# Experimental Demonstration of a Robust and Scalable Flux Qubit

A novel rf-SQUID flux qubit that is robust against fabrication variations in Josephson junction critical currents and device inductance has been implemented. Measurements of the persistent current and of the tunneling energy between the two lowest lying states, both in the coherent and incoherent regime, are presented. These experimental results are shown to be in agreement with predictions of a quantum mechanical Hamiltonian whose parameters were independently calibrated, thus justifying the identification of this device as a flux qubit. In addition, measurements of the flux and critical current noise spectral densities are presented that indicate that these devices with Nb wiring are comparable to the best Al wiring rf-SQUIDs reported in the literature thusfar, with a 1/f flux noise spectral density at 1Hz of $1.3^{+0.5}_{-0.7} \; \mu\Phi_0 / \sqrt{Hz}$. An explicit formula for converting the observed flux noise spectral density into a free induction decay time for a flux qubit biased to its optimal point and operated in the energy eigenbasis is presented.

[Soon to be arxiv:0909.4321]

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I'm the chief technology officer of D-Wave and 2010 NAGA Brazilian jiu-jitsu light heavyweight world champion.

## 9 thoughts on “Experimental Demonstration of a Robust and Scalable Flux Qubit”

1. If the singularity happens, it would be cool to be the first one to know.

Not sure what this has to do with flux qubits though.

2. Is the 128 qubit system being sold as a service or product yet ?
Is that happening by the end of 2009 ?
any firm schedule on any bigger systems ?
any change in plans based on any of the recent quantum computer related announcements – more promise scaling trapped ion, photon machine gun qubit clusters, Andrew Houck transmon work, exciton switches etc…

3. Hi Brian, we are talking with some folks about hosting 128 qubit systems so the answer to #1 is “yes”. We are hoping that we can close development partnerships by the end of 2009 (including but not limited to installing systems at a partner’s facility, although the actual installation would finish in late 2010). #2 is “I hope so but there is certainly no guarantee”. For #3 we are focusing for the time being on the 128 qubit chips so “no”. For #4 no change in plans. We do keep up to date with most recent developments and they often give interesting and useful insights. However our objective is the same as it’s been since c.2004, which is to enable adiabatic quantum optimization algorithms for solving Ising model type problems using arrays of niobium rf-squid flux qubits.

4. Hi Geordie,

I have one request: May you please, please, put together a video tutorial and maybe a slide show that goes hand in hand with your technical papers.

If you do that, it will help to clear ambiguities (Quantum Computing stuff is highly ambiguous, and is open to multiple interpretations). This have the benefit of cutting the time you spend clarifying yourself, and it will help people to clearly follow what you are doing.

Otherwise you’re doing a great job in keeping us updated (I’m sure ‘Shtetl-Optimized’ shares the same sentiments as well )

Another final request: An example of how to use the BQP Chimera Algorithm to price path dependent options (binomial options pricing) would be appreciated.

Sincere Regards,

– Craig

5. Hi Craig, that’s a great idea. Let me think about how to do this.

Re. options pricing, I think there is a way to do this, I will discuss with the guys here. If I remember correctly the system is used in a different mode for this… instead of spending a huge amount of time equilibrating a monte carlo simulation prior to drawing samples from some distribution, you use the hardware to quickly perform the equilibration to some (real physical) temperature, then you draw samples from it by repeatedly measuring the system’s state. I think we wrote this up a while back let me check.

6. Also Craig re your runs on the web services, send me an email at rose @ dwavesys.com and I’ll help you reset your parameters so that the jobs run smoothly.

• D-WAVE DEMO CUBIT COMPUTER IS STARTING TO LOOK LIKE A MINIATURE HADRON COLLIDE R,WOULD BE RATHER STRANGE IF THE COMPUTER COULD FIGURE OUT WHAT IT WOULD BE IN THE FUTURE BEFORE THE STRANGE-LET PARTICLE WAS MADE AT CERN
LIKE LOOKING IN TO THE TIME PORTAL. THE HUBBLE TELESCOPE LOOKS INTO THE PAST THIS MEANS WE CAN SEE WHATS TO HAPPEN BEFORE IT HAPPENS TOO LATE! TO SAVE HUMANS FROM DOOMSDAY.P.S. THE CERN LHC NEEDS MAX TERA FLOPS TO CRUNCH THE DATA!