would offer no advantage over such computers”[1]. In other words, quantum computers simply don’t follow the rules we generally use to explain and understand the world around us. Because of this, I will restrict this post to highlighting some of the main differences between conventional and quantum computing and touch on the potential impact.

Bits vs Qubits

While conventional computers use bits, the quantum computer equivalent are things called quantum bits or “quibits”. While conventional bits are definitively either a one or a zero a qubit “can store much more information than just 1 or 0, because they can exist in any superposition of these values”[2]. In their article, Wired describes this difference and the implication succinctly “A qubit can be thought of like an imaginary sphere. Whereas a classical bit can be in two states – at either of the two poles of the sphere – a qubit can be any point on the sphere. This means a computer using these bits can store a huge amount more information using less energy than a classical computer.”[2] Current, state of the art quantum computers might contain anywhere from 5 to 10 qubits. While a conventional computer containing five bits is not of much use, because a qubit can exist in a 0 state, a 1 state, or any superposition state “between” the two simultaneously the power and information encoded in a qubit compared to a bit is vastly increased.  “A 30-qubit quantum computer would equal the processing power of a conventional computer that could run at 10 teraflops (trillions of floating-point operations per second). “[4]

Measurement and Entanglement

Another major difference and complication between conventional bits and qubits is that when measuring a qubit, the state is inherently altered. When observing the state of a conventional bit, we have the ability to read the value and we expect that value to persist unless expressly changed. With quantum computing this is no longer true. While a qubit can exist in superpositions between 0 and 1, when it is observed it will assume the value of either a 0 or a 1 but not both. In a way, this is good because it allows us to produce concrete and useful results from qubits (the answer to a question isn’t very useful if it is both yes and no at the same time …), but it raises the following interesting question. If observing the value of a qubit changes its value, how can we measure them to make any use of them?

The answer seemingly lies in another bizarre fundamental concept of quantum computing called entanglement. In a conventional computer we expect to observe the value of any given bit, and can safely assume that doing so does not somehow alter the states of other bits in the system. With quantum theory this is no longer true. If an outside force it applied, two atoms or qubits can become “entangled” meaning that the state of one is not independent of the other. From what we have observed, if the first atom chooses one spin or value, at the same time the other entangled atom chooses the opposite [4] allowing us to measure the value of a given qubit without measuring it directly.

Who Cares?

At the moment, this technology may seem so unconventional and mystical (the IBM implementation uses artificial atoms at .015 kelvin which is colder than outer space)[5] that its use cases would be of little tangible consequence to us. However, because of the way quantum computing flips many long held assumptions on their heads the implications are enormous and far reaching. A close to home example would be the successful demonstration of Shor’s algorithm by Stanford and IBM in 2001. This demonstration showed that a quantum computer can be used to find prime factors of numbers [6], which would render some widely used forms of cryptography like RSA (the kind currently used on the bitcoin blockchain for example) obsolete (don’t panic, quantum safe algorithms such as QKD exist and are a topics of ongoing research)[7]. John Donovan and AT&T seem specifically interested (understandably) in the idea of quantum networks. This concept uses the aforementioned entanglement to change a qubit in one location and induce a change on a distant, entangled qubit, to “move quantum states around in the absence of any communication”[8] .

Though incredibly exciting, there are certainly daunting hurdles.  Current attempts to implement these theories are incredibly complex and to date there are very important open questions. For example, “some quantum physicists aren’t convinced that quantum measurement exists”[3], a fundamental operation of quantum theory as we know it. Despite this, it seems safe to say that  quantum computing shows real promise for quadratic speed up some algorithms, the ability to accurately and effectively simulate and model natural systems and accomplish tasks that are effectively impossible using conventional computers (even teleportation[9]). While the implications (and even some core concepts) of the technology are still not fully understood and hotly debated they are potentially game changing for a number of industries.

 

Disclaimer: I am not well versed in this topic, and so tried to make all claims directly from the sources listed. I chose this topic because I am interested not because I have any related expertise so it should be met with a healthy amount of skepticism.

 

Personal aside: as someone who currently makes a living with zeros and ones I am very interested in this topic, so any insights or useful resources in the comments would be greatly appreciated. Also, if anyone has any experience with related topics being taught/explored here at Stanford I would love to hear about them.

 

[1]http://michaelnielsen.org/blog/quantum-computing-for-everyone/

 

[2]http://www.wired.co.uk/article/quantum-computing-explained

 

[3]https://arstechnica.com/science/2010/01/a-tale-of-two-qubits-how-quantum-computers-work/

 

[4]http://computer.howstuffworks.com/quantum-computer1.htm

 

[5]https://www.research.ibm.com/ibm-q/learn/what-is-quantum-computing/

 

[6]http://english.cas.cn/resources/archive/news_archive/nu2007/201502/t20150215_138749.shtml

 

[7]http://www.idquantique.com/quantum-safe-cryptography/

 

[8]http://math.mit.edu/~ramis/documents/QuantumNetworks_Oxford_Feb2014.pdf

 

[9]https://futurism.com/teleportation-could-possible-using-quantum-physics/

 

Users who have LIKED this post:

•